What's hot today: Current papers in developmental biology and gene function

What's hot today:
Current papers in developmental biology and gene function

Thursday, April 30th, 2020 - Behavior

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Smith, B. R. and Macdonald, S. J. (2020). Dissecting the Genetic Basis of Variation in Drosophila Sleep Using a Multiparental QTL Mapping Resource. Genes (Basel) 11(3). PubMed ID: 32168738
Summary:
There is considerable variation in sleep duration, timing and quality in human populations, and sleep dysregulation has been implicated as a risk factor for a range of health problems. Human sleep traits are known to be regulated by genetic factors, but also by an array of environmental and social factors. These uncontrolled, non-genetic effects complicate powerful identification of the loci contributing to sleep directly in humans. The model system, Drosophila melanogaster, exhibits a behavior that shows the hallmarks of mammalian sleep, and this study used a multitiered approach, encompassing high-resolution QTL mapping, expression QTL data, and functional validation with RNAi to investigate the genetic basis of sleep under highly controlled environmental conditions. A battery of sleep phenotypes was measured in >750 genotypes derived from a multiparental mapping panel and identified several, modest-effect QTL contributing to natural variation for sleep. Merging sleep QTL data with a large head transcriptome eQTL mapping dataset from the same population allowed refining the list of plausible candidate causative sleep loci. This set includes genes with previously characterized effects on sleep and circadian rhythms, in addition to novel candidates. Finally, adult, nervous system-specific RNAi was used on the Dopa decarboxylase, dyschronic, and timeless genes, finding significant effects on sleep phenotypes for all three. The genes resolved in this study are strong candidates to harbor causative, regulatory variation contributing to sleep.

Singh, P. and Donlea, J. M. (2020). Bidirectional regulation of sleep and synapse pruning after neural injury. Curr Biol. PubMed ID: 32142703
Summary:
Following acute neural injury, severed axons undergo programmed Wallerian degeneration over several following days. While sleep has been linked with synaptic reorganization under other conditions, the role of sleep in responses to neural injuries remains poorly understood. To study the relationship between sleep and neural injury responses, Drosophila melanogaster was examined following the removal of antennae or other sensory tissues. Daytime sleep is elevated after antennal or wing injury, but sleep returns to baseline levels within 24 h after injury. Similar increases in sleep are not observed when olfactory receptor neurons are silenced or when other sensory organs are severed, suggesting that increased sleep after injury is not attributed to sensory deprivation, nociception, or generalized inflammatory responses. Neuroprotective disruptions of the E3 ubiquitin ligase highwire and c-Jun N-terminal kinase basket in olfactory receptor neurons weaken the sleep-promoting effects of antennal injury, suggesting that post-injury sleep may be influenced by the clearance of damaged neurons. Finally, pre-synaptic active zones were shown to be preferentially removed from severed axons within hours after injury, and depriving recently injured flies of sleep slows the removal of both active zones and damaged axons. These data support a bidirectional interaction between sleep and synapse pruning after antennal injury: locally increasing the need to clear neural debris is associated with increased sleep, which is required for efficient active zone removal after injury.

Palavalli-Nettimi, R. and Theobald, J. C. (2020). Small eyes in dim light: Implications to spatio-temporal visual abilities in Drosophila melanogaster. Vision Res 169: 33-40. PubMed ID: 32163744
Summary:
Fruit flies, Drosophila melanogaster, are active over a range of light intensities in the wild, but lab-reared flies are often tested only in bright light. Similarly, scarce feeding during larval stages-common in nature-generates smaller adults, and a wide range of eye sizes not found in well-fed lab colonies. Both dimmer light and smaller eyes limit light capture and have undetermined effects on visual behaviors such as flight. This study used moving sinusoidal gratings to test spatial acuity, temporal acuity, and contrast threshold of female flies of varying eye sizes at different light intensities. Vision was also tested in the smaller and often neglected male fruit flies. As light intensity drops from 50.1 lx to 0.3 lx, flies have a reduced spatial acuity (females: from 0.1 to 0.06 cycles per degree, CPD, males: 0.1 to 0.04 CPD) and temporal acuity (females: from 50 Hz to 10 Hz, males: 25 Hz to 10 Hz), and an increased contrast detection threshold (females: from 10% to 29%, males: 19% to 48%). No major sex-specific differences were found after accounting for eye size. Visual abilities in both small (eye area of 0.1-0.17 mm(2)) and large flies (0.17-0.23 mm(2)) suffer at 0.3 lx compared to 50.1 lx, but small flies suffer more (spatial acuity: 0.03 vs 0.06 CPD, contrast threshold: 76% vs 57%, temporal acuity: 5 Hz vs 10 Hz). These results suggest visual abilities of small flies suffer more than large flies at low light levels, possibly leading to size- and light intensity-dependent effects on foraging, navigation, and flight.

Brown, E. B., Shah, K. D., Faville, R., Kottler, B. and Keene, A. C. (2020). Drosophila insulin-like peptide 2 mediates dietary regulation of sleep intensity. PLoS Genet 16(3): e1008270. PubMed ID: 32160200
Summary:
Sleep is a nearly universal behavior that is regulated by diverse environmental stimuli and physiological states. A defining feature of sleep is a homeostatic rebound following deprivation, where animals compensate for lost sleep by increasing sleep duration and/or sleep depth. The fruit fly, Drosophila melanogaster, exhibits robust recovery sleep following deprivation and represents a powerful model to study neural circuits regulating sleep homeostasis. Numerous neuronal populations have been identified in modulating sleep homeostasis as well as depth, raising the possibility that the duration and quality of recovery sleep is dependent on the environmental or physiological processes that induce sleep deprivation. This study finds that unlike most pharmacological and environmental manipulations commonly used to restrict sleep, starvation potently induces sleep loss without a subsequent rebound in sleep duration or depth. Both starvation and a sucrose-only diet result in increased sleep depth, suggesting that dietary protein is essential for normal sleep depth and homeostasis. Finally, Drosophila insulin like peptide 2 (Dilp2) was found to be acutely required for starvation-induced changes in sleep depth without regulating the duration of sleep. Flies lacking Dilp2 exhibit a compensatory sleep rebound following starvation-induced sleep deprivation, suggesting Dilp2 promotes resiliency to sleep loss. Together, these findings reveal innate resilience to starvation-induced sleep loss and identify distinct mechanisms that underlie starvation-induced changes in sleep duration and depth.

