InteractiveFly: GeneBrief

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Centrosomes are microtubule-organizing centers required for error-free mitosis and embryonic development. The microtubule-nucleating activity of centrosomes is conferred by the pericentriolar material (PCM), a composite of numerous proteins subject to cell cycle-dependent oscillations in levels and organization. In diverse cell types, mRNAs localize to centrosomes and may contribute to changes in PCM abundance. This study investigated the regulation of mRNA localization to centrosomes in the rapidly cycling Drosophila melanogaster embryo. RNA localization to centrosomes was found to be regulated during the cell cycle and developmentally. A novel role for the fragile-X mental retardation protein was identified in the posttranscriptional regulation of a model centrosomal mRNA, centrocortin (cen). Further, mistargeting cen mRNA is sufficient to alter cognate protein localization to centrosomes and impair spindle morphogenesis and genome stability (Ryder, 2020).

The centrosome is a multifunctional organelle that serves as the primary microtubule-organizing center of most animal cells and comprises a central pair of centrioles surrounded by a proteinaceous matrix of pericentriolar material (PCM). During mitosis, centrosomes help organize the bipolar mitotic spindle and function to ensure the fidelity of cell division. In interphase, centrosomes contribute to cell polarization, intracellular trafficking, and ciliogenesis (Ryder, 2020).

Cell cycle-dependent changes in PCM composition contribute to functional changes in centrosome activity. Upon mitotic entry, centrosomes undergo mitotic maturation, a process by which centrosomes augment their microtubule-nucleating capacity through the recruitment of additional PCM. This process is reversed upon mitotic exit by PCM shedding (Magescas, 2019; Mittasch, 2020). These dynamic oscillations in PCM composition and organization are essential for centrosome function, and their deregulation is associated with developmental disorders, increased genomic instability, and cancer. Nonetheless, the regulation of PCM dynamics remains incompletely understood (Ryder, 2020).

Centrosomes are essential for early Drosophila embryogenesis, which proceeds through 14 rounds of rapid, synchronous, abridged nuclear cycles (NCs) consisting of S and M phases with no intervening gap phases before cellularization. From NC 10 to 14, the embryo develops as a syncytial blastoderm, wherein thousands of nuclei and their associated centrosome pairs divide just under the embryonic cortex. Nuclear migration and divisions are coordinated by the centrosomes, and mutations in centrosome-associated genes impair spindle morphogenesis, mitotic synchrony, genome stability, and embryonic viability. As in many organisms, the early development of the Drosophila embryo proceeds through a period of transcriptional quiescence and is supported by a maternal supply of mRNA and proteins. Thus, PCM dynamics apparent in early embryos rely on posttranscriptional mechanisms (Ryder, 2020).

More than a decade ago, a high-throughput screen for mRNAs with distinct subcellular locations in syncytial Drosophila embryos uncovered a subset of mRNAs localizing to spindle poles (Lecuyer, 2007). Many of the centrosome-enriched transcripts identified in that screen encode known centrosome regulators, including cyclin B (cyc B) and pericentrin-like protein (plp). These findings raise the possibility that RNA localization, translational control, and other posttranscriptional regulatory mechanisms contribute to centrosome activity and/or function. Consistent with this idea, RNA is known to associate with centrosomes in diverse cell types, including early embryos (Drosophila, Xenopus, zebrafish, and mollusk), surf clams, and cultured mammalian cells. The functional consequences and the mechanisms that regulate centrosome-localized RNA remain little understood, however (Ryder, 2020).

