InteractiveFly: GeneBrief

Sox100B: Biological Overview | References

Robust production of terminally differentiated cells from self-renewing resident stem cells is essential to maintain proper tissue architecture and physiological functions, especially in high-turnover tissues. However, the transcriptional networks that precisely regulate cell transition and differentiation are poorly understood in most tissues. This study identified Sox100B, a Drosophila Sox E family transcription factor, as a critical regulator of adult intestinal stem cell differentiation. Sox100B is expressed in stem and progenitor cells and required for differentiation of enteroblast progenitors into absorptive enterocytes. Mechanistically, Sox100B regulates the expression of another critical stem cell differentiation factor, Sox21a. Supporting a direct control of Sox21a by Sox100B, a Sox21a intronic enhancer was identified that is active in all intestinal progenitors and directly regulated by Sox100B. Taken together, these results demonstrate that the activity and regulation of two Sox transcription factors are essential to coordinate stem cell differentiation and proliferation and maintain intestinal tissue homeostasis (Meng, 2020).

The proper maintenance of tissue homeostasis is essential for their normal architecture and physiological functions, especially in high-turnover tissues, such as intestinal epithelium. In most tissues, this is achieved by their resident stem cells, which are capable of self-renewing and differentiating into a variety of cell types within tissues. To answer the fundamental question of how tissue homeostasis is properly maintained, it is critical to identify the genetic networks that control stem cell proliferation and differentiation. Although proliferation has been extensively studied over the decades, mechanisms by which progressive and robust differentiation is achieved in vivo remain less understood in many lineages (Meng, 2020).

The adult Drosophila intestinal epithelium provides a genetically tractable experimental system to examine molecular mechanisms regulating stem cell activities. The adult midgut epithelium is actively maintained by multipotent intestinal stem cells (ISCs), which self-renew to maintain a stable stem cell population and give rise to post-mitotic progenitors committed to one of two distinct cell lineages: diploid secretary enteroendocrine cells (EEs) and polyploid absorptive enterocytes (ECs). In the EC lineage, ISCs turn on the Notch signaling in the daughter cells termed enteroblasts (EBs) that are committed to differentiation into the absorptive fate. EBs then go through several rounds of endo-replication and finally differentiate into Pdm1-positive ECs. To maintain the secretory lineage, ISCs give rise to Prospero-positive pre-EE daughter cells. A number of signaling pathways and transcription factors have been implicated in regulating ISC differentiation, including Delta/Notch, JAK/STAT92E, escargot, Sox21a. However, understanding of the transcriptional network involved in the control of EB differentiation remains incomplete (Meng, 2020).

Sox (Sry-related HMG Box) family transcription factors are important regulators of cell fate specification and cell differentiation during development and in multiple adult stem cell populations. Sox21a, a Drosophila Sox B gene, is specifically expressed in ISCs and EBs and plays important roles in regulating ISC proliferation and EB differentiation into EC, both at homeostasis and under stress conditions (Chen, 2016, Meng, 2015, Zhai, 2015, Zhai, 2017). However, how ISC- and EB-specific Sox21a expression pattern is established remains unknown. This study investigated the expression and function of another Sox family transcription factor, the Sox E factor Sox100B, and found that it is required for ISC differentiation into the EC lineage. Sox100B is required for both Sox21a protein expression and the activity of a transcriptional enhancer located in the first intron of the Sox21a gene. Identification of Sox100B binding sites in this intronic enhancer strongly supports the notion that Sox21a is a direct Sox100B target gene. These results identify an essential player in the transcriptional network that regulates the complex process of stem cell differentiation in the adult Drosophila intestine (Meng, 2020).

This work shows that the Sox E family transcription factor Sox100B is expressed in ISCs and EBs in the adult Drosophila intestine, consistent with a recent report using a GFP-tagged genomic BAC construct for Sox100B (Doupe, 2018). Recently, another Sox family transcription factor Sox21a has already been shown to be expressed specifically in ISCs and EBs (Chen, 2016, Meng, 2015, Zhai, 2015). These two Sox transcription factors do not simply share an overlapping expression pattern, as demonstrated by this work, but Sox100B is required for proper Sox21a expression in both cell types. These data altogether have led to a proposal of a transcriptional cascade in which Sox21a is a Sox100B target gene. The overlapping expression pattern is not surprising, given the fact that Sox factors are commonly co-expressed in several tissues. For example, Drosophila B Group Sox factors SoxNeuro and Dichaete are co-expressed in part of the neuroectoderm during early development of the CNS. However, this study presents evidence showing a direct transcriptional regulation between different Sox factors in the somatic stem cell lineage in Drosophila (Meng, 2020).

Previous studies have shown that transcription factors, such as Stat92E and AP-1 factor Fos are involved in regulating Sox21a expression at basal and stress conditions (Chen, 2016, Meng, 2015, Zhai, 2015). At basal condition, Stat92E has been implicated in regulating Sox21a expression, and the second intron of Sox21a alone is sufficient to drive gene expression in ISCs and EBs (Zhai, 2015); however, whether this intronic enhancer is directly regulated by Stat92E has not been addressed. This study has identified that the first intron of Sox21a is also sufficient to direct endogenous Sox21a expression pattern. Interestingly, this intronic enhancer is not dependent on Stat92E, suggesting that parallel signal inputs from both Sox21a introns act together to robustly control the ISC/EB-specific Sox21a expression pattern. In support of this model, this study found that the first intronic enhancer is specifically responsive to Sox100B. This model is consistent with the observation that Sox21a expression is strongly reduced but not absent in Sox100B mutant clones, suggesting that parallel inputs mediated by the second intron via other factors, such as Stat92E contribute to Sox21a expression even in the absence of Sox100B. This model also partially accounts for the notion that depleting Sox100B does not inhibit ISC proliferation while depleting Sox21a strongly inhibits ISC proliferation (Meng, 2015), and it is likely that residual Sox21a expression in Sox100B loss-of-function conditions allows ISC proliferation. In response to stress, Sox21a expression is strongly induced which involves multiple stress-sensing signaling pathways and factors, such as JNK, EGFR, AP-1 factor Fos, and Stat92E (Meng, 2015, Zhai, 2015, Zhai, 2017). This study has shown that Sox100B is required for stress-, JNK-, and RasV12-induced Sox21a expression but that Sox100B overexpression in ISCs and EBs is not sufficient to induce Sox21a expression. The current data suggest a model where Sox100B provides cell-type specificity and allows Sox21a expression in intestinal progenitors, ISCs and EBs, while other pathways control Sox21a induction during the differentiation process or in response to stresses. This raises an interesting question of whether Sox100B directly interacts with stress-sensing and differentiation pathways to ensure that Sox21a expression is stress inducible and gradually increases during differentiation. As an example of such a mechanism, mammalian Sox9 has been shown to physically interact with AP-1 factors to co-activate target gene expression in developing chondrocytes. It is anticipated that the identification of Sox100B-interacting cofactors will provide a better view regarding the mechanism(s) by which Sox100B cooperates with stress-sensing signaling and other differentiation pathways to precisely adapt stem cell activities to tissue demands (Meng, 2020).