Slankster, E., Kollala, S., Baria, D., Dailey-Krempel, B., Jain, R., Odell, S. R. and Mathew, D. (2020). Mechanism underlying starvation-dependent modulation of olfactory behavior in Drosophila larva. Sci Rep 10(1): 3119. PubMed ID: 32080342
Summary:
Starvation enhances olfactory sensitivity that encourage animals to search for food. The molecular mechanisms that enable sensory neurons to remain flexible and adapt to a particular internal state remain poorly understood. The roles of GABA and insulin signaling in starvation-dependent modulation of olfactory sensory neuron (OSN) function was studied in the Drosophila larva. The GABAB-receptor and insulin-receptor play important roles during OSN modulation. Using an OSN-specific gene expression analysis, this study explored downstream targets of insulin signaling in OSNs. The results suggest that insulin and GABA signaling pathways interact within OSNs and modulate OSN function by impacting olfactory information processing. It was further shown that manipulating these signaling pathways specifically in the OSNs impact larval feeding behavior and its body weight. These results challenge the prevailing model of OSN modulation and highlight opportunities to better understand OSN modulation mechanisms and their relationship to animal physiology.

Kerwin, P., Yuan, J. and von Philipsborn, A. C. (2020). Female copulation song is modulated by seminal fluid. Nat Commun 11(1): 1430. PubMed ID: 32188855
Summary:
In most animal species, males and females communicate during sexual behavior to negotiate reproductive investments. Pre-copulatory courtship may settle if copulation takes place, but often information exchange and decision-making continue beyond that point. This study shows that female Drosophila sing by wing vibration in copula. This copulation song is distinct from male courtship song and requires neurons expressing the female sex determination factor DoublesexF. Copulation song depends on transfer of seminal fluid components of the male accessory gland. Hearing female copulation song increases the reproductive success of a male when he is challenged by competition, suggesting that auditory cues from the female modulate male ejaculate allocation. These findings reveal an unexpected fine-tuning of reproductive decisions during a multimodal copulatory dialog. The discovery of a female-specific acoustic behavior sheds new light on Drosophila mating, sexual dimorphisms of neuronal circuits and the impact of seminal fluid molecules on nervous system and behavior.

Wednesday, April 29th, Gonads

Jevitt, A., Chatterjee, D., Xie, G., Wang, X. F., Otwell, T., Huang, Y. C. and Deng, W. M. (2020). A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis. PLoS Biol 18(4): e3000538. PubMed ID: 32339165
Summary:
Oogenesis is a complex developmental process that involves spatiotemporally regulated coordination between the germline and supporting, somatic cell populations. This process has been modeled extensively using the Drosophila ovary. Although different ovarian cell types have been identified through traditional means, the large-scale expression profiles underlying each cell type remain unknown. Using single-cell RNA sequencing technology, this study has built a transcriptomic data set for the adult Drosophila ovary and connected tissues. Using this data set, the transcriptional trajectory was identified of the entire follicle-cell population over the course of their development from stem cells to the oogenesis-to-ovulation transition. This study further identified expression patterns during essential developmental events that take place in somatic and germline cell types such as differentiation, cell-cycle switching, migration, symmetry breaking, nurse-cell engulfment, egg-shell formation, and corpus luteum signaling. Extensive experimental validation of unique expression patterns in both ovarian and nearby, nonovarian cells also led to the identification of many new cell type-and stage-specific markers. The inclusion of several nearby tissue types in this data set also led to identification of functional convergence in expression between distantly related cell types such as the immune-related genes that were similarly expressed in immune cells (hemocytes) and ovarian somatic cells (stretched cells) during their brief phagocytic role in nurse-cell engulfment. Taken together, these findings provide new insight into the temporal regulation of genes in a cell-type specific manner during oogenesis and begin to reveal the relatedness in expression between cell and tissues types.

Schotthofer, S. K. and Bohrmann, J. (2020). Bioelectrical and cytoskeletal patterns correlate with altered axial polarity in the follicular epithelium of the Drosophila mutant gurken. BMC Dev Biol 20(1): 5. PubMed ID: 32169045
Summary:
Bioelectrical signals are known to be involved in the generation of cell and tissue polarity as well as in cytoskeletal dynamics. The epithelium of Drosophila ovarian follicles is a suitable model system for studying connections between electrochemical gradients, patterns of cytoskeletal elements and axial polarity. By interactions between soma and germline cells, the transforming growth factor-alpha homolog Gurken (Grk) establishes both the anteroposterior and the dorsoventral axis during oogenesis. In the follicular epithelium of the wild-type (wt) and the polarity mutant grk, stage-specific gradients of membrane potentials (Vmem) and intracellular pH (pHi) were analyzed using the potentiometric dye DiBAC4(3) and the fluorescent pH-indicator 5-CFDA,AM, respectively. Corresponding to impaired polarity in grk, the slope of the anteroposterior Vmem-gradient in stage S9 is significantly reduced compared to wt. Even more striking differences in Vmem- and pHi-patterns become obvious during stage S10B, when the respective dorsoventral gradients are established in wt but not in grk. Concurrent with bioelectrical differences, wt and grk exhibit differences concerning cytoskeletal patterns in the follicular epithelium. During all vitellogenic stages, basal microfilaments in grk are characterised by transversal alignment, while wt-typical condensations in centripetal follicle cells (S9) and in dorsal centripetal follicle cells (S10B) are absent. Moreover, in grk, longitudinal alignment of microtubules occurs throughout vitellogenesis in all follicle cells, whereas in wt, microtubules in mainbody and posterior follicle cells exhibit a more cell-autonomous organisation. Therefore, in contrast to wt, the follicular epithelium in grk is characterised by missing or shallower electrochemical gradients and by more coordinated transcellular cytoskeletal patterns. These results show that bioelectrical polarity and cytoskeletal polarity are closely linked to axial polarity in both wt and grk.