This study reports that multiple RNAs dynamically localize to centrosomes in Drosophila early embryos. These RNAs localize in unique patterns, with some forming higher-order granules and others localizing to centrosomes as individual molecules. This study further demonstrates that some RNAs localize to centrosomal subdomains, e.g., centrosome flares, which extend from interphase centrosomes and define the PCM scaffold (Lerit, 2015; Megraw, 2002; Richens, 2015). This study has identified one centrosomal RNA, centrocortin (cen), which forms micrometer-scale granules that localize asymmetrically to centrosomes. This study further defines the mechanisms underlying cen mRNA granule formation and function. cen mRNA granules include Cen protein and the translational regulator fragile-X mental retardation protein (FMRP), the orthologue of the fragile X syndrome-related RNA-binding protein encoded by the Fmr1 gene. These data show that FMRP regulates both the localization and steady-state levels of cen RNA and protein. Moreover, this study found that reducing cen dosage is sufficient to ameliorate mitotic spindle defects associated with Fmr1 loss. Finally, mislocalization of cen mRNA was shown to prevent the localization of protein to distal centrosomes and is associated with disrupted embryonic nuclear divisions (Ryder, 2020).

This study systematically examined five transcripts shown to enrich near spindle poles to quantitatively define their common and unique localization patterns in Drosophila embryos. Subsets of mRNAs were identified showing centrosome enrichment in a cell cycle-regulated and developmentally regulated manner. These nonrandom variances in RNA distributions further imply biological relevance. Tests were performed to see if RNA localization contributes to normal centrosome functions through in-depth studies with a model transcript, cen mRNA. FMRP was identified as an RNA-binding protein required for regulation of cen RNA localization, organization, and translational control. Further, reducing cen dosage rescued Fmr1-dependent mitotic errors and embryonic lethality. The consequences of mistargeting cen mRNA were directly tested. Mislocalization of cen mRNA to the anterior abrogated the normal localization of Cen to more distal centrosomes and disrupted spindle organization. Anterior mitotic divisions were also severely disrupted due to the increased local concentration of cen mRNA, which also recruited FMRP. These studies suggest that a normalized local concentration of cen mRNA is essential for normal cell division and genome stability (Ryder, 2020).

FMRP is a multifunctional RNA-binding protein with roles in translational repression, activation, RNA localization, and RNA stability. In humans, mutations in the gene encoding FMRP, FMR1, are the leading cause of heritable intellectual disability and autism. Although high-throughput studies have identified putative RNA substrates, surprisingly few of these have been validated. The current studies demonstrate that cen mRNA is regulated by FMRP, either directly or indirectly, and that titrating cen dosage is sufficient to partially restore embryonic viability in Fmr1 mutants. Consistent with direct regulation of cen mRNA by FMRP, the cen coding sequence contains six putative binding motifs for FMRP, according to RBPmap, an RNA-binding motif predictor. Moreover, human orthologues of cen, CDR2 and CDR2L, were identified as direct FMRP targets (Ascano, 2012). Deregulation of CDR2 and CDR2L is associated with paraneoplastic cerebellar degeneration (Albert, 1998; Corradi, 1997). These studies suggest that Drosophila cen may serve as a valuable model to uncover mechanisms underlying FMRP-mediated regulation of CDR2 and CDR2L. Whether FMRP similarly regulates other centrosome-localized mRNAs is an interesting question for future study (Ryder, 2020).

The enhanced recruitment of cen mRNA to heterogeneously sized pericentrosomal granules, coupled with the increased production of Cen protein within Fmr1 mutants, led to a speculation that cen mRNA granules may be sites of local translation, as recently proposed (Bergalet, 2020). However, disruption of cen granule formation, as in cnnB4 mutants, does not impair total Cen protein levels. This finding raises the possibility that Cen may be translated at alternate sites or that maternal stores of Cen obscure changes resulting from cen mRNA granule loss. These models are not mutually exclusive, and cen mRNA may be translated at multiple locales. The data support a model in which centrosomes serve as platforms for translation control, which may be positive or negative depending on the specific transcript and/or cell cycle stage, consistent with the idea that cen mRNA granules are sites of Cen translational regulation (Bergalet, 2020; Ryder, 2020).