The last decade has witnessed significant advances in understanding the mechanisms by which ISC activities are regulated in response to infection, tissue injury, and during aging, with a strong focus on ISC proliferation. In contrast, a well-defined progressive differentiation process is still inadequately understood. Sox100B has been recently implicated in regulating acute gut regeneration in response to pathogenic bacteria Pseudomonas entomophila (Lan, 2018); however, the exact role of Sox100B in this process has not been characterized. This study found that Sox100B is functionally required for robust stem cell differentiation, as a strong reduction in the EC lineage and a reduction to a lesser extent in the EE lineage were observed in the Sox100B mutant clones. This study further showed that the expression of a critical differentiation regulator Sox21a is reduced in Sox100B mutants, establishing a transcriptional cascade during the ISC differentiation process. However, in preliminary experiments, Sox21a overexpression alone is not sufficient to rescue the differentiation defects of the Sox100B mutants, suggesting that other Sox100B targets, in addition to Sox21a, are required for proper differentiation. Further identification of Sox100B transcriptional target genes is needed to fully decipher the role of Sox100B during the differentiation process (Meng, 2020).

Interestingly, Sox9, the mammalian counterpart of Drosophila Sox100B, is expressed in ISCs and differentiated Paneth cells at the bottom of the crypts. In Sox9 knockout intestine, Paneth cells are found missing and crypt hyperplasia is widely observed (Bastide, 2007, Mori-Akiyama, 2007). This study also observed a mild but significant increase of ISC proliferation in Sox100B loss-of-function conditions, which could be due to disruption of normal differentiation process, since it has been well documented that blocking differentiation process by genetically manipulating Notch and Sox21a causes strong pro-mitotic feedback regulation on ISC proliferation (Chen, 2016, Patel, 2015, Zhai, 2015). In addition to Sox9, several other Sox family factors are expressed in the mammalian intestine, and their expression pattern and function remain elusive. The transcriptional regulatory pattern between different Sox factors in the intestine could be conserved from flies to mammals, and such possibility needs to be further examined (Meng, 2020).

The Drosophila ortholog of mammalian transcription factor Sox9 regulates intestinal homeostasis and regeneration at an appropriate level

Balanced stem cell self-renewal and differentiation is essential for maintaining tissue homeostasis, but the underlying mechanisms are poorly understood. This study identified the transcription factor SRY-related HMG-box (Sox) 100B, which is orthologous to mammalian Sox8/9/10, as a common target and central mediator of the EGFR/Ras and JAK/STAT signaling pathways that coordinates intestinal stem cell (ISC) proliferation and differentiation during both normal epithelial homeostasis and stress-induced intestinal repair in Drosophila. The two stress-responsive pathways directly regulate Sox100B transcription via two separate enhancers. Interestingly, an appropriate level of Sox100B is critical for its function, as its depletion inhibits ISC proliferation via cell cycle arrest, while its overexpression also inhibits ISC proliferation by directly suppressing EGFR expression and additionally promotes ISC differentiation by activating a differentiation-promoting regulatory circuitry composed of Sox100B, Sox21a, and Pdm1. Thus, this study reveals a Sox family transcription factor that functions as a stress-responsive signaling nexus that ultimately controls tissue homeostasis and regeneration (Jin, 2020).

Homeostatic renewal of many adult tissues requires balanced stem cell proliferation and differentiation, a process that is commonly compromised in cancer and in tissue degenerative diseases. The intestinal epithelium in adult Drosophila midgut provides a genetically tractable system for understanding the underlying mechanisms of tissue homeostasis and regeneration driven by resident stem cells. The intestinal stem cells (ISCs) of the Drosophila midgut normally divide to renew themselves and give rise to two different types of progenitor cells that respectively differentiate into enterocyte cells (ECs) and enteroendocrine cells (EEs). Normally, ISCs divide occasionally and thereby maintain the ongoing renewal of the epithelium, a slow process that takes approximately 2-4 weeks. However, upon damage or infection, ISCs are able to rapidly divide to facilitate accelerated epithelial repair in as fast as two days (Jin, 2020).

Extensive studies have implicated the JAK/STAT and the EGFR/Ras/mitogen-activated protein kinase (MAPK) as the two major signaling pathways that regulate ISC proliferation and differentiation during both normal epithelial homeostasis and stress-induced intestinal repair. The EGFR signaling is considered to play a predominant role in the regulation of ISC proliferation because it is required for the JAK/STAT signaling activation-induced ISC proliferation, whereas the JAK/STAT signaling is not essential for EGFR/Ras signaling activation-induced ISC proliferation. The EGFR signaling is also important for remodeling of the differentiated cells, including the exclusion of damaged/aged ECs and incorporation of new cells. The JAK/STAT pathway is also essential for ISC differentiation. ISCs with compromised JAK/STAT activity generate progenitor cells that are incapable of further differentiation. Despite the importance of the two signaling pathways in controlling intestinal homeostasis, their downstream targets-which integrate pathway activities to coordinate ISC proliferation and differentiation-remain elusive (Jin, 2020).

Sox (SRY-related HMG-box) family transcription factors (TFs) are known to have diverse roles in cell-fate specification and differentiation in multicellular organisms. In mouse-small intestine, Sox9, a SoxE subfamily member, is expressed in ISCs to regulate ISC proliferation and differentiation, but whether it acts as an oncogene or a tumor suppressor is still in debate. In Drosophila midgut, Sox21a, a SoxB2 subfamily member, is specifically expressed in ISCs and transient progenitor cells, and is essential for progenitor cell differentiation into mature cells (Chen, 2016, Zhai, 2015, Zhai, 2017). This study identified Sox100B, the Drosophila ortholog of Sox9, as a common downstream gene target for both the JAK/STAT and the EGFR signaling in regulating ISC proliferation and differentiation. This study also revealed that an appropriate level of Sox100B is critical for its function in regulating ISC proliferation, in that it may allow it to serve as an important mediator for a balanced process of ISC proliferation and differentiation, thereby maintaining intestinal homeostasis (Jin, 2020).

