Recurrent Duplication and Diversification of a Vital DNA Repair Gene Family Across Drosophila.

Maintaining genome integrity is vital for organismal survival and reproduction. Essential, broadly conserved DNA repair pathways actively preserve genome integrity. However, many DNA repair proteins evolve adaptively. Ecological forces like UV exposure are classically cited drivers of DNA repair evolution. Intrinsic forces like repetitive DNA, which also imperil genome integrity, have received less attention. We recently reported that a Drosophila melanogaster-specific DNA satellite array triggered species-specific, adaptive evolution of a DNA repair protein called Spartan/MH. The Spartan family of proteases cleave hazardous, covalent crosslinks that form between DNA and proteins ("DNA-protein crosslink repair"). Appreciating that DNA satellites are both ubiquitous and universally fast-evolving, we hypothesized that satellite DNA turnover spurs adaptive evolution of DNA-protein crosslink repair beyond a single gene and beyond the D. melanogaster lineage. This hypothesis predicts pervasive Spartan gene family diversification across Drosophila species. To study the evolutionary history of the Drosophila Spartan gene family, we conducted population genetic, molecular evolution, phylogenomic, and tissue-specific expression analyses. We uncovered widespread signals of positive selection across multiple Spartan family genes and across multiple evolutionary timescales. We also detected recurrent Spartan family gene duplication, divergence, and gene loss. Finally, we found that ovary-enriched parent genes consistently birthed functionally diverged, testis-enriched daughter genes. To account for Spartan family diversification, we introduce a novel mechanistic model of antagonistic coevolution that links DNA satellite evolution and adaptive regulation of Spartan protease activity. This framework promises to accelerate our understanding of how DNA repeats drive recurrent evolutionary innovation to preserve genome integrity.

Re-assessment of the subcellular localization of Bazooka/Par-3 in Drosophila: no evidence for localization to the nucleus and the neuromuscular junction.

Bazooka/Par-3 (Baz) is an evolutionarily conserved scaffold protein that functions as a master regulator for the establishment and maintenance of cell polarity in many different cell types. In the vast majority of published research papers Baz has been reported to localize at the cell cortex and at intercellular junctions. However, there have also been several reports showing localization and function of Baz at additional subcellular sites, in particular the nuclear envelope and the neuromuscular junction. In this study we have re-assessed the localization of Baz to these subcellular sites in a systematic manner. We used antibodies raised in different host animals against different epitopes of Baz for confocal imaging of Drosophila tissues. We tested the specificity of these antisera by mosaic analysis with null mutant baz alleles and tissue-specific RNAi against baz. In addition, we used a GFP-tagged gene trap line for Baz and a bacterial artificial chromosome (BAC) expressing GFP-tagged Baz under control of its endogenous promoter in a baz mutant background to compare the subcellular localization of the GFP-Baz fusion proteins to the staining with anti-Baz antisera. Together, these experiments did not provide evidence for specific localization of Baz to the nucleus or the neuromuscular junction.

Variant functional assessment in Drosophila by overexpression: what can we learn?

The last decade has been highlighted by the increased use of next-generation DNA sequencing technology to identify novel human disease genes. A critical downstream part of this process is assigning function to a candidate gene variant. Functional studies in Drosophila melanogaster, the common fruit fly, have made a prominent contribution in annotating variant impact in an in vivo system. The use of patient-derived knock-in flies or rescue-based, "humanization", approaches are novel and valuable strategies in variant testing but have been recently widely reviewed. An often-overlooked strategy for determining variant impact has been GAL4/upstream activation sequence-mediated tissue-defined overexpression in Drosophila. This mini-review will summarize the recent contribution of ectopic overexpression of human reference and variant cDNA in Drosophila to assess variant function, interpret the consequence of the variant, and in some cases infer biological mechanisms.

The Drosophila tumor necrosis factor receptor, Wengen, couples energy expenditure with gut immunity.