This study shows that cen mRNA preferentially localizes to interphase centrosomes; that the centrosome scaffold, Cnn, is required for cen mRNA granule formation and localization; and that FMRP functions as a negative regulator of cen mRNA, limiting cen mRNA stability and translation of Cen protein. It is speculated that FMRP represses Cen translation within cen mRNA granules, dampening the local Cen concentration. Consequently, cen mRNA enrichment at centrosomes is exaggerated in Fmr1 mutants. Other factors likely promote Cen translation. Translational repression or derepression may be coupled to cen mRNA granule centrosome proximity, which decreases as embryos enter mitosis. An imbalance of Cen levels at centrosomes, either too little (as in cen mutants) or too much (as in Fmr1 mutants or cen-bcd-3'UTR embryos), impairs centrosome function/spindle integrity and embryonic viability. As the cen 3'UTR recruits ik2 mRNA to centrosomes, the mitotic defects observed following cen perturbation may result from indirect effects via ik2 mRNA (Bergalet, 2020). Nonetheless, cen mRNA dosage must be properly regulated for mitotic fidelity (Ryder, 2020).

A common trend emerging from comparative analyses is the greater enrichment of mRNA at interphase versus metaphase centrosomes. One possible explanation is the differential size of interphase centrosomes, which are significantly larger in Drosophila embryos owing to the elaboration of extended centrosome flares, part of the architecture of the centrosome scaffold (Lerit, 2015; Megraw, 2002; Richens, 2015). This pattern contrasts with mammalian centrosomes, which are larger in mitosis. According to this size model, a larger centrosome might dock additional RNAs simply because of the increased volume it occupies in the cell. This model was discounted based on the finding that a highly expressed control transcript, gapdh, does not enrich at interphase centrosomes. This result also argues against the idea that centrosomes recruit RNA molecules spuriously. Relatively few RNAs localize to centrosomes. This study shows that the localization of centrosome-associated RNA is regulated in space and time (Ryder, 2020).

Why do RNAs localize to interphase centrosomes? Recent work in mammalian cells proposed that some lengthy transcripts may be cotranslationally transported to centrosomes (Chouaib, 2020; Sepulveda, 2018). This model would account for contemporaneous recruitment and colocalization of centrosome mRNA and proteins and may be pertinent to cen mRNA localization. Of the RNAs overlapping with the centrosome surface, sov was unique in that it appeared to preferentially dock along centrosome flares, localizing to the outer PCM zone. However, thus stydt did not detect Sov protein at centrosomes. Instead, Sov resides in the nucleus during interphase and is undetectable after nuclear envelope breakdown. These findings suggest that Sov is rapidly translocated into the nucleus. Live imaging of RNA transport and nascent protein synthesis is required to rigorously test the dynamics of RNA localization and local translation (Ryder, 2020).

Another model that may account for enrichment of centrosome RNAs at interphase centrosomes is the possibility that RNA contributes to centrosome structure, perhaps by promoting phase transitions. A common principle of phase transitions is the association of intrinsically disordered proteins with specific RNA molecules to form non-membrane-bound organelles with unique biophysical properties. Might cen mRNA granules represent phase-separated domains? Congruous with phase separation, Cen protein contains multiple predicted intrinsically disordered domains. While the contribution of all centrosomal RNAs cannot be ruled out, the current studies do not suggest that cen mRNA contributes to centrosome structure. Mistargeting cen mRNA to the anterior cortex did not appear to disrupt the organization of distal centrosomes, for example (Ryder, 2020).

Critically, disrupting the PCM scaffold is sufficient to inhibit formation of the cen mRNA granule. Previous work has shown that the PCM scaffold becomes progressively more structured during the prolonged interphases of later NCs. Additionally, the mother centrosome organizes a larger PCM scaffold owing to inherently greater levels of Cnn and PLP (Conduit, 2010; Lerit, 2015). Collectively, these features may account for the asymmetric localization of cen mRNA to mother centrosomes in late-stage syncytial embryos. These data lead to the conclusion that the PCM scaffold organized by Cnn and PLP is upstream of the recruitment and organization of cen mRNA granules (Ryder, 2020).