Although it has been well established that in the Drosophila midgut, the stress-responsive JAK/STAT signaling and EGFR/Ras/MAPK signaling are the two major signaling pathways that regulate ISC proliferation and differentiation, the downstream signaling targets that coordinate ISC proliferation and differentiation for intestinal regeneration are still yet to be identified. Sox100B identified in this study may represent such a key target. First, the expression of Sox100B is regulated by both JAK/STAT- and EGFR-signaling pathways. Normally Sox100B is expressed specifically in ISCs and EBs, where JAK/STAT- and EGFR/Ras/MAPK-pathway activities are high, and its expression is highly dependent on the activity of JAK/STAT- and EGFR/Ras/MAPK-signaling activities. Second, similar to the functions of JAK/STAT and EGFR signaling, Sox100B is critically required for both ISC proliferation and differentiation. The sustained EGFR/Ras/MAPK activity in EBs is important for the initiation of DNA endoreplication during the process of EC differentiation, and the sustained JAK/STAT signaling activity in EBs is essential for terminal differentiation toward both EC and EE lineage. Depletion of Sox100B causes ISC quiescence, similar to that caused by the disruption of EGFR signaling, as well as arrest of EB differentiation, similar to that caused by the disruption of JAK/STAT signaling. Third, an appropriate level of Sox100B expression appears to be critical for intestinal homeostasis. This effect by the expression level, as well as its responsiveness to JAK/STAT, EGFR, and potentially other stress-induced signaling activities (not shown), such as Wnt and Hippo signaling, may position Sox100B as a central mediator that coordinates ISC proliferation and differentiation during intestinal homeostasis and regeneration in Drosophila (Jin, 2020).

Sox100B is a Sox family group-E transcription factor, homolog of mammalian Sox8/9/10. In mouse small intestine, Sox9 is expressed in stem cells and progenitor cells at the base of crypts, and loss of Sox9 in the intestinal epithelium causes ISC hyperplasia and failure of Paneth cell differentiation (Bastide, 2007, Mori-Akiyama, 2007). Interestingly, in the stem cell zone, Sox9 is expressed at low levels in ISCs and high levels in the quiescent or reserved stem cells that are also considered as the secretory progenitors. A possible explanation for these observations is that a low level of Sox9 sustains actively dividing ISCs, while an increase of SOX9 converts these proliferating ISCs into quiescent ISCs that will eventually differentiate into Paneth cells. Similarly, Sox9 is also implicated in regulating colorectal cancer cells, but there are conflicting data regarding whether Sox9 functions as an oncogene or a tumor suppressor. These seemingly contradictory results can be reconciled with a proposed model that Sox9 functions at an appropriate level, with a critical dose of Sox9 that exhibits proliferation-promoting activity, while increasing or decreasing this dose both result in proliferation-inhibitory activity. It is worthy to note that the differentiation-promoting function of Sox9 could potentially further complicate the interpretation of the mutant phenotype. It has been shown in Drosophila gut that defects in differentiation can induce a stressed microenvironment that promotes cell proliferation and propels tumor development (Jin, 2020).

The results of this study suggest many aspects of functional conservation of this Sox E subfamily gene in ISCs from Drosophila to mammals. Sox100B regulates both ISC proliferation and differentiation in the Drosophila intestine, and in terms of regulating ISC proliferation, Sox100B also requires an appropriate expression level. This study has demonstrated that this modulation of Sox100B expression is largely due to a negative feedback mechanism, in which increased Sox100B caused by elevated EGFR/Ras/MAPK signaling in turn suppresses the expression of EGFR, thereby leading to damped EGFR-signaling activity. Of note, contradictory data were recently reported on the roles of Sox100B and Sox21a in regulating ISC proliferation: both a proliferation-promoting role (Meng, 2015) and a tumor-suppressive role (Chen, 2016, Zhai, 2015) for Sox21a in ISCs have been reported; as for the role of Sox100B, Lan (2018) showed in an RNAi genetic screen that Sox100B is required for P.e.-induced ISC proliferation, whereas Doupé (2018) showed that depletion of Sox100B by RNAi causes increased ISC proliferation. Consideration of the effects caused by different levels of Sox100B expression that was observed in the present study may help resolve understanding of apparently disparate functions for these genes as central coordinators of both ISC proliferation and differentiation. It is proposed that, normally, a low level of Sox protein expression sustains ISC proliferation. A transient increase of Sox protein may not only promote cell cycle exit but also activate programs for terminal differentiation, thereby leading to a coordinated ISC proliferation and differentiation and, consequently, a coherent process of epithelial renewal (Jin, 2020).

This study demonstrates that Sox100B directly regulates Sox21a to promote differentiation. One important downstream target of Sox100B and Sox21a appears to be Pdm1, a known EC-fate-promoting factor. Interestingly, overexpression of Pdm1 in progenitor cells rapidly shuts down both Sox100B and Sox21a expression, indicating a negative feedback mechanism. Therefore, the induced Sox100B-Sox21a-Pdm1 axis in the differentiating ECs not only promotes cell differentiation, but also acts in a feedback mechanism to turn down EGFR and JAK/STAT signaling activities, thereby allowing ECs to terminally differentiate. This differentiation-promoting axis might also have a role in turning down ISC-specific programs, which are independently regulated by EGFR or JAK/STAT signaling pathways. For example, downregulation of the stem-cell-factor Esg is required for EB differentiation, and ectopic expression of Pdm1 is able to antagonize Esg expression in progenitor cells. These kinds of feedback regulation could be a common strategy used for initiation and finalization of a cell-differentiation program (Jin, 2020).

In summary, this study identified the transcription factor Sox100B as a major effector downstream of JAK/STAT and EGFR pathways that acts at an appropriate level to coordinate ISC proliferation and differentiation during both normal intestinal homeostasis and during damage- and infection-induced intestinal regeneration in Drosophila. With the 'just-right' effect endowed by a feedback mechanism, Sox100B behaves as a homeostatic sensor in the intestinal epithelium that coordinates stem cell proliferation with stem cell differentiation under various environmental conditions. It is proposed that this expressional and functional modulation associated with Sox family transcription factors may be a general mechanism for maintaining tissue homeostasis and regeneration in many organs, including those in mammals, and that deregulation of this mechanism may lead to tissue degeneration or cancer development (Jin, 2020).

Estrogen related receptor is required for the testicular development and for the normal sperm axoneme/mitochondrial derivatives in Drosophila males

Estrogen related receptors (ERRs), categorized as orphan nuclear receptors, are critical for energy homeostasis and somatic development. However, significance of ERRs in the development of reproductive organs/organelles/cells remain poorly understood, albeit their homology to estrogen receptors. In this context, this study shows that knockdown of ERR in the testes leads to improperly developed testes with mis-regulation of genes (aly, mia, bruce, bam, bgcn, fzo and eya) involved in spermatogenesis, resulting in reduced male fertility. The observed testicular deformity is consistent with the down-regulation of SOX-E group of gene (SOX100B) in Drosophila. Dispersion/disintegration of fusomes (microtubule based structures associated with endoplasmic reticulum derived vesicle, interconnecting spermatocytes) was demonstrated in ERR knockdown testes. A few ERR knockdown testes go through spermatogenesis but have significantly fewer sperm. Moreover, flagella of these sperm are defective with abnormal axoneme and severely reduced mitochondrial derivatives, suggesting a possible role for ERR in mitochondrial biogenesis, analogous to mammalian ERRalpha. Interestingly, similar knockdown of remaining seventeen nuclear receptors did not yield a detectable reproductive or developmental defect in Drosophila. These findings add newer dimensions to the functions envisaged for ERR and provide the foundation for deciphering the relevance of orphan nuclear receptors in ciliopathies and testicular dysgenesis (Misra, 2017).