Thestrup, J., Tipold, M., Kindred, A., Stark, K., Curry, T. and Lewellyn, L. (2020). The Arp2/3 complex and the formin, Diaphanous, are both required to regulate the size of germline ring canals in the developing egg chamber. Dev Biol. PubMed ID: 31945342
Summary:
Intercellular bridges are an essential structural feature found in both germline and somatic cells throughout the animal kingdom. Because of their large size, the germline intercellular bridges, or ring canals, in the developing fruit fly egg chamber are an excellent model to study the formation, stabilization, and growth of these structures. Within the egg chamber, the germline ring canals connect 15 supporting nurse cells to the developing oocyte, facilitating the transfer of materials required for successful oogenesis. The ring canals are derived from a stalled actomyosin contractile ring; once formed, additional actin and actin-binding proteins are recruited to the ring to support the 20-fold growth that accompanies oogenesis. These behaviors provide a unique model system to study the actin regulators that control incomplete cytokinesis, intercellular bridge formation, and growth. By temporally controlling their expression in the germline, this study has demonstrated that the Arp2/3 complex and the formin, Diaphanous (Dia), coordinately regulate ring canal size and growth throughout oogenesis. Dia is required for successful incomplete cytokinesis and the initial stabilization of the germline ring canals. Once ring canals have formed, the Arp2/3 complex and Dia cooperate to determine ring canal size and maintain stability. These data suggest that nurse cells must maintain a precise balance between the activity of these two nucleators during oogenesis.

Lu, D., Sin, H. S., Lu, C. and Fuller, M. T. (2020). Developmental regulation of cell type-specific transcription by novel promoter-proximal sequence elements. Genes Dev. PubMed ID: 32217666
Summary:
Cell type-specific transcriptional programs that drive differentiation of specialized cell types are key players in development and tissue regeneration. One of the most dramatic changes in the transcription program in Drosophila occurs with the transition from proliferating spermatogonia to differentiating spermatocytes, with >3000 genes either newly expressed or expressed from new alternative promoters in spermatocytes. This study shows that opening of these promoters from their closed state in precursor cells requires function of the spermatocyte-specific tMAC complex (see always early ), localized at the promoters. The spermatocyte-specific promoters lack the previously identified canonical core promoter elements except for the Inr. Instead, these promoters are enriched for the binding site for the TALE-class homeodomain transcription factors Achi/Vis and for a motif originally identified under tMAC ChIP-seq peaks. The tMAC motif resembles part of the previously identified 14-bp beta2UE1 element critical for spermatocyte-specific expression. Analysis of downstream sequences relative to transcription start site usage suggested that ACA and CNAAATT motifs at specific positions can help promote efficient transcription initiation. These results reveal how promoter-proximal sequence elements that recruit and are acted upon by cell type-specific chromatin binding complexes help establish a robust, cell type-specific transcription program for terminal differentiation.

Shi, Z., Lim, C., Tran, V., Cui, K., Zhao, K. and Chen, X. (2020). Single-cyst transcriptome analysis of Drosophila male germline stem cell lineage. Development. PubMed ID: 32122991
Summary:
The Drosophila male germline stem cell (GSC) lineage provides a great model to understand stem cell maintenance, proliferation, differentiation, and dedifferentiation. This study used Drosophila GSC lineage to systematically analyze transcriptome of discrete but continuous differentiating germline cysts. First single cysts were isolated at each recognizable stage from wild-type testes, which were subsequently applied for RNA-seq analyses. The data delineate a high-resolution transcriptome atlas in the entire male GSC lineage: The most dramatic switch occurs from early to late spermatocyte, followed by the change from the mitotic spermatogonia to early meiotic spermatocyte. By contrast, the transit-amplifying spermatogonia cysts display similar transcriptomes, suggesting common molecular features among these stages, which may underlie their similar behavior during both differentiation and dedifferentiation processes. Finally, distinct differentiating germ cell cyst samples do not exhibit obvious dosage compensation of X-chromosomal genes, even with consideration of the paucity of X-chromosomal gene expression during meiosis, which is different from somatic cells. Together, the single cyst-resolution, genome-wide transcriptional profile analyses provide an unprecedented resource to understand many questions in both germ cell biology and stem cell biology fields.

Hafezi, Y., Sruba, S. R., Tarrash, S. R., Wolfner, M. F. and Clark, A. G. (2020). Dissecting Fertility Functions of Drosophila Y Chromosome Genes with CRISPR. Genetics. PubMed ID: 32098759
Summary:
Gene-poor, repeat-rich regions of the genome are poorly understood and have been understudied due to technical challenges and the misconception that they are degenerating "junk". The approximately 40 Mb Y chromosome of Drosophila melanogaster contains only 16 known protein-coding genes and is highly repetitive and entirely heterochromatic. Most of the genes originated from duplication of autosomal genes and have reduced nonsynonymous substitution rates, suggesting functional constraint. This study devised a genetic strategy for recovering and retaining stocks with sterile Y-linked mutations and combined it with CRISPR to create mutants with deletions that disrupt three Y-linked genes. Two genes, PRY and FDY, had no previously identified functions. PRY mutant males are sub-fertile, but FDY mutant males had no detectable fertility defects. FDY, the newest known gene on the Y chromosome, may have fertility effects that are conditional or too subtle to detect. The third gene, CCY, had been predicted but never formally shown to be required for male fertility. CRISPR-targeting and RNAi of CCY caused male sterility. Surprisingly, however, the CCY mutants were sterile even in the presence of an extra wild-type Y chromosome, suggesting that perturbation of the Y chromosome can lead to dominant sterility. This approach provides an important step toward understanding the complex functions of the Y chromosome and parsing which functions are accomplished by genes versus repeat elements.