Many types of RNP granules form within cells, including stress granules, germ granules, P-bodies, etc., which all have unique functions and modes of assembly. The spatial proximity of multiple RNA molecules may facilitate intermolecular RNA interactions subsequently recognized by RNA-binding proteins. The FMRP-containing cen mRNA granule represents one such RNP, and further understanding how it promotes mitotic integrity warrants further investigation. As the early Drosophila embryo is transcriptionally quiescent, posttranscriptional regulatory mechanisms, and especially translational control, are fundamentally important for proper centrosome regulation and function (Ryder, 2020).

Inter-dependent centrosomal co-localization of the cen and ik2 cis-natural antisense mRNAs in Drosophila

Overlapping genes are prevalent in most genomes, but the extent to which this organization influences regulatory events operating at the post-transcriptional level remains unclear. Studying the cen and ik2 genes of Drosophila melanogaster, which are convergently transcribed as cis-natural antisense transcripts (cis-NATs) with overlapping 3' UTRs, it was found that their encoded mRNAs strikingly co-localize to centrosomes. These transcripts physically interact in a 3' UTR-dependent manner, and the targeting of ik2 requires its 3' UTR sequence and the presence of cen mRNA, which serves as the main driver of centrosomal co-localization. The cen transcript undergoes localized translation in proximity to centrosomes, and its localization is perturbed by polysome-disrupting drugs. By interrogating global fractionation-sequencing datasets generated from Drosophila and human cellular models, this study found that RNAs expressed as cis-NATs tend to co-localize to specific subcellular fractions. This work suggests that post-transcriptional interactions between RNAs with complementary sequences can dictate their localization fate in the cytoplasm (Bergalet, 2020).

Despite the realization that overlapping transcriptional units represent a pervasive feature of genomes, the biological and mechanistic significance of this organization remains incompletely understood. For instance, although NATs have been found to modulate gene expression at the transcriptional level, they can also impact post-transcriptional regulation, notably through the formation of double-stranded RNA, leading to RNA masking, RNA interference, or RNA editing. This study reports a post-transcriptional function of NATs in mRNA subcellular localization. Indeed, it was shown that the cen and ik2 mRNAs, two NATs expressed in Drosophila melanogaster, are tightly co-localized to centrosomes in the cytoplasm. It was further demonstrate that the centrosomal localization of ik2 is strictly dependent on cen mRNA and requires the 3' UTR overlapping region, which mediates their physical association. More generally, this analyses of subcellular transcriptomics datasets, either based on biochemical cell fractionation or proximity labeling, suggests that the co-localization of cis-NATs is a common occurrence in Drosophila and human cells (Bergalet, 2020).

Although several studies have shown that convergent transcription of NATs can lead to inhibitory interactions due to transcriptional interference, the current findings reveal an alternative scenario in which NATs can impose selectivity in downstream RNA subcellular localization behavior. Early Drosophila embryogenesis may offer a favorable environment for such a regulatory mechanism, considering the diverse RNA populations they contain of either maternal or zygotic origin. The cen and ik2 transcripts undergo co-localization as maternally provided transcripts in syncytial-stage embryos, after being transcribed from polyploid nurse cells prior to their deposition in the maturing oocyte. Although their 3' overlapping sequence is important for centrosomal targeting of ik2 mRNA, transgenic reporter assays revealed that a gfp-ik2-3'UTR reporter mRNA can undergo proper localization when expressed in trans from a different chromosome landing site. These results are consistent with a previous study in yeast, showing that transcriptional interference mediated by 3' overlapping transcripts could also occur in trans. The current findings thus suggest that, in addition to NATs, transcripts containing complementary sequences to other cellular RNAs may influence their subcellular localization properties. Interestingly, emergent methods used to define RNA-RNA interactomes have shown that trans interactions between mRNA molecules are prevalent in eukaryotic cells, which may profoundly influence post-transcriptional gene regulation, including RNA subcellular localization (Bergalet, 2020).