Sox100B, a Drosophila group E Sox-domain gene, is required for somatic testis differentiation

Sex determination mechanisms are thought to evolve rapidly and show little conservation among different animal species. For example, the critical gene on the Y chromosome, SRY, that determines sex in most mammals, is not found in other animals. However, a related Sox domain transcription factor, SOX9, is also required for testis development in mammals and exhibits male-specific gonad expression in other vertebrate species. Previously, it was found that the Drosophila orthologue of SOX9, Sox100B, is expressed male-specifically during gonad development. This study now investigates the function of Sox100B and finds, strikingly, that Sox100B is essential for testis development in Drosophila. In Sox100B mutants, the adult testis is severely reduced and fails to interact with other parts of the reproductive tract, which are themselves unaffected. While a testis initially forms in Sox100B mutants, it fails to undergo proper morphogenesis during pupal stages, likely due to defects in the pigment cells. In contrast, no substantive defects are observed in ovary development in Sox100B mutant females. Thus, as is observed in mammals, a Sox9 homolog is essential for sex-specific gonad development in Drosophila, suggesting that the molecular mechanisms regulating sexually dimorphic gonad development may be more conserved than previously suspected (Nanda, 2009).

Sex-specific apoptosis, dependent on doublesex, regulates sexual dimorphism in the Drosophila embryonic gonad

Sexually dimorphic development of the gonad is essential for germ cell development and sexual reproduction. The Drosophila embryonic gonad is already sexually dimorphic at the time of initial gonad formation. Male-specific somatic gonadal precursors (msSGPs) contribute only to the testis and express a Drosophila homolog of Sox9 (Sox100B: Loh, 2000), a gene essential for testis formation in humans. The msSGPs are specified in both males and females, but are recruited into only the developing testis. In females, these cells are eliminated via programmed cell death dependent on the sex determination regulatory gene doublesex. This work furthers the hypotheses that a conserved pathway controls gonad sexual dimorphism in diverse species and that sex-specific cell recruitment and programmed cell death are common mechanisms for creating sexual dimorphism (DeFalco, 2003).

To investigate when sexual dimorphism is first manifested in the somatic gonad, expression of SGP markers were examined in embryos whose sex could be unambiguously identified, at a developmental stage (stage 15) soon after gonad coalescence has occurred. Analysis of Eya expression reveals anti-Eya immunoreactivity throughout the female somatic gonad, though Eya expression is somewhat stronger in the posterior. In males, anti-Eya immunoreactivity is also found throughout the somatic gonad. However, the expression at the posterior of the gonad is much more intense than in females, as there appears to be a cluster of Eya-expressing cells at the posterior of the male gonad that is not present in females. In blind experiments, the sex of an embryo could be accurately identified by the Eya expression pattern in the gonad. Thus, sexual dimorphism is already apparent in the somatic gonad soon after initial gonad formation. A sex-specific expression pattern is also observed with Wnt-2 at this stage. As is observed with Eya, Wnt-2 is expressed in the SGPs of the female gonad, but its expression is greatly increased at the posterior of the male gonad. The SGP marker bluetail (see Galloni, 1993) exhibits a similar sex-specific pattern as Eya; however, the SGP marker 68-77 is expressed equally in both sexes (see below). Thus, the somatic gonad is sexually dimorphic by stage 15, but only a subset of SGP markers reveals this sexual dimorphism (DeFalco, 2003).

During Drosophila embryogenesis, Sox100B is expressed in a number of cell types, including the gonad (Loh, 2000). Since Sox100B is closely related to Sox9 (an important sex determination factor in humans and mice), whether Sox100B expression is sexually dimorphic in Drosophila was tested. Interestingly, it was found that after gonad coalescence (stage 15), Sox100B expression in the gonad is male-specific. Sox100B immunoreactivity is not observed in the coalesced female gonad, whereas it is detected in a posterior cluster of SGPs in the male gonad. While this expression pattern is seen in most wild-type backgrounds (including Canton-S and faf-lacZ), in certain 'wild-type' lines, such as w¹¹¹⁸, a few Sox100B-positive cells are observed in the posterior of the coalesced female gonad (however, this is still clearly distinguishable from the number of Sox100B-positive cells in the male). Unlike Eya and Wnt-2, Sox100B is not expressed in all SGPs, since it is usually absent from female gonads and from the anterior region of the male gonad and does not colocalize with the SGP marker 68-77. Sox100B expression appears restricted to the posterior cluster of SGPs that is observed only in the male gonad. Thus, like Sox9 expression in vertebrates, Sox100B exhibits a male-specific pattern of expression in the Drosophila embryonic gonad, suggesting that it may indeed be an ortholog of Sox9 (DeFalco, 2003).

After having identified sexually dimorphic markers of the embryonic gonad, these markers were used to investigate how sexual dimorphism is established. It was asked whether proper gonad formation is necessary for the establishment of sexual dimorphism by examining Sox100B expression in fear-of-intimacy (foi) mutant embryos. In foi mutants, germ cells migrate and associate normally with the SGPs, but these two cell types fail to coalesce into a round and compact gonad. Despite the failure of gonad coalescence, a cluster of Sox100B-expressing cells was still observed at the posterior of the male gonad, while no Sox100B-expressing cells are observed in the female at this stage. Whether the presence of germ cells is necessary for the establishment of sexual dimorphism in the embryonic gonad was examined. Embryos that lack germ cells due to a hypomorphic mutation in oskar, a gene required for germ cell formation, were examined. Other aspects of embryonic development occur normally in these embryos, including the formation and coalescence of the SGPs. Agametic gonads show identical sexual dimorphism to wild-type embryos. Sox100B is coexpressed with Eya in the cluster of somatic cells in the posterior of the male gonad, but Sox100B expression is not observed in the female gonad. Thus, sexual dimorphism of the embryonic somatic gonad does not require proper gonad morphogenesis or the presence of germ cells (DeFalco, 2003).

The posterior cluster of Eya and Sox100B coexpressing cells could result from sex-specific differences in gene expression within the cells of the gonad. Alternatively, it could reflect a difference in gonad morphology, in which these cells are only present in males and not in females. To distinguish between these possibilities, the morphology of the male and female coalesced (stage 15) gonad was examined, using approaches that do not depend on cell-type-specific SGP markers. First, a CD8-GFP fusion protein was expressed broadly in the mesoderm. The fusion of the extracellular and transmembrane regions of mouse CD8 with GFP allows for visualization of cell and tissue morphology. A cluster of mesodermal cells is consistantly observed attached to the posterior of the male gonad that is not observed in the female. In blind experiments, the sex of the embryo can be predicted based on the presence of this posterior cluster of cells. Male and female gonads were also examined by transmission electron microscopy (TEM). Male and female embryos were first sorted using an X chromosome-linked GFP expression construct and then processed separately for TEM. In this analysis, a cluster of cells that is not present in the female gonad was consistently at the posterior of the male gonad. Both the size and morphology of these cells indicate that they are somatic cells rather than germ cells. Thus, the observed sexual dimorphism reflects a change in gonad morphology, not just a change in gene expression. Since the additional cells at the posterior of the male gonad express at least some markers in common with SGPs (e.g., Eya), these cells are referred to as male-specific SGPs (msSGPs) (DeFalco, 2003).