Tuesday, April 28th - Adult Neural Function

Silva, B., Hidalgo, S. and Campusano, J. M. (2020). Dop1R1, a type 1 dopaminergic receptor expressed in Mushroom Bodies, modulates Drosophila larval locomotion. PLoS One 15(2): e0229671. PubMed ID: 32101569
Summary:
As in vertebrates, dopaminergic neural systems are key regulators of motor programs in insects, including the fly Drosophila melanogaster. Dopaminergic systems innervate the Mushroom Bodies (MB), an important association area in the insect brain primarily associated to olfactory learning and memory, but that has been also implicated with the execution of motor programs. The main objectives of this work is to assess the idea that dopaminergic systems contribute to the execution of motor programs in Drosophila larvae, and then, to evaluate the contribution of specific dopaminergic receptors expressed in MB to these programs. The results show that animals bearing a mutation in the dopamine transporter show reduced locomotion, while mutants for the dopaminergic biosynthetic enzymes or the dopamine receptor Dop1R1 exhibit increased locomotion. Pan-neuronal expression of an RNAi for the Dop1R1 confirmed these results. Further studies show that animals expressing the RNAi for Dop1R1 in the entire MB neuronal population or only in the MB gamma-lobe forming neurons, exhibit an increased motor output, as well. Interestingly, these results also suggest that other dopaminergic receptors do not contribute to larval motor behavior. Thus, the data support the proposition that CNS dopamine systems innervating MB neurons modulate larval locomotion and that Dop1R1 mediates this effect.

Ly, P. T. and Wang, H. (2020). Fzr/Cdh1 Promotes the Differentiation of Neural Stem Cell Lineages in Drosophila. Front Cell Dev Biol 8: 60. PubMed ID: 32117986
Summary:
How stem cells and progenitors balance between self-renewal and differentiation is a central issue of stem cell biology. This study describes a novel and essential function of Drosophila Fzr/Cdh1, an evolutionary conserved protein, during the differentiation of neural stem cell (NSC) lineages in the central nervous system. This study shows that Fzr, a known co-activator of Anaphase Promoting Complex/Cyclosome (APC/C) ubiquitin ligase, promotes the production of neurons from neural progenitors called ganglion mother cells (GMCs). However, knockdown of APC/C subunit Ida or another APC/C co-activator CDC20 does not similarly impair GMC-neuron transition. A concomitant loss of differentiation factor Prospero expression was observed, and ectopic accumulation of mitotic kinase Polo in fzr mutant clones, strongly supporting the impairment of GMC to neuron differentiation. Besides functioning in GMCs, Fzr is also present in NSCs to facilitate the production of intermediate neural progenitors from NSCs. Taken together, Fzr plays a novel function in promoting differentiation programs during Drosophila NSC lineage development. Given that human Fzr is inactivated in multiple types of human cancers including brain tumors and that Fzr regulates neurotoxicity in various models of neurodegenerative diseases, this study on the role of Fzr in turning off proliferation in neuronal cells may provide insights into how Fzr deficits may contribute to human neurodegenerative diseases and tumors.

Petruccelli, E., Brown, T., Waterman, A., Ledru, N. and Kaun, K. R. (2020). Alcohol Causes Lasting Differential Transcription in Drosophila Mushroom Body Neurons. Genetics. PubMed ID: 32132098
Summary:
Repeated alcohol experiences can produce long-lasting memories for sensory cues associated with intoxication. These memories can problematically trigger relapse in individuals recovering from alcohol use disorder (AUD). The molecular mechanisms by which ethanol changes memories to become long-lasting and inflexible remain unclear. New methods to analyze gene expression within precise neuronal cell-types can provide further insight towards AUD prevention and treatment. This study used genetic tools in Drosophila melanogaster to investigate the lasting consequences of ethanol on transcription in memory-encoding neurons. Drosophila rely on mushroom body (MB) neurons to make associative memories, including memories of ethanol-associated sensory cues. Differential expression analyses revealed that distinct transcripts, but not genes, in the MB were associated with experiencing ethanol alone compared to forming a memory of an odor cue associated with ethanol. Adult MB specific knockdown of spliceosome-associated proteins demonstrated the necessity of RNA processing in ethanol memory formation. These findings highlight the dynamic, context-specific regulation of transcription in cue-encoding neurons, and the lasting impact of ethanol on transcript usage during memory formation.

Nye, D. M. R., Albertson, R. M., Weiner, A. T., Hertzler, J. I., Shorey, M., Goberdhan, D. C. I., Wilson, C., Janes, K. A. and Rolls, M. M. (2020). The receptor tyrosine kinase Ror is required for dendrite regeneration in Drosophila neurons. PLoS Biol 18(3): e3000657. PubMed ID: 32163406
Summary:
While many regulators of axon regeneration have been identified, very little is known about mechanisms that allow dendrites to regenerate after injury. Using a Drosophila model of dendrite regeneration, a candidate screen was performed of receptor tyrosine kinases (RTKs), and a requirement was found for RTK-like orphan receptor (Ror). This study confirmed that Ror was required for regeneration in two different neuron types using RNA interference (RNAi) and mutants. Ror was not required for axon regeneration or normal dendrite development, suggesting a specific role in dendrite regeneration. Ror can act as a Wnt coreceptor with frizzleds (fzs) in other contexts, so this study tested the involvement of Wnt signaling proteins in dendrite regeneration. Knockdown of fz, dishevelled (dsh), Axin, and gilgamesh (gish) also reduced dendrite regeneration. Moreover, Ror was required to position Dsh and Axin in dendrites. Recently studies found that Wnt signaling proteins, including Dsh and Axin, localize microtubule nucleation machinery in dendrites. It is therefore hypothesized that Ror may act by regulating microtubule nucleation at baseline and during dendrite regeneration. Consistent with this hypothesis, localization of the core nucleation protein gammaTubulin was reduced in Ror RNAi neurons, and this effect was strongest during dendrite regeneration. In addition, dendrite regeneration was sensitive to partial reduction of gammaTubulin. It is conclude that Ror promotes dendrite regeneration as part of a Wnt signaling pathway that regulates dendritic microtubule nucleation.