The number of RNA molecules that are present within RNA transport granules has remained a question of debate. Although some studies support the concept that messenger ribonucleoprotein (mRNP) granules contain single mRNA molecules, others have reported examples where such granules may contain multiple mRNA species. Previous studies have revealed a role for RNA-RNA interactions in localization control. Indeed, the bicoid and oskar mRNAs have been shown to localize as homo-dimers in Drosophila embryos and oocytes, respectively. The current results define an alternate mechanism of transcript co-targeting mediated by hetero-duplexing of distinct mRNA species, a process that is required to allow centrosomal targeting of ik2 mRNA in a cen-dependent manner. Although the data indicate that cen and ik2 co-localize at different subcellular locations during oogenesis and embryogenesis, it is unclear whether this involves a mechanism of co-transport within mobile ribonucleoprotein (RNP) granules or whether their observed centrosomal co-targeting involves ik2 mRNA capture by pre-localized cen transcripts. It is also unclear whether cen and ik2 centrosomal co-targeting is dependent on direct RNA-RNA interactions between these transcripts or whether their association is mediated by specific protein interactors. Future experiments will aim to clarify these different possibilities (Bergalet, 2020).

Several studies in different organisms have characterized mRNAs that are specifically localized to mitotic structures, leading to different models of the potential functional roles of this process. For example, work in Ilyanassa embryos showed that the asymmetric localization of mRNAs to centrosomes provides an elegant mechanism to drive the selective inheritance of specific transcripts between daughter cells during embryonic cleavage divisions. Other mitotic transcripts encode proteins with mitotic-related functions, implying that they may fulfill more active roles in cell division regulation via localized translation. The possibility of localized translation at the level of the mitotic apparatus is supported by various lines of evidence, including traditional electron microscopy approaches that revealed the presence of ribosome-like particles in proximity to the mitotic spindle and centrosomes, as well as more recent transcriptomic and mass-spectrometry-based approaches that co-purified various RNAs and RNA binding proteins with mitotic structures. The observations that cen and ik2 mRNAs, as well as their encoded proteins, display peri-centrosomal targeting, combined with the Puro-PLA results, suggest that they undergo localized translation. This would be consistent with the established role of Cen in regulating mitotic spindle and cleavage furrow function (Kao, 2009). Although Ik2 (also known as I-KappaB kinase Epsilon/IKK-E) has been implicated in various biological processes in Drosophila, including cytoskeleton regulation during oogenesis, endosome shuttling, and dendritic pruning, the current work uncovers a role of Ik2 in mitotic regulation, which it is speculated may have evolved through the localization properties of its mRNA. Taken together, these findings reveal a mechanism of co-dependent localization of two mRNA species that has been acquired during evolution via genomic sequence reorganization, leading to a potential acquisition of protein function. Understanding the spatial and temporal dynamics of the translation of centrosomal mRNAs will be an important area of future research (Bergalet, 2020).

Drosophila centrocortin is dispensable for centriole duplication but contributes to centrosome separation

Centrosomes are microtubule-organizing centers that duplicate exactly once to organize the bipolar mitotic spindle required for error-free mitosis. Prior work indicated that Drosophila centrocortin (cen) is required for normal centrosome separation, although a role in centriole duplication was not closely examined. Through time-lapse recordings of rapid syncytial divisions, this study monitored centriole duplication and the kinetics of centrosome separation in control vs cen null embryos. The data suggest that although cen is dispensable for centriole duplication, it contributes to centrosome separation (Mehta, 2022).

Centrocortin cooperates with centrosomin to organize Drosophila embryonic cleavage furrows

In the Drosophila early embryo, the centrosome coordinates assembly of cleavage furrows. Currently, the molecular pathway that links the centrosome and the cortical microfilaments is unknown. In centrosomin (cnn) mutants, in which the centriole forms but the centrosome pericentriolar material (PCM) fails to assemble, actin microfilaments are not organized into furrows at the syncytial cortex. Although CNN is required for centrosome assembly and function, little is known of its molecular activities. This study shows the novel protein Centrocortin, which associates with centrosomes and also with cleavage furrows in early embryos, is required for cleavage furrow assembly. CEN binds to CNN within CNN Motif 2 (CM2), a conserved 60 amino acid domain at CNN's C terminus. The cnn^B4 allele, which contains a missense mutation at a highly conserved residue within CM2, blocks the binding of CEN and disrupts cleavage furrow assembly. Together, these findings show that the C terminus of CNN coordinates cleavage furrow formation through binding to CEN, thereby providing a molecular link between the centrosome and cleavage furrow assembly (Kao, 2009).