It is well established that tumor necrosis factor (TNF) plays an instrumental role in orchestrating the metabolic disorders associated with late stages of cancers. However, it is not clear whether TNF/TNF receptor (TNFR) signaling controls energy homeostasis in healthy individuals. Here, we show that the highly conserved Drosophila TNFR, Wengen (Wgn), is required in the enterocytes (ECs) of the adult gut to restrict lipid catabolism, suppress immune activity, and maintain tissue homeostasis. Wgn limits autophagy-dependent lipolysis by restricting cytoplasmic levels of the TNFR effector, TNFR-associated factor 3 (dTRAF3), while it suppresses immune processes through inhibition of the dTAK1/TAK1-Relish/NF-κB pathway in a dTRAF2-dependent manner. Knocking down dTRAF3 or overexpressing dTRAF2 is sufficient to suppress infection-induced lipid depletion and immune activation, respectively, showing that Wgn/TNFR functions as an intersection between metabolism and immunity allowing pathogen-induced metabolic reprogramming to fuel the energetically costly task of combatting an infection.

A conserved domain of Drosophila RNA-binding protein Pumilio interacts with multiple CCR4-NOT deadenylase complex subunits to repress target mRNAs.

Pumilio is a sequence-specific RNA-binding protein that controls development, stem cell fate, and neurological functions in Drosophila. Pumilio represses protein expression by destabilizing target mRNAs in a manner dependent on the CCR4-NOT deadenylase complex. Three unique repression domains in the N-terminal region of Pumilio were previously shown to recruit CCR4-NOT, but how they do so was not well understood. In this study, we identified the motifs that are necessary and sufficient for the activity of the third repression domain of Pumilio, designated RD3, which is present in all isoforms and has conserved regulatory function. We identified multiple conserved regions of RD3 that are important for repression activity in cell-based reporter gene assays. Using yeast two-hybrid assays, we show that RD3 contacts specific regions of the Not1, Not2, and Not3 subunits of the CCR4-NOT complex. Our results indicate that RD3 makes multivalent interactions with CCR4-NOT mediated by conserved short linear interaction motifs. Specifically, two phenylalanine residues in RD3 make crucial contacts with Not1 that are essential for its repression activity. Using reporter gene assays, we also identify three new target mRNAs that are repressed by Pumilio and show that RD3 contributes to their regulation. Together, these results provide important insights into the mechanism by which Pumilio recruits CCR4-NOT to regulate the expression of target mRNAs.

The rate of thermodynamic cost against adiabatic and nonadiabatic fluctuations of a single gene circuit in Drosophila embryos.

We study the stochastic dynamics of the externally regulating gene circuit as an example of an eve-skipped gene stripe in the development of Drosophila. Three gene regulation regimes are considered: an adiabatic phase when the switching rate of the gene from the OFF to ON state is faster than the rate of mRNA degradation; a nonadiabatic phase when the switching rate from the OFF to ON state is slower than that of the mRNA degradation; and a bursting phase when the gene switching is fast and transcription is very fast, while the ON state probability is very low. We found that the rate of thermodynamic cost quantified by the entropy production rate can suppress the fluctuations of the gene circuit. A higher (lower) rate of thermodynamic cost leads to reduced (increased) fluctuations in the number of gene products in the adiabatic (nonadiabatic) regime. We also found that higher thermodynamic cost is often required to sustain the emergence of more gene states and, therefore, more heterogeneity coming from genetic mutations or epigenetics. We also study the stability of the gene state using the mean first passage time from one state to another. We found the monotonic decrease in time, i.e., in the stability of the state, in the transition from the nonadiabatic to adiabatic regimes. Therefore, as the higher rate of thermodynamic cost suppresses the fluctuations, higher stability requires higher thermodynamics cost to maintain.

An assessment of the rescue action of resveratrol in parkin loss of function-induced oxidative stress in Drosophila melanogaster.

Loss-of-function mutations in parkin is associated with onset of juvenile Parkinson's disease (PD). Resveratrol is a polyphenolic stilbene with neuroprotective activity. Here, we evaluated the rescue action of resveratrol in parkin mutant D. melanogaster. The control flies (w1118) received diet-containing 2% ethanol (vehicle), while the PD flies received diets-containing resveratrol (15, 30 and 60 mg/kg diet) for 21 days to assess survival rate. Consequently, similar treatments were carried out for 10 days to evaluate locomotor activity, oxidative stress and antioxidant markers. We also determined mRNA levels of Superoxide dismutase 1 (Sod1, an antioxidant gene) and ple, which encodes tyrosine hydroxylase, the rate-limiting step in dopamine synthesis. Our data showed that resveratrol improved survival rate and climbing activity of PD flies compared to untreated PD flies. Additionally, resveratrol protected against decreased activities of acetylcholinesterase and catalase and levels of non-protein thiols and total thiols displayed by PD flies. Moreover, resveratrol mitigated against parkin mutant-induced accumulations of hydrogen peroxide, nitric oxide and malondialdehyde. Resveratrol attenuated downregulation of ple and Sod1 and reduction in mitochondrial fluorescence intensity displayed by PD flies. Overall, resveratrol alleviated oxidative stress and locomotor deficit associated with parkin loss-of-function mutation and therefore might be useful for the management of PD.