Since no sex-specific differences were observed in SGP proliferation in the gonad, it seems unlikely that the SGPs are dividing to produce the msSGPs. Therefore, Sox100B was used as a marker for the msSGPs to determine where and when these cells are first specified. At stages prior to gonad coalescence (stages 12 and 13), a cluster of Eya/Sox100B double-immunopositive cells is observed posterior and ventral to the developing clusters of SGPs, which express Eya alone. Interestingly, this cluster of Eya/Sox100B double-positive cells is initially observed in both males and females and appears identical, although Eya expression may be somewhat lower in the female cluster. During stage 13, as the SGPs and germ cells associate closely along PS 10-12, the Eya/Sox100B double-positive cells move toward the gonad in both sexes. In males, these cells join the posterior of the coalescing gonad. In contrast, these cells do not join the gonad in females, and only Eya-positive, Sox100B-negative cells are found in the coalesced gonad. It is concluded that the Eya/Sox100B double-positive cells are the msSGPs and that they form separately from the SGPs. These cells are initially specified in both males and females and move anteriorly to join the gonad in males. In females, these cells do not form part of the gonad, as judged by the above morphological analysis, and are no longer detected using available markers (DeFalco, 2003).

Since the msSGPs develop separately from the SGPs, it was of interest to address where the msSGPs arise and what controls their specification. By marking the anterior of each parasegment using an antibody against Engrailed, it was determined that the msSGPs are specified in PS13. This observation is consistent with these cells arising posterior to the SGPs, which form in PS 10, 11, and 12. Other Sox100B expression is observed in nongonadal tissues. Whether, like the SGPs, the msSGPs are specified in the dorsolateral domain of the mesoderm was also addressed. Mesodermal cell types that form in this region, such as the SGPs and the fat body, require the homeodomain proteins Tinman and Zfh-1 for their specification. However, in embryos double-mutant for tinman and zfh-1, the msSGPs are still specified, even though the SGPs fail to develop. Thus, msSGPs do not arise from the dorsolateral domain, consistent with the fact that the msSGPs are first observed in a position ventral to the SGPs. The msSGPs also differ from the SGPs in terms of their requirements for the homeotic gene abd-A. SGP specification absolutely requires abd-A, while msSGPs are still present in these mutants. Thus, despite the fact that the msSGPs and the SGPs share expression of some molecular markers such as Eya and Wnt-2, their specification is under independent control (DeFalco, 2003).

Since the msSGPs express both Eya and Sox100B, the requirements for each of these genes in msSGP specification was investigated. In eya mutants, Sox100B-positive cells are still observed posterior to the germ cells at early stages, in a position where the msSGPs normally develop. Since the SGPs are not maintained in these mutants, the germ cells disperse and the gonad does not coalesce. Therefore, it is impossible to tell if the msSGPs would join the posterior of the male gonad in eya mutants. However, initial msSGP specification does not require eya. Similarly, in a deletion that removes the Sox100B locus, a large cluster of Eya-positive cells was still observed at the posterior of the male gonad that does not appear in females. Thus, the initial development of the msSGPs does not require Sox100B. Expression of Eya and Sox100B are mutually independent and are likely to be downstream of factors controlling initial msSGP specification (DeFalco, 2003).

Since the msSGPs are initially specified in both males and females, a determination was made of how these cells receive information about their sexual identity that allows them to behave differently in the two sexes. tra plays a key role in the sex determination pathway in Drosophila and is required to promote female differentiation in somatic tissues. tra mutant gonads were examined to test if tra function is required for gonad sexual dimorphism (XX embryos are masculinized by mutations in tra). Sox100B-immunopositive cells are observed in the posterior somatic gonad of both XX and XY tra mutant embryos in a manner comparable to wild-type males. Analysis of the Sox100B expression pattern in the gonad reveals that there are no differences between XX and XY tra mutants, or between either of these genotypes and wild-type males. Conversely, when Transformer is expressed in XY embryos (UAS-tra^F, tubulin-GAL4), Sox100B-immunopositive cells are no longer observe in these gonads, and they now appear similar to wild-type females (DeFalco, 2003).

In most somatic tissues, the principle sex determination factor downstream of tra is dsx. Unlike tra, dsx is required for both the male and female differentiation pathway, since both XX and XY dsx mutant adults show an intersexual phenotype. However, in the somatic gonad, dsx mutant XY embryos are indistinguishable from wild-type males and show no change in Sox100B expression. Thus, unlike in most somatic tissues, this early characteristic of male development does not require dsx. In XX embryos that are mutant for dsx, a completely masculinized phenotype is observed, in which Sox100B expression in the gonad is similar to a wild-type male. When a dominant allele of dsx, dsx^D, is used to express Dsx^M (dsx^D/dsx) in XX embryos, these gonads are no more masculinized than dsx null XX gonads. Therefore, while Dsx^F is required for the proper female phenotype in XX gonads, it appears that the male Sox100B expression pattern is the 'default' state in the absence of dsx function (DeFalco, 2003).

Since the msSGPs join the posterior of the male gonad but are no longer detected in the female, the basis for the sexually dimorphic behavior of these cells was investigated. In the female, these cells could turn off Sox100B and Eya and contribute to some other tissue, or they might be eliminated altogether. To test this latter hypothesis, whether msSGPs are eliminated by sex-specific programmed cell death in the female was addressed. Since programmed cell death occurs in a caspase-dependent manner, the gonad phenotype was examined in embryos in which caspase activity was inhibited by expressing the baculovirus p35 protein in the mesoderm. In these embryos, XX gonads now appear masculinized; Sox100B-positive cells (msSGPs) persist and join the posterior of female gonads, and coexpress Eya, as in wild-type male embryos. There are not as many Sox100B-positive cells in females as in males, suggesting that p35 may not be completely suppressing cell death. The presence of such cells in the female gonad does not appear to drastically affect ovary formation or oogenesis, since embryos develop into fertile adult females (DeFalco, 2003).