To address the role of CEN in early embryos, the phenotype of a cen mutant was examined. A piggybac transposon insertion mutation within the coding sequence of cen at amino acid position 290 was available for this analysis. Maternal effect cen mutant embryos, collected from hemizygous cen^f04787 mutant mothers [cen^f04787 heterozygous with a deficiency chromosome, Df(2L)Fs(2)Ket^RX32, which deletes the cen locus], contained no detectable CEN protein by western blotting with antibodies directed against either the C or N terminus of CEN. A truncated protein product, predicted by the site of insertion of the transposon to be at least 33 kDa, was also not detected with the antibody directed against the amino terminus of CEN, which was raised against a polypeptide included within this truncation. Moreover, no CEN signal was detected at centrosomes or furrows in cen^f04787 embryos upon immunostaining with CEN antibodies (Kao, 2009).

Homozygous and hemizygous cen^f04787 mutants were viable and fertile. However, hemizygous cen^f04787 females laid eggs that failed to hatch at a significantly higher rate of 8.70% ± 0.50% compared to wild-type females (4.29% ± 0.42%). A cen transgene that expresses a cen cDNA, including the entire coding sequence with the 5'and 3' UTRs, rescued this hatch rate deficiency to the levels seen with wild-type females. Together, these data show that cen^f04787 is a cen mutation that reduces its expression to an undetectable level and affects embryonic development maternally (Kao, 2009).

To investigate CEN's role in centrosome and cleavage furrow function, hemizygous maternal cen^f04787 mutant embryos, hereafter referred to as cen^f04787 embryos, were stained for CNN, α-tubulin, and filamentous actin to examine centrosome and cytoskeleton organization during cleavage. In cen^f04787 embryos, mitotic spindles were frequently linked together, a phenotype also characteristic of cnn mutant embryos, as well as an indication of furrow assembly failure. Although the severity of linked spindles is variable among cen^f04787embryos, this phenotype is highly penetrant, with 30.77% (16/52) of metaphase cen^f04787 embryos showing linked spindles, compared to wild-type embryos. Actin staining showed that furrows form aberrantly, are consistently less robust, and have decreased furrow depth in cen^f04787 embryos. Actin organization into pseudocleavage furrows displayed variable degrees of disruption in cen^f04787 embryos; however, overall 28% of cen^f04787 embryos displayed broken or weak furrows at prophase or metaphase. In addition, the distribution of actin density in furrows was frequently irregular in cen^f04787 embryos, and patches of small furrows were common. However, no obvious effects on actin cap formation were observed at interphase. Thus, cen mutant embryos are deficient in mitotic cleavage furrow assembly. Although the furrow defects and linked spindles of cen^f04787 embryos are ~28%-31%, the embryo hatch failure rate is ~9%, only 5% higher than that of the wild-type, thereby attesting to the ability of embryos to cope with the furrow defects in cen mutant embryos, with the likely exception of those with very severe defects (Kao, 2009).

On the minority of wild-type spindles in which CEN appeared to split symmetrically between the two centrosomes at mitosis, no effect on furrow assembly was observed. This suggests that the asymmetry of CEN distribution at mitosis may not have any acute effect on furrow assembly. It is proposed that CEN localization at centrosomes may function early in mitosis to initiate a signaling process that is required as furrow assembly proceeds, thus impacting furrow actin assembly at mitotic furrows (Kao, 2009).