A phylogenetic analysis between humans and D. melanogaster: A repertoire of solute carriers in humans and flies.

The solute carrier (SLC) superfamily is the largest group of transporters in humans, with the role to transport solutes across plasma membranes. The SLCs are currently divided into 65 families with 430 members. Here, we performed a detailed mining of the SLC superfamily and the recent annotated family of "atypical" SLCs in human and D. melanogaster using Hidden Markov Models and PSI-BLAST. Our analyses identified 381 protein sequences in D. melanogaster and of those, 55 proteins have not been previously identified in flies. In total, 11 of the 65 human SLC families were found to not be conserved in flies, while a few families are highly conserved, which perhaps reflects the families' functions and roles in cellular pathways. This study provides the first collection of all SLC sequences in D. melanogaster and can serve as a SLC database to be used for classification of SLCs in other phyla.

Modulating the bicoid gradient in space and time.

BACKGROUND: The formation of the Bicoid (Bcd) gradient in the early Drosophila is one of the most fascinating observations in biology and serves as a paradigm for gradient formation, yet its mechanism is still not fully understood. Two distinct models were proposed in the past, the SDD and the ARTS model. RESULTS: We define novel cis- and trans-acting factors that are indispensable for gradient formation. The first one is the poly A tail length of the bcd mRNA where we demonstrate that it changes not only in time, but also in space. We show that posterior bcd mRNAs possess a longer poly tail than anterior ones and this elongation is likely mediated by wispy (wisp), a poly A polymerase. Consequently, modulating the activity of Wisp results in changes of the Bcd gradient, in controlling downstream targets such as the gap and pair-rule genes, and also in influencing the cuticular pattern. Attempts to modulate the Bcd gradient by subjecting the egg to an extra nuclear cycle, i.e. a 15th nuclear cycle by means of the maternal haploid (mh) mutation showed no effect, neither on the appearance of the gradient nor on the control of downstream target. This suggests that the segmental anlagen are determined during the first 14 nuclear cycles. Finally, we identify the Cyclin B (CycB) gene as a trans-acting factor that modulates the movement of Bcd such that Bcd movement is allowed to move through the interior of the egg. CONCLUSIONS: Our analysis demonstrates that Bcd gradient formation is far more complex than previously thought requiring a revision of the models of how the gradient is formed.

Cost-precision trade-off relation determines the optimal morphogen gradient for accurate biological pattern formation.

Spatial boundaries formed during animal development originate from the pre-patterning of tissues by signaling molecules, called morphogens. The accuracy of boundary location is limited by the fluctuations of morphogen concentration that thresholds the expression level of target gene. Producing more morphogen molecules, which gives rise to smaller relative fluctuations, would better serve to shape more precise target boundaries; however, it incurs more thermodynamic cost. In the classical diffusion-depletion model of morphogen profile formation, the morphogen molecules synthesized from a local source display an exponentially decaying concentration profile with a characteristic length λ. Our theory suggests that in order to attain a precise profile with the minimal cost, λ should be roughly half the distance to the target boundary position from the source. Remarkably, we find that the profiles of morphogens that pattern the Drosophila embryo and wing imaginal disk are formed with nearly optimal λ. Our finding underscores the cost-effectiveness of precise morphogen profile formation in Drosophila development.

Functional assessment of the "two-hit" model for neurodevelopmental defects in Drosophila and X. laevis.