Luo, J., Ting, C. Y., Li, Y., McQueen, P., Lin, T. Y., Hsu, C. P. and Lee, C. H. (2020). Antagonistic regulation by insulin-like peptide and activin ensures the elaboration of appropriate dendritic field sizes of amacrine neurons. Elife 9. PubMed ID: 32175842
Summary:
Establishing appropriate sizes and shapes of dendritic arbors is critical for proper wiring of the central nervous system. This study reports that Insulin-like Peptide 2 (DILP2) locally activates transiently expressed insulin receptors in the central dendrites of Drosophila Dm8 amacrine neurons to positively regulate dendritic field elaboration. DILP2 is expressed in L5 lamina neurons, which have axonal terminals abutting Dm8 dendrites. Proper Dm8 dendrite morphogenesis and synapse formation required insulin signaling through TOR (target of rapamycin) and SREBP (sterol regulatory element-binding protein), acting in parallel with previously identified negative regulation by Activin signaling to provide robust control of Dm8 dendrite elaboration. A simulation of dendritic growth revealed trade-offs between dendritic field size and robustness when branching and terminating kinetic parameters were constant, but dynamic modulation of the parameters could mitigate these trade-offs. It is suggested that antagonistic DILP2 and Activin signals from different afferents appropriately size Dm8 dendritic fields.

Muha, V., Fenckova, M., Ferenbach, A. T., Catinozzi, M., Eidhof, I., Storkebaum, E., Schenck, A. and van Aalten, D. M. F. (2020). O-GlcNAcase contributes to cognitive function in Drosophila. J Biol Chem. PubMed ID: 32094227
Summary:
O-GlcNAcylation is an abundant post-translational modification in neurons. In mice, an increase in O-GlcNAcylation leads to defects in hippocampal synaptic plasticity and learning. O-GlcNAcylation is established by two opposing enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). To investigate the role of OGA in elementary learning, this study generated catalytically inactive and precise knock-out Oga alleles (Oga(D133N) and Oga(KO), respectively) in Drosophila melanogaster. Adult Oga(D133N) and Oga(KO) flies lacking O-GlcNAcase activity showed locomotor phenotypes. Importantly, both Oga lines exhibited deficits in habituation, an evolutionary conserved form of learning, highlighting that the requirement for O-GlcNAcase activity for cognitive function is preserved across species. Loss of O-GlcNAcase affected number of synaptic boutons at the axon terminals of larval neuromuscular junction. Taken together, this study report behavioral and neurodevelopmental phenotypes associated with Oga alleles and show that Oga contributes to cognition and synaptic morphology in Drosophila.

Monday, April 27th - Physiology

Petersen, C. E., Wolf, M. J. and Smyth, J. T. (2020). Suppression of store-operated calcium entry causes dilated cardiomyopathy of the Drosophila heart. Biol Open 9(3). PubMed ID: 32086252
Summary:
Store-operated Ca(2+) entry (SOCE) is an essential Ca(2+) signaling mechanism present in most animal cells. SOCE refers to Ca(2+) influx that is activated by depletion of sarco/endoplasmic reticulum (S/ER) Ca(2+) stores. The main components of SOCE are STIM and Orai. STIM proteins function as S/ER Ca(2+) sensors, and upon S/ER Ca(2+) depletion STIM rearranges to S/ER-plasma membrane junctions and activates Orai Ca(2+) influx channels. Studies have implicated SOCE in cardiac hypertrophy pathogenesis, but SOCE's role in normal heart physiology remains poorly understood. This study analyzed heart-specific SOCE function in Drosophila, a powerful animal model of cardiac physiology. Heart-specific suppression of Stim and Orai in larvae and adults resulted in reduced contractility consistent with dilated cardiomyopathy. Myofibers were also highly disorganized in Stim and Orai RNAi hearts, reflecting possible decompensation or upregulated stress signaling. Furthermore, this study showed that reduced heart function due to SOCE suppression adversely affected animal viability, as heart specific Stim and Orai RNAi animals exhibited significant delays in post-embryonic development and adults died earlier than controls. Collectively, these results demonstrate that SOCE is essential for physiological heart function, and establish Drosophila as an important model for understanding the role of SOCE in cardiac pathophysiology.

Lepa, C. et al. (2020). LIM and SH3 protein 1 (LASP-1): A novel link between the slit membrane and actin cytoskeleton dynamics in podocytes. FASEB J. PubMed ID: 32086849
Summary:
The foot processes of podocytes exhibit a dynamic actin cytoskeleton, which maintains their complex cell structure and antagonizes the elastic forces of the glomerular capillary. Interdigitating secondary foot processes form a highly selective filter for proteins in the kidney, the slit membrane. Knockdown of slit membrane components such as Nephrin or Neph1 and cytoskeletal adaptor proteins such as CD2AP in mice leads to breakdown of the filtration barrier with foot process effacement, proteinuria, and early death of the mice. Less is known about the crosstalk between the slit membrane-associated proteins and cytoskeletal components inside the podocyte foot processes. This study shows that LASP-1, an actin-binding protein, is highly expressed in podocytes. Electron microscopy studies demonstrate that LASP-1 is found at the slit membrane suggesting a role in anchoring slit membrane components to the actin cytoskeleton. Live cell imaging experiments with transfected podocytes reveal that LASP-1 is either part of a highly dynamic granular complex or a static, actin cytoskeleton-bound protein. This study identified CD2AP as a novel LASP-1 binding partner that regulates its association with the actin cytoskeleton. Activation of the renin-angiotensin-aldosterone system, which is crucial for podocyte function, leads to phosphorylation and altered localization of LASP-1. In vivo studies using the Drosophila nephrocyte model indicate that Lasp is necessary for the slit membrane integrity and functional filtration.

Kang, D. and Douglas, A. E. (2020). Functional traits of the gut microbiome correlated with host lipid content in a natural population of Drosophila melanogaster. Biol Lett 16(2): 20190803. PubMed ID: 32097599
Summary:
Most research on the nutritional significance of the gut microbiome is conducted on laboratory animals, and its relevance to wild animals is largely unknown. This study investigated the microbiome correlates of lipid content in individual wild fruit flies, Drosophila melanogaster. Lipid content varied 3.6-fold among the flies and was significantly correlated with the abundance of gut-derived bacterial DNA sequences that were assigned to genes contributing to 16 KEGG pathways. These included genes encoding sugar transporters and enzymes in glycolysis/gluconeogenesis, potentially promoting sugar consumption by the gut microbiome and, thereby, a lean fly phenotype. Furthermore, the lipid content of wild flies was significantly lower than laboratory flies, indicating that, as for some mammalian models, certain laboratory protocols might be obesogenic for Drosophila. This study demonstrates the value of research on natural populations to identify candidate microbial genes that influence ecologically important host traits.