Recycling endosomes (REs) have a defined role in the trafficking of actin- and membrane-containing vesicles to organize cleavage furrows. To investigate an impact on RE function in cen^f04787 embryos, RE markers Nuf and Rab11, which localize to REs that are distributed in a pericentrosomal pattern, were stained. Localization of neither of these RE components nor the Dystrophin ortholog and furrow membrane protein Dah, which is very sensitive to perturbations of RE activity, was affected by loss of CEN function. Given that the REs activate Rho1 at furrows through RhoGEF2 recruitment to promote actin assembly, it therefore appears that CEN promotes actin assembly at furrows by a Rho-independent pathway (Kao, 2009).

The cleavage furrow defects seen in cen^f04787 embryos are probably not due to microtubule assembly defects because the astral microtubules in cen^f04787 embryos are comparable to those in the wild-type. Moreover, the pericentrosomal localization of Nuf and Rab11 are dependent upon microtubules; yet their localization appeared to be normal in cen^f04787 embryos (Kao, 2009).

The phenotypes seen in cen^f04787 embryos are consistent with CEN functioning in conjunction with CNN in the early embryo: mutations in cnn cause defective furrow assembly. However, the defects in these processes in cen^f04787 embryos are not as severe as those that occur in cnn mutants, including the hypomorphic cnn^B4 mutant. This suggests that CEN may not be the only factor involved in conveying the signal from the CM2 domain of CNN to cleavage furrows. Nevertheless, given that CNN^B4 localizes to centrosomes, albeit with an altered PCM pattern, the ability of CEN to localize to centrosomes in cnn^B4 embryos was examined. Consistent with the yeast two-hybrid interaction assay, CEN failed to localize detectably at cnn^B4 centrosomes and yet was localized variably at furrows during early cortical cycles (10 and 11), but not at the residual patches of furrows that form at later cycles (12 and 13) in cnn^B4 embryos. Because the interaction of CEN and CNN^B4 is reduced but not abolished, it is possible that some CEN is localized to centrosomes and that this facilitates the inefficient localization to cnn^B4 furrows. Alternatively, CEN association with CNN may be required for its activation prior to its action at furrows to promote actin assembly (Kao, 2009).

Together, these data indicate that the conserved domain at the C terminus of CNN is critical for cleavage furrow formation and for recruitment of CEN to centrosomes. However, because furrow defects in the cen mutant are not as severe as cnn^B4, CEN is unlikely to be the only factor involved in the regulation of furrow formation by CNN CM2. In summary, CNN CM2 instructs cleavage furrow formation and appears to accomplish this in part through the recruitment of CEN to the centrosome and/or directing it to the cleavage furrow (Kao, 2009).

In conclusion, the CM2 domain of CNN is required for the signaling from the centrosome to instruct cleavage furrow assembly at the embryonic cortical membrane. CM2 accomplishes this through binding with CEN, which is required for efficient cleavage furrow formation. Thus, the CM2 domain of CNN and CEN represent a molecular link between centrosomes and the signals that regulate cleavage furrow assembly (Kao, 2009).

Search PubMed for articles about Drosophila Centrocortin

Albert, M. L., Darnell, J. C., Bender, A., Francisco, L. M., Bhardwaj, N. and Darnell, R. B. (1998). Tumor-specific killer cells in paraneoplastic cerebellar degeneration. Nat Med 4(11): 1321-1324. PubMed ID: 9809559

Ascano, M., Jr., Mukherjee, N., Bandaru, P., Miller, J. B., Nusbaum, J. D., Corcoran, D. L., Langlois, C., Munschauer, M., Dewell, S., Hafner, M., Williams, Z., Ohler, U. and Tuschl, T. (2012). FMRP targets distinct mRNA sequence elements to regulate protein expression. Nature 492(7429): 382-386. PubMed ID: 23235829

Bergalet, J., Patel, D., Legendre, F., Lapointe, C., Benoit Bouvrette, L. P., Chin, A., Blanchette, M., Kwon, E. and Lecuyer, E. (2020). Inter-dependent centrosomal co-localization of the cen and ik2 cis-natural antisense mRNAs in Drosophila. Cell Rep 30(10): 3339-3352. PubMed ID: 32160541