To investigate how programmed cell death might be controlled in the msSGPs, the genes of the H99 region (head involution defective [hid], reaper [rpr], and grim), which are regulators of apoptosis in Drosophila, were examined. A small deletion (DfH99) removes all three of these genes and blocks most programmed cell death in the Drosophila embryo. In DfH99 mutants, an equivalent cluster of Sox100B-positive cells is observed in both males and females. Again, these posterior cells are also Eya positive. Furthermore, XX embryos mutant for hid alone also contain Sox100B-positive cells in the posterior of the gonad, although the posterior cluster of cells is slightly smaller than in the male. It is concluded that the msSGPs are normally eliminated from females through sex-specific programmed cell death, controlled by hid and possibly also other genes of the H99 region. However, if cell death is blocked in females, these cells can continue to exhibit the normal male behavior of the msSGPs, including proper marker expression and recruitment into the gonad. Therefore, the decision whether or not to undergo apoptosis is likely the crucial event leading to the sexually dimorphic development of these cells at this stage (DeFalco, 2003).

It is concluded that proper information from the sex determination pathway is required to control the sexually dimorphic behavior of the msSGPs. The female phenotype in the embryonic gonad is dependent on both tra and dsx. Interestingly, it seems that the male phenotype is the default state; in the absence of any tra or dsx function, msSGPs in both XX and XY embryos behave as in wild-type males. This is a different situation than in most other tissues, in which dsx is required in both sexes to promote proper sexual differentiation. In particular, while no role is found for Dsx^M in this process, Dsx^F is positively required either to establish the female fate in the posterior somatic gonad or to repress the male fate. This role for Dsx^F in msSGP development is analogous to its role in the genital disc, in which Dsx^F is required to block recruitment of btl-expressing cells into the disc; in both cases, dsx female function serves to repress incorporation of a male-specific cell type. Since the msSGPs are initially specified in a sex-independent manner, this may account for the fact that the persistence of these cells (the male phenotype) is the default state. It will be of interest in the future to address the role of the msSGPs in testis development, and how genes such as dsx, eya, and Sox100B act in this process (DeFalco, 2003).

Although sex determination schemes vary widely in the animal kingdom, there is evidence that the molecular and cellular pathways used to control sexual dimorphism may be conserved, even between vertebrates and invertebrates. One example is Sox9, which has been implicated as an ancestral sex-determining gene in vertebrates given its male-specific gonad expression in diverse species such as human, mouse, turtle, and chicken. A potential Drosophila ortholog of Sox9, Sox100B, is expressed in a male-specific manner in the embryonic somatic gonad. The manner of Sox100B expression is reminiscent of that in the mouse; Sox9 is initially expressed in both sexes, but is maintained and upregulated in the male gonad. It will be very interesting to compare the role that Sox100B plays in the development of the Drosophila testis to the one played by Sox9 in vertebrates (DeFalco, 2003).

Molecular conservation is also observed amongst the members of the Dsx/Mab-3 Related Transcription Factor (DMRT) family. DMRT family members have been shown to be essential for sex-specific development in Drosophila (Dsx), C. elegans (mab-3), medaka fish (DMY), and mice (DMRT1) and have been implicated in human sex reversal. This study demonstrates that dsx is essential for proper sex-specific development of the msSGPs. Thus, increasing evidence indicates that DMRT family members are also conserved regulators of sexual dimorphism (DeFalco, 2003).

A Drosophila group E Sox gene is dynamically expressed in the embryonic alimentary canal

This study has identified a novel Drosophila Sox-domain gene, Sox100B, related to the vertebrate group E genes Sox9 and Sox10. In vertebrates, group E Sox genes are expressed in the developing gonad, adult kidney and gut as well as other tissues. During embryogenesis in Drosophila, Sox100B is expressed in two rows of large intestinal cells, in midgut basophilic cells, in the Malpighian tubules and at the posterior cap of gonadal mesoderm. These observations indicate that aspects of tissue-specific expression, as well as sequence, are conserved between vertebrate and invertebrate group E Sox proteins (Loh, 2000).

Context-specific role of SOX9 in NF-Y mediated gene regulation in colorectal cancer cells

Roles for SOX9 have been extensively studied in development and particular emphasis has been placed on SOX9 roles in cell lineage determination in a number of discrete tissues. Aberrant expression of SOX9 in many cancers, including colorectal cancer, suggests roles in these diseases as well and recent studies have suggested tissue- and context-specific roles of SOX9. A genome wide approach by chromatin immunoprecipitation sequencing (ChIP-seq) in human colorectal cancer cells identified a number of physiological targets of SOX9, including ubiquitously expressed cell cycle regulatory genes, such as CCNB1 and CCNB2, CDK1, and TOP2A. These novel high affinity-SOX9 binding peaks precisely overlapped with binding sites for histone-fold NF-Y (see Drosophila Nf-YA) transcription factor. Furthermore, the data showed that SOX9 is recruited by NF-Y to these promoters of cell cycle regulatory genes and that SOX9 is critical for the full function of NF-Y in activation of the cell cycle genes. Mutagenesis analysis and in vitro binding assays provided additional evidence to show that SOX9 affinity is through NF-Y and that SOX9 DNA binding domain is not necessary for SOX9 affinity to those target genes. Collectively, these results reveal possibly a context-dependent, non-classical regulatory role for SOX9 (Shi 2015).

The transcription factors SOX9 and SOX5/SOX6 cooperate genome-wide through super-enhancers to drive chondrogenesis

SOX9 is a transcriptional activator required for chondrogenesis, and SOX5 and SOX6 are closely related DNA-binding proteins that critically enhance its function. This study used genome-wide approaches to gain novel insights into the full spectrum of the target genes and modes of action of this chondrogenic trio. Using the RCS cell line as a faithful model for proliferating/early prehypertrophic growth plate chondrocytes, SOX6 and SOX9 were shown to bind thousands of genomic sites, frequently and most efficiently near each other. SOX9 recognizes pairs of inverted SOX motifs, whereas SOX6 favors pairs of tandem SOX motifs. The SOX proteins primarily target enhancers. While binding to a small fraction of typical enhancers, they bind multiple sites on almost all super-enhancers (SEs) present in RCS cells. These SEs are predominantly linked to cartilage-specific genes. The SOX proteins effectively work together to activate these SEs and are required for in vivo expression of their associated genes. These genes encode key regulatory factors, including the SOX trio proteins, and all essential cartilage extracellular matrix components. Chst11, Fgfr3, Runx2 and Runx3 are among many other newly identified SOX trio targets. SOX9 and SOX5/SOX6 thus cooperate genome-wide, primarily through SEs, to implement the growth plate chondrocyte differentiation program (Liu, 2015).