Nagai, H., Kurata, S. and Yano, T. (2020). Immunoglobulin superfamily beat-Ib mediates intestinal regeneration induced by reactive oxygen species in Drosophila. Genes Cells. PubMed ID: 32080940
Summary:
Reactive oxygen species (ROS) often injure intestinal epithelia that cause loss of damaged cells, which is mainly repaired by proliferation of intestinal stem cells (ISCs). To maintain the homeostatic state, coordination of sensing of the ROS injury and the subsequent epithelial cell loss with the replenishment by cell renewal is crucial. However, little is known about how gut epithelial cells initiate regenerative responses against ROS to maintain the tissue integrity. A genome-wide screen was carried out, by which immunoglobulin superfamily beaten path Ib (beat-Ib) as an essential gene for provoking ISC proliferation against ROS in Drosophila intestine. Interestingly, the beat-Ib function is required in differentiated enterocytes, the main targeted cells by ROS in the intestinal tract, but is dispensable in the stem cells. Moreover, beat-Ib is not involved in enterocyte apoptosis at ROS injury. These findings indicate the essential role of beat-Ib in Drosophila midgut enterocytes for initiating the non-cell-autonomous induction of ISC division in response to environmental ROS stresses.

McCracken, A. W., Adams, G., Hartshorne, L., Tatar, M. and Simons, M. J. P. (2020). The hidden costs of dietary restriction: Implications for its evolutionary and mechanistic origins. Sci Adv 6(8): eaay3047. PubMed ID: 32128403
Summary:
Dietary restriction (DR) extends life span across taxa. Despite considerable research, universal mechanisms of DR have not been identified, limiting its translational potential. Guided by the conviction that DR evolved as an adaptive, pro-longevity physiological response to food scarcity, biomedical science has interpreted DR as an activator of pro-longevity molecular pathways. Current evolutionary theory predicts that organisms invest in their soma during DR, and thus when resource availability improves, should outcompete rich-fed controls in survival and/or reproduction. Testing this prediction in Drosophila melanogaster (N > 66,000 across 11 genotypes), these experiments revealed substantial, unexpected mortality costs when flies returned to a rich diet following DR. The physiological effects of DR should therefore not be interpreted as intrinsically pro-longevity, acting via somatic maintenance. It is suggested that DR could alternatively be considered an escape from costs incurred under nutrient-rich conditions, in addition to costs associated with DR.

Lucke, J., Kaltofen, S., Hansson, B. S. and Wicher, D. (2020). The role of mitochondria in shaping odor responses in Drosophila melanogaster olfactory sensory neurons. Cell Calcium 87: 102179. PubMed ID: 32070926
Summary:
Insects detect volatile chemosignals with olfactory sensory neurons (OSNs) that express olfactory receptors. Among them, the most sensitive receptors are the odorant receptors (ORs), which form cation channels passing also Ca(2+). This study investigated if and how odor-induced Ca(2+) signals in Drosophila melanogaster OSNs are controlled by intracellular Ca(2+) stores, especially by mitochondria. Using an open antenna preparation that allows observation and pharmacological manipulation of OSNs Ca(2+) imaging was performed to determine the role of Ca(2+) influx and efflux pathways in OSN mitochondria. The results indicate that mitochondria participate in shaping the OR responses. The major players of this modulation are the mitochondrial calcium uniporter and the mitochondrial permeability transition pore. Intriguingly, OR-induced Ca(2+) signals were only mildly affected by modulating the Ca(2+) management of the endoplasmic reticulum (Lucke, 2020).

Friday, April 24th - Signaling

Malpe, M. S., McSwain, L. F., Kudyba, K., Ng, C. L., Nicholson, J., Brady, M., Qian, Y., Choksi, V., Hudson, A. G., Parrott, B. B. and Schulz, C. (2020). G-protein signaling is required for increasing germline stem cell division frequency in response to mating in Drosophila males. Sci Rep 10(1): 3888. PubMed ID: 32127590
Summary:
Adult stem cells divide to renew the stem cell pool and replenish specialized cells that are lost due to death or usage. However, little is known about the mechanisms regulating how stem cells adjust to a demand for specialized cells. A failure of the stem cells to respond to this demand can have serious consequences, such as tissue loss, or prolonged recovery post injury. This study challenged the male germline stem cells (GSCs) of Drosophila melanogaster for the production of specialized cells, sperm cells, using mating experiments. Repeated mating reduced the sperm pool and increased the percentage of GSCs in M- and S-phase of the cell cycle. The increase in dividing GSCs depended on the activity of the highly conserved G-proteins. Germline expression of RNA-Interference (RNA-i) constructs against G-proteins, or a dominant negative G-protein eliminated the increase in GSC division frequency in mated males. Consistent with a role for the G-proteins in regulating GSC division frequency, RNA-i against seven out of 35 G-protein coupled receptors (GPCRs) within the germline cells also eliminated the capability of males to increase the numbers of dividing GSCs in response to mating.

Ly, S., Lee, D. A., Strus, E., Prober, D. A. and Naidoo, N. (2020). Evolutionarily Conserved Regulation of Sleep by the Protein Translational Regulator PERK. Curr Biol. PubMed ID: 32169212
Summary:
Sleep is a cross-species phenomenon whose evolutionary and biological function remain poorly understood. Clinical and animal studies suggest that sleep disturbance is significantly associated with disruptions in protein homeostasis-or proteostasis-in the brain, but the mechanism of this link has not been explored. In the cell, the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) pathway modulates proteostasis by transiently inhibiting protein synthesis in response to proteostatic stress. This study examined the role of the PERK pathway in sleep regulation and provides the first evidence that PERK signaling is required to regulate normal sleep in both vertebrates and invertebrates. Pharmacological inhibition of PERK reduces sleep in both Drosophila and zebrafish, indicating an evolutionarily conserved requirement for PERK in sleep. Genetic knockdown of PERK activity also reduces sleep in Drosophila, whereas PERK overexpression induces sleep. Finally, changes in PERK signaling were demonstrated to directly impact wake-promoting neuropeptide expression, revealing a mechanism through which proteostatic pathways can affect sleep and wake behavior. Taken together, these results demonstrate that protein synthesis pathways like PERK could represent a general mechanism of sleep and wake regulation and provide greater insight into the relationship between sleep and proteostasis.