Chouaib, R., Safieddine, A., Pichon, X., Imbert, A., Kwon, O. S., Samacoits, A., Traboulsi, A. M., Robert, M. C., Tsanov, N., Coleno, E., Poser, I., Zimmer, C., Hyman, A., Le Hir, H., Zibara, K., Peter, M., Mueller, F., Walter, T. and Bertrand, E. (2020). A dual protein-mRNA localization screen reveals compartmentalized translation and widespread co-translational RNA targeting. Dev Cell 54(6): 773-791 e775. PubMed ID: 32783880

Conduit, P. T., Brunk, K., Dobbelaere, J., Dix, C. I., Lucas, E. P. and Raff, J. W. (2010). Centrioles regulate centrosome size by controlling the rate of Cnn incorporation into the PCM. Curr Biol 20(24): 2178-2186. PubMed ID: 21145741

Corradi, J. P., Yang, C., Darnell, J. C., Dalmau, J. and Darnell, R. B. (1997). A post-transcriptional regulatory mechanism restricts expression of the paraneoplastic cerebellar degeneration antigen cdr2 to immune privileged tissues. J Neurosci 17(4): 1406-1415. PubMed ID: 9006982

Kao, L. R. and Megraw, T. L. (2009). Centrocortin cooperates with centrosomin to organize Drosophila embryonic cleavage furrows. Curr Biol 19(11): 937-942. PubMed ID: 19427213

Lecuyer, E., Yoshida, H., Parthasarathy, N., Alm, C., Babak, T., Cerovina, T., Hughes, T. R., Tomancak, P. and Krause, H. M. (2007). Global analysis of mRNA localization reveals a prominent role in organizing cellular architecture and function. Cell 131(1): 174-187. PubMed ID: 17923096

Lerit, D. A., Jordan, H. A., Poulton, J. S., Fagerstrom, C. J., Galletta, B. J., Peifer, M. and Rusan, N. M. (2015). Interphase centrosome organization by the PLP-Cnn scaffold is required for centrosome function. J Cell Biol 210(1): 79-97. PubMed ID: 26150390

Magescas, J., Zonka, J. C. and Feldman, J. L. (2019). A two-step mechanism for the inactivation of microtubule organizing center function at the centrosome. Elife 8. PubMed ID: 31246171

Megraw, T. L., Kilaru, S., Turner, F. R. and Kaufman, T. C. (2002). The centrosome is a dynamic structure that ejects PCM flares. J Cell Sci 115(Pt 23): 4707-4718. PubMed ID: 12415014

Mehta, D. S., Zein-Sabatto, H., Ryder, P. V., Lee, J. and Lerit, D. A. (2022). Drosophila centrocortin is dispensable for centriole duplication but contributes to centrosome separation. G3 (Bethesda) 12(2). PubMed ID: 35100335

Mittasch, M., Tran, V. M., Rios, M. U., Fritsch, A. W., Enos, S. J., Ferreira Gomes, B., Bond, A., Kreysing, M. and Woodruff, J. B. (2020). Regulated changes in material properties underlie centrosome disassembly during mitotic exit. J Cell Biol 219(4). PubMed ID: 32050025

Richens, J. H., Barros, T. P., Lucas, E. P., Peel, N., Pinto, D. M., Wainman, A. and Raff, J. W. (2015). The Drosophila Pericentrin-like-protein (PLP) cooperates with Cnn to maintain the integrity of the outer PCM. Biol Open 4(8): 1052-1061. PubMed ID: 26157019

Ryder, P. V., Fang, J. and Lerit, D. A. (2020). centrocortin RNA localization to centrosomes is regulated by FMRP and facilitates error-free mitosis. J Cell Biol 219(12). PubMed ID: 33196763

Sepulveda, G., Antkowiak, M., Brust-Mascher, I., Mahe, K., Ou, T., Castro, N. M., Christensen, L. N., Cheung, L., Jiang, X., Yoon, D., Huang, B. and Jao, L. E. (2018). Co-translational protein targeting facilitates centrosomal recruitment of PCNT during centrosome maturation in vertebrates. Elife 7. PubMed ID: 29708497

date revised: 18 January 2021

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