SOX9 regulates multiple genes in chondrocytes, including genes encoding ECM proteins, ECM modification enzymes, receptors, and transporters

The transcription factor SOX9 plays an essential role in determining the fate of several cell types and is a master factor in regulation of chondrocyte development. The aim of this study was to determine which genes in the genome of chondrocytes are either directly or indirectly controlled by SOX9. RNA-Seq was used to identify genes whose expression levels were affected by SOX9 and used SOX9 ChIP-Seq to identify those genes that harbor SOX9-interaction sites. For RNA-Seq, the RNA expression profile of primary Sox9flox/flox mouse chondrocytes infected with Ad-CMV-Cre was compared with that of the same cells infected with a control adenovirus. Analysis of RNA-Seq data indicated that, when the levels of Sox9 mRNA were decreased more than 8-fold by infection with Ad-CMV-Cre, 196 genes showed a decrease in expression of at least 4-fold. These included many cartilage extracellular matrix (ECM) genes and a number of genes for ECM modification enzymes (transferases), membrane receptors, transporters, and others. In ChIP-Seq, 75% of the SOX9-interaction sites had a canonical inverted repeat motif within 100 bp of the top of the peak. SOX9-interaction sites were found in 55% of the genes whose expression was decreased more than 8-fold in SOX9-depleted cells and in somewhat fewer of the genes whose expression was reduced more than 4-fold, suggesting that these are direct targets of SOX9. The combination of RNA-Seq and ChIP-Seq has provided a fuller understanding of the SOX9-controlled genetic program of chondrocytes (Oh, 2014).

Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways

During endochondral bone formation, Sox9 expression starts in mesenchymal progenitors, continues in the round and flat chondrocyte stages at high levels, and ceases just prior to the hypertrophic chondrocyte stage. Sox9 is important in mesenchymal progenitors for their differentiation into chondrocytes, but its functions post-differentiation have not been determined. To investigate Sox9 function in chondrocytes, mouse Sox9 was deleted at two different steps after chondrocyte differentiation. Sox9 inactivation in round chondrocytes resulted in a loss of Col2a1 expression and in apoptosis. Sox9 inactivation in flat chondrocytes caused immediate terminal maturation without hypertrophy and with excessive apoptosis. Inactivation of Sox9 in the last few cell layers resulted in the absence of Col10a1 expression, suggesting that continued expression of Sox9 just prior to hypertrophy is necessary for chondrocyte hypertrophy. SOX9 knockdown also caused apoptosis of human chondrosarcoma SW1353 cells. These phenotypes were associated with reduced Akt phosphorylation. Forced phosphorylation of Akt by Pten inactivation partially restored Col10a1 expression and cell survival in Sox9(floxdel/floxdel) mouse chondrocytes, suggesting that phosphorylated Akt mediates chondrocyte survival and hypertrophy induced by Sox9. When the molecular mechanism of Sox9-induced Akt phosphorylation was examined, expression of the PI3K subunit Pik3ca (p110alpha) was found to be decreased in Sox9(floxdel/floxdel) mouse chondrocytes. Sox9 binds to the promoter and enhances the transcriptional activities of Pik3ca. Thus, continued expression of Sox9 in differentiated chondrocytes is essential for subsequent hypertrophy and sustains chondrocyte-specific survival mechanisms by binding to the Pik3ca promoter, inducing Akt phosphorylation (Ikegami, 2011).

Replacement of mouse Sox10 by the Drosophila ortholog Sox100B provides evidence for co-option of SoxE proteins into vertebrate-specific gene-regulatory networks through altered expression

Neural crest cells and oligodendrocytes as the myelinating glia of the central nervous system exist only in vertebrates. Their development is regulated by complex regulatory networks, of which the SoxE-type high-mobility-group domain transcription factors Sox8, Sox9 and Sox10 are essential components. This study analyzed by in ovo electroporation in chicken and by gene replacement in the mouse whether the Drosophila ortholog Sox100B can functionally substitute for vertebrate SoxE proteins. Sox100B overexpression in the chicken neural tube led to the induction of neural crest cells as previously observed for vertebrate SoxE proteins. Furthermore, many aspects of neural crest and oligodendrocyte development were surprisingly normal in mice in which the Sox10 coding information was replaced by Sox100B arguing that Sox100B integrates well into the gene-regulatory networks that drive these processes. These results therefore provide strong evidence for a model in which SoxE proteins were co-opted to these gene-regulatory networks mainly through the acquisition of novel expression patterns. However, later developmental defects in several neural crest derived lineages in mice homozygous for the Sox100B replacement allele indicate that some degree of functional specialization and adaptation of SoxE protein properties have taken place in addition to the co-option event (Cossais, 2010).

Sox9 regulates cell proliferation and is required for Paneth cell differentiation in the intestinal epithelium

The HMG-box transcription factor Sox9 is expressed in the intestinal epithelium, specifically, in stem/progenitor cells and in Paneth cells. Sox9 expression requires an active beta-catenin-Tcf complex, the transcriptional effector of the Wnt pathway. This pathway is critical for numerous aspects of the intestinal epithelium physiopathology, but processes that specify the cell response to such multipotential signals still remain to be identified. This study inactivated the Sox9 gene in the intestinal epithelium to analyze its physiological function. Sox9 inactivation affected differentiation throughout the intestinal epithelium, with a disappearance of Paneth cells and a decrease of the goblet cell lineage. Additionally, the morphology of the colon epithelium was severely altered. General hyperplasia and local crypt dysplasia were detected in the intestine, and Wnt pathway target genes were up-regulated. These results highlight the central position of Sox9 as both a transcriptional target and a regulator of the Wnt pathway in the regulation of intestinal epithelium homeostasis (Bastide, 2007).

SOX9 is required for the differentiation of paneth cells in the intestinal epithelium

The transcription factor SOX9 has been shown previously to have an essential role in the differentiation of a small number of discrete cell lineages. In the intestine, Sox9 is expressed in the epithelial cells of the crypts and is a target of Wnt signaling. To examine the function of SOX9 in the intestine, the Sox9 gene was inactivated in intestinal epithelial cells by generating mice that harbored a conditional Sox9 gene and a Villin-Cre transgene. In the absence of SOX9, Paneth cells were not formed, but the differentiation of other intestinal epithelial cell types was unaffected. The lack of SOX9 also lead to crypt enlargement, to a marked increase in cell proliferation throughout the crypts, and to replacement of the Paneth cells by proliferating epithelial cells. It is concluded that SOX9 is required for the differentiation of Paneth cells. The results elucidate an essential step in the differentiation of gut epithelium (Mori-Akiyama, 2007).

Homozygous inactivation of Sox9 causes complete XY sex reversal in mice

In the presence of the Y-chromosomal gene Sry, the bipotential mouse gonads develop as testes rather than as ovaries. The autosomal gene Sox9, a likely and possibly direct Sry target, can induce testis development in the absence of Sry. Sox9 is thus sufficient but not necessarily essential for testis induction. Mutational inactivation of one allele of SOX9/Sox9 causes sex reversal in humans but not in mice. Because Sox9(-/-) embryos die around Embryonic Day 11.5 (E11.5) at the onset of testicular morphogenesis, differentiation of the mutant XY gonad can be analyzed only ex vivo in organ culture. This study has therefore conditionally inactivated both Sox9 alleles in the gonadal anlagen using the CRE/loxP recombination system, whereby CRE recombinase is under control of the cytokeratin 19 promoter. Analysis of resulting Sox9(-/-) XY gonads up to E15.5 reveals immediate, complete sex reversal, as shown by expression of the early ovary-specific markers Wnt4 and Foxl2 and by lack of testis cord and Leydig cell formation. Sry expression in mutant XY gonads indicates that downregulation of Wnt4 and Foxl2 is dependent on Sox9 rather than on Sry. These results provide in vivo proof that, in contrast to the situation in humans, complete XY sex reversal in mice requires inactivation of both Sox9 alleles and that Sox9 is essential for testogenesis in mice (Barrionuevo, 2006).