We previously identified a deletion on chromosome 16p12.1 that is mostly inherited and associated with multiple neurodevelopmental outcomes, where severely affected probands carried an excess of rare pathogenic variants compared to mildly affected carrier parents. We hypothesized that the 16p12.1 deletion sensitizes the genome for disease, while "second-hits" in the genetic background modulate the phenotypic trajectory. To test this model, we examined how neurodevelopmental defects conferred by knockdown of individual 16p12.1 homologs are modulated by simultaneous knockdown of homologs of "second-hit" genes in Drosophila melanogaster and Xenopus laevis. We observed that knockdown of 16p12.1 homologs affect multiple phenotypic domains, leading to delayed developmental timing, seizure susceptibility, brain alterations, abnormal dendrite and axonal morphology, and cellular proliferation defects. Compared to genes within the 16p11.2 deletion, which has higher de novo occurrence, 16p12.1 homologs were less likely to interact with each other in Drosophila models or a human brain-specific interaction network, suggesting that interactions with "second-hit" genes may confer higher impact towards neurodevelopmental phenotypes. Assessment of 212 pairwise interactions in Drosophila between 16p12.1 homologs and 76 homologs of patient-specific "second-hit" genes (such as ARID1B and CACNA1A), genes within neurodevelopmental pathways (such as PTEN and UBE3A), and transcriptomic targets (such as DSCAM and TRRAP) identified genetic interactions in 63% of the tested pairs. In 11 out of 15 families, patient-specific "second-hits" enhanced or suppressed the phenotypic effects of one or many 16p12.1 homologs in 32/96 pairwise combinations tested. In fact, homologs of SETD5 synergistically interacted with homologs of MOSMO in both Drosophila and X. laevis, leading to modified cellular and brain phenotypes, as well as axon outgrowth defects that were not observed with knockdown of either individual homolog. Our results suggest that several 16p12.1 genes sensitize the genome towards neurodevelopmental defects, and complex interactions with "second-hit" genes determine the ultimate phenotypic manifestation.

A putative novel role for Eip74EF in male reproduction in promoting sperm elongation at the cost of male fecundity.

Spermatozoa are the most morphologically variable cell type, yet little is known about genes controlling natural variation in sperm shape. Drosophila fruit flies have the longest sperm known, which are evolving under postcopulatory sexual selection, driven by sperm competition and cryptic female choice. Long sperm outcompete short sperm but primarily when females have a long seminal receptacle (SR), the primary sperm storage organ. Thus, the selection on sperm length is mediated by SR length, and the two traits are coevolving across the Drosophila lineage, driven by a genetic correlation and fitness advantage of long sperm and long SR genotypes in both males and females. Ecdysone-induced protein 74EF (Eip74EF) is expressed during postmeiotic stages of spermatogenesis when spermatid elongation occurs, and we found that it is rapidly evolving under positive selection in Drosophila. Hypomorphic knockout of the E74A isoform leads to shorter sperm but does not affect SR length, suggesting that E74A may be involved in promoting spermatid elongation but is not a genetic driver of male-female coevolution. We also found that E74A knockout has opposing effects on fecundity in males and females, with an increase in fecundity for males but a decrease in females, consistent with its documented role in oocyte maturation. Our results suggest a novel function of Eip74EF in spermatogenesis and demonstrates that this gene influences both male and female reproductive success. We speculate on possible roles for E74A in spermatogenesis and male reproductive success.

Hydroxylated sphingolipid biosynthesis regulates photoreceptor apical domain morphogenesis.

Apical domains of epithelial cells often undergo dramatic changes during morphogenesis to form specialized structures, such as microvilli. Here, we addressed the role of lipids during morphogenesis of the rhabdomere, the microvilli-based photosensitive organelle of Drosophila photoreceptor cells. Shotgun lipidomics analysis performed on mutant alleles of the polarity regulator crumbs, exhibiting varying rhabdomeric growth defects, revealed a correlation between increased abundance of hydroxylated sphingolipids and abnormal rhabdomeric growth. This could be attributed to an up-regulation of fatty acid hydroxylase transcription. Indeed, direct genetic perturbation of the hydroxylated sphingolipid metabolism modulated rhabdomere growth in a crumbs mutant background. One of the pathways targeted by sphingolipid metabolism turned out to be the secretory route of newly synthesized Rhodopsin, a major rhabdomeric protein. In particular, altered biosynthesis of hydroxylated sphingolipids impaired apical trafficking via Rab11, and thus apical membrane growth. The intersection of lipid metabolic pathways with apical domain growth provides a new facet to our understanding of apical growth during morphogenesis.

Isoform-specific functions of an evolutionarily conserved 3 bp micro-exon alternatively spliced from another exon in Drosophila homothorax gene.

Micro-exons are exons of very small size (usually 3-30 nts). Some micro-exons are alternatively spliced. Their functions, regulation and evolution are largely unknown. Here, we present an example of an alternatively spliced 3 bp micro-exon (micro-Ex8) in the homothorax (hth) gene in Drosophila. Hth is involved in many developmental processes. It contains a MH domain and a TALE-class homeodomain