Matsumura, T., Uryu, O., Matsuhisa, F., Tajiri, K., Matsumoto, H. and Hayakawa, Y. (2020). N-acetyl-l-tyrosine is an intrinsic triggering factor of mitohormesis in stressed animals. EMBO Rep: e49211. PubMed ID: 32118349
Summary:
Under stress conditions, mitochondria release low levels of reactive oxygen species (ROS), which triggers a cytoprotective response, called "mitohormesis". It still remains unclear how mitochondria respond to stress-derived stimuli and release a low level of ROS. This study shows that N-acetyl-l-tyrosine (NAT) functions as a plausible intrinsic factor responsible for these tasks in stressed animals. NAT is present in the blood or hemolymph of healthy animals, and its concentrations increase in response to heat stress. Pretreatment with NAT significantly increases the stress tolerance of tested insects and mice. Analyses using Drosophila larvae and cultured cells demonstrate that the hormetic effects are triggered by transient NAT-induced perturbation of mitochondria, which causes a small increase in ROS production and leads to sequential retrograde responses: NAT-dependent FoxO activation increases in the gene expression of antioxidant enzymes and Keap1. Moreover, NAT represses tumor growth, possibly via the activation of Keap1. In sum, it is proposed that NAT is a vital endogenous molecule that could serve as a triggering factor for mitohormesis.

Neal, S. J., Zhou, Q. and Pignoni, F. (2020). STRIPAK-PP2A regulates Hippo-Yorkie signaling to suppress retinal fate in the Drosophila eye disc peripodial epithelium. J Cell Sci. PubMed ID: 32184260
Summary:
The specification of organs, tissues and cell types results from cell fate restrictions enacted by nuclear transcription factors under the control of conserved signaling pathways. The progenitor epithelium of the Drosophila compound eye, the eye imaginal disc, is a premier model for the study of such processes. Early in development, apposing cells of the eye disc are established as either retinal progenitors or support cells of the peripodial epithelium (PE), in a process whose genetic and mechanistic determinants are poorly understood. This study identified Protein Phosphatase 2A (PP2A), and specifically a STRIPAK-PP2A complex that includes the scaffolding and substrate-specificity components Cka, Strip and SLMAP, as a critical player in the retina-PE fate choice.These factors suppress ectopic retina formation in the presumptive PE and do so via the Hippo signaling axis. STRIPAK-PP2A negatively regulates Hpo kinase, and consequently its substrate Wts, to release the transcriptional co-activator Yki into the nucleus. Thus, a modular higher-order PP2A complex refines the activity of this general phosphatase to act in a precise specification of cell fate.

Nguyen, T. H., Ralbovska, A. and Kugler, J. M. (2020). RhoBTB Proteins Regulate the Hippo Pathway by Antagonizing Ubiquitination of LKB1. G3 (Bethesda). PubMed ID: 32111652
Summary:
The Hippo pathway regulates growth and apoptosis. This study identifirf RhoBTB proteins as novel regulators of Hippo signaling. RhoBTB depletion in the Drosophila wing disc epithelium cooperated with Yki to drive hyperplasia into neoplasia. Depletion of RhoBTB2 caused elevated YAP activity in human cells. RhoBTB2 deficiency resulted in increased colony formation in assays for anchorage-independent growth. Evidence that RhoBTBs acts on Hippo signaling through regulation of the kinase LKB1. LKB1 protein levels were reduced upon RhoBTB2 depletion which correlated with increased LKB1 ubiquitination. Restoring LKB1 levels rescued loss of RhoBTB in Drosophila. These results suggest that RhoBTB-dependent LKB1 regulation may contribute to its tumor-suppressive function.

Keenan, S. E., Blythe, S. A., Marmion, R. A., Djabrayan, N. J., Wieschaus, E. F. and Shvartsman, S. Y. (2020). Rapid dynamics of signal-dependent transcriptional repression by Capicua. Dev Cell. PubMed ID: 32142631
Summary:
Optogenetic perturbations, live imaging, and time-resolved ChIP-seq assays in Drosophila embryos were used to dissect the ERK-dependent control of the HMG-box repressor Capicua (Cic), which plays critical roles in development and is deregulated in human spinocerebellar ataxia and cancers. It was established that Cic target genes are activated before significant downregulation of nuclear localization of Cic, and their activation was demonstrated to be preceded by fast dissociation of Cic from the regulatory DNA. Both Cic-DNA binding and repression are rapidly reinstated in the absence of ERK activation, revealing that inductive signaling must be sufficiently sustained to ensure robust transcriptional response. This work provides a quantitative framework for the mechanistic analysis of dynamics and control of transcriptional repression in development.

Thursday, April 23rd - Adult Neural Development and Function

Li, H., Li, T., Horns, F., Li, J., Xie, Q., Xu, C., Wu, B., Kebschull, J. M., McLaughlin, C. N., Kolluru, S. S., Jones, R. C., Vacek, D., Xie, A., Luginbuhl, D. J., Quake, S. R. and Luo, L. (2020). Single-Cell Transcriptomes Reveal Diverse Regulatory Strategies for Olfactory Receptor Expression and Axon Targeting. Curr Biol. PubMed ID: 32059767
Summary:
The regulatory mechanisms by which neurons coordinate their physiology and connectivity are not well understood. The Drosophila olfactory receptor neurons (ORNs) provide an excellent system to investigate this question. Each ORN type expresses a unique olfactory receptor, or a combination thereof, and sends their axons to a stereotyped glomerulus. Using single-cell RNA sequencing, this study identified 33 transcriptomic clusters for ORNs, and 20 were mapped to their glomerular types, demonstrating that transcriptomic clusters correspond well with anatomically and physiologically defined ORN types. Each ORN type expresses hundreds of transcription factors. Transcriptome-instructed genetic analyses revealed that (1) one broadly expressed transcription factor (Acj6) only regulates olfactory receptor expression in one ORN type and only wiring specificity in another type, (2) one type-restricted transcription factor (Forkhead) only regulates receptor expression, and (3) another type-restricted transcription factor (Unplugged) regulates both events. Thus, ORNs utilize diverse strategies and complex regulatory networks to coordinate their physiology and connectivity.