Search PubMed for articles about Drosophila Sox100B

Barrionuevo, F., Bagheri-Fam, S., Klattig, J., Kist, R., Taketo, M. M., Englert, C. and Scherer, G. (2006). Homozygous inactivation of Sox9 causes complete XY sex reversal in mice. Biol Reprod 74(1): 195-201. PubMed ID: 16207837

Bastide, P., Darido, C., Pannequin, J., Kist, R., Robine, S., Marty-Double, C., Bibeau, F., Scherer, G., Joubert, D., Hollande, F., Blache, P. and Jay, P. (2007). Sox9 regulates cell proliferation and is required for Paneth cell differentiation in the intestinal epithelium. J Cell Biol 178(4): 635-648. PubMed ID: 17698607

Chen, J., Xu, N., Huang, H., Cai, T. and Xi, R. (2016). A feedback amplification loop between stem cells and their progeny promotes tissue regeneration and tumorigenesis. Elife 5. PubMed ID: 27187149

Cossais, F., Sock, E., Hornig, J., Schreiner, S., Kellerer, S., Bosl, M. R., Russell, S. and Wegner, M. (2010). Replacement of mouse Sox10 by the Drosophila ortholog Sox100B provides evidence for co-option of SoxE proteins into vertebrate-specific gene-regulatory networks through altered expression. Dev Biol 341(1): 267-281. PubMed ID: 20144603

DeFalco, T. J., Verney, G., Jenkins, A. B., McCaffery, J. M., Russell, S. and Van Doren, M. (2003). Sex-specific apoptosis regulates sexual dimorphism in the Drosophila embryonic gonad. Dev Cell 5(2): 205-216. PubMed ID: 12919673

Doupé, D. P., Marshall, O. J., Dayton, H., Brand, A. H. and Perrimon, N. (2018). Drosophila intestinal stem and progenitor cells are major sources and regulators of homeostatic niche signals. Proc Natl Acad Sci U S A 115(48): 12218-12223. PubMed ID: 30404917

Ikegami, D., Akiyama, H., Suzuki, A., Nakamura, T., Nakano, T., Yoshikawa, H. and Tsumaki, N. (2011). Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways. Development 138(8): 1507-1519. PubMed ID: 21367821

Hui Yong Loh, S. and Russell, S. (2000). A Drosophila group E Sox gene is dynamically expressed in the embryonic alimentary canal. Mech Dev 93(1-2): 185-188. PubMed ID: 10781954

Jin, Z., Chen, J., Huang, H., Wang, J., Lv, J., Yu, M., Guo, X., Zhang, Y., Cai, T. and Xi, R. (2020). The Drosophila ortholog of mammalian transcription factor Sox9 regulates intestinal homeostasis and regeneration at an appropriate level. Cell Rep 31(8): 107683. PubMed ID: 32460025

Lan, Q., Cao, M., Kollipara, R. K., Rosa, J. B., Kittler, R. and Jiang, H. (2018). FoxA transcription factor Fork head maintains the intestinal stem/progenitor cell identities in Drosophila. Dev Biol 433(2): 324-343. PubMed ID: 29108672

Liu, C. F. and Lefebvre, V. (2015). The transcription factors SOX9 and SOX5/SOX6 cooperate genome-wide through super-enhancers to drive chondrogenesis. Nucleic Acids Res 43(17): 8183-8203. PubMed ID: 26150426

Loh, H. Y. and Russell, S. (2000). A Drosophila group E Sox gene is dynamically expressed in the embryonic alimentary canal. Mech. Dev. 93(1-2): 185-188. 10781954

Meng, F. W. and Biteau, B. (2015). A Sox transcription factor is a critical regulator of adult stem cell proliferation in the Drosophila intestine. Cell Rep 13(5): 906-914. PubMed ID: 26565904

Meng, F. W., Rojas Villa, S. E. and Biteau, B. (2020). Sox100B Regulates Progenitor-Specific Gene Expression and Cell Differentiation in the Adult Drosophila Intestine. Stem Cell Reports 14(2): 226-240. PubMed ID: 32032550

Misra, S., Pandey, A. K., Gupta, S., Kumar, A., Khanna, P., Shankar, J. and Ravi Ram, K. (2017). Estrogen related receptor is required for the testicular development and for the normal sperm axoneme/mitochondrial derivatives in Drosophila males. Sci Rep 7: 40372. PubMed ID: 28094344

Mori-Akiyama, Y., van den Born, M., van Es, J. H., Hamilton, S. R., Adams, H. P., Zhang, J., Clevers, H. and de Crombrugghe, B. (2007). SOX9 is required for the differentiation of paneth cells in the intestinal epithelium. Gastroenterology 133(2): 539-546. PubMed ID: 17681175

Nanda, S., DeFalco, T. J., Loh, S. H., Phochanukul, N., Camara, N., Van Doren, M. and Russell, S. (2009). Sox100B, a Drosophila group E Sox-domain gene, is required for somatic testis differentiation. Sex Dev 3(1): 26-37. PubMed ID: 19339815

Oh, C. D., Lu, Y., Liang, S., Mori-Akiyama, Y., Chen, D., de Crombrugghe, B. and Yasuda, H. (2014). SOX9 regulates multiple genes in chondrocytes, including genes encoding ECM proteins, ECM modification enzymes, receptors, and transporters. PLoS One 9(9): e107577. PubMed ID: 25229425

Patel, P. H., Dutta, D. and Edgar, B. A. (2015). Niche appropriation by Drosophila intestinal stem cell tumours. Nat Cell Biol 17(9): 1182-1192. PubMed ID: 26237646

Shi, Z., Chiang, C. I., Labhart, P., Zhao, Y., Yang, J., Mistretta, T. A., Henning, S. J., Maity, S. N. and Mori-Akiyama, Y. (2015). Context-specific role of SOX9 in NF-Y mediated gene regulation in colorectal cancer cells. Nucleic Acids Res 43(13): 6257-6269. PubMed ID: 26040697

Zhai, Z., Kondo, S., Ha, N., Boquete, J. P., Brunner, M., Ueda, R. and Lemaitre, B. (2015). Accumulation of differentiating intestinal stem cell progenies drives tumorigenesis. Nat Commun 6: 10219. PubMed ID: 26690827

Zhai, Z., Boquete, J. P. and Lemaitre, B. (2017). A genetic framework controlling the differentiation of intestinal stem cells during regeneration in Drosophila. PLoS Genet 13(6): e1006854. PubMed ID: 28662029

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Biological Overview

date revised: 22 October 2020

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