Lai, Y. W., Chu, S. Y., Li, J. C., Chen, P. L., Chen, C. H. and Yu, H. H. (2020). Visualization of Endogenous Type I TGF-beta Receptor Baboon in the Drosophila Brain. Sci Rep 10(1): 5132. PubMed ID: 32198477
Summary:
The transforming growth factor beta (TGF-beta) signaling pathway is evolutionarily conserved and widely used in the animal kingdom to regulate diverse developmental processes. Prior studies have shown that Baboon (Babo), a Drosophila type I TGF-beta receptor, plays essential roles in brain development and neural circuit formation. However, the expression pattern for Babo in the developing brain has not been previously reported. This study generated a knock-in fly with a human influenza hemagglutinin (HA) tag at the C-terminus of Babo and assessed its localization. Babo::HA was primarily expressed in brain structures enriched with neurites, including the mushroom body lobe and neuropils of the optic lobe, where Babo has been shown to instruct neuronal morphogenesis. Since the babo 3' untranslated region contains a predicted microRNA-34 (miR-34) target sequence, tests were performed to see whether Babo::HA expression was affected by modulating the level of miR-34. Babo was found to be upregulated by mir-34 deletion and downregulated by miR-34 overexpression, confirming that it is indeed a miR-34 target gene. Taken together, these results demonstrate that the babo(HA) fly permits accurate visualization of endogenous Babo expression during brain development and the construction of functional neural circuits.

Hervas, R., Rau, M. J., Park, Y., Zhang, W., Murzin, A. G., Fitzpatrick, J. A. J., Scheres, S. H. W. and Si, K. (2020). Cryo-EM structure of a neuronal functional amyloid implicated in memory persistence in Drosophila. Science 367(6483): 1230-1234. PubMed ID: 32165583
Summary:
How long-lived memories withstand molecular turnover is a fundamental question. Aggregates of a prion-like RNA-binding protein, cytoplasmic polyadenylation element-binding (CPEB) protein, is a putative substrate of long-lasting memories. This study isolated aggregated Drosophila CPEB, Orb2, from adult heads and determined its activity and atomic structure, at 2.6-angstrom resolution, using cryo-electron microscopy. Orb2 formed ~75-nanometer-long threefold-symmetric amyloid filaments. Filament formation transformed Orb2 from a translation repressor to an activator and "seed" for further translationally active aggregation. The 31-amino acid protofilament core adopted a cross-beta unit with a single hydrophilic hairpin stabilized through interdigitated glutamine packing. Unlike the hydrophobic core of pathogenic amyloids, the hydrophilic core of Orb2 filaments suggests how some neuronal amyloids could be a stable yet regulatable substrate of memory.

Li, G., Forero, M. G., Wentzell, J. S., Durmus, I., Wolf, R., Anthoney, N. C., Parker, M., Jiang, R., Hasenauer, J., Strausfeld, N. J., Heisenberg, M. and Hidalgo, A. (2020). A Toll-receptor map underlies structural brain plasticity. Elife 9. PubMed ID: 32066523
Summary:
Experience alters brain structure, but the underlying mechanism remained unknown. Structural plasticity reveals that brain function is encoded in generative changes to cells that compete with destructive processes driving neurodegeneration. At an adult critical period, experience increases fiber number and brain size in Drosophila. This study asked if Toll receptors are involved. Tolls demarcate a map of brain anatomical domains. Focusing on Toll-2, loss of function caused apoptosis, neurite atrophy and impaired behaviour. Toll-2 gain of function and neuronal activity at the critical period increased cell number. Toll-2 induced cycling of adult progenitor cells via a novel pathway, that antagonized MyD88-dependent quiescence, and engaged Weckle and Yorkie downstream. Constant knock-down of multiple Tolls synergistically reduced brain size. Conditional over-expression of Toll-2 and wek at the adult critical period increased brain size. Through their topographic distribution, Toll receptors regulate neuronal number and brain size, modulating structural plasticity in the adult brain.

Linneweber, G. A., Andriatsilavo, M., Dutta, S. B., Bengochea, M., Hellbruegge, L., Liu, G., Ejsmont, R. K., Straw, A. D., Wernet, M., Hiesinger, P. R. and Hassan, B. A. (2020). A neurodevelopmental origin of behavioral individuality in the Drosophila visual system. Science 367(6482): 1112-1119. PubMed ID: 32139539
Summary:
The genome versus experience dichotomy has dominated understanding of behavioral individuality. By contrast, the role of nonheritable noise during brain development in behavioral variation is understudied. Using Drosophila melanogaster, this study demonstrated a link between stochastic variation in brain wiring and behavioral individuality. A visual system circuit called the dorsal cluster neurons (DCN; ~40 clustered neurons located in the dorso-lateral central brain) shows nonheritable, interindividual variation in right/left wiring asymmetry and controls object orientation in freely walking flies. DCN wiring asymmetry instructs an individual's object responses: The greater the asymmetry, the better the individual orients toward a visual object. Silencing DCNs abolishes correlations between anatomy and behavior, whereas inducing DCN asymmetry suffices to improve object responses.

Keles, M. F., Hardcastle, B. J., Stadele, C., Xiao, Q. and Frye, M. A. (2020). Inhibitory interactions and columnar inputs to an object motion detector in Drosophila. Cell Rep 30(7): 2115-2124. PubMed ID: 32075756
Summary:
The direction-selective T4/T5 cells innervate optic-flow processing projection neurons in the lobula plate of the fly that mediate the visual control of locomotion. In the lobula, visual projection neurons coordinate complex behavioral responses to visual features, however, the input circuitry and computations that bestow their feature-detecting properties are less clear. A highly specialized small object motion detector, LC11, was studied, and its responses were shown to be suppressed by local background motion. LC11 expresses GABA-A receptors that serve to sculpt responses to small objects but are not responsible for the rejection of background motion. Instead, LC11 is innervated by columnar T2 and T3 neurons that are themselves highly sensitive to small static or moving objects, insensitive to wide-field motion and, unlike T4/T5, respond to both ON and OFF luminance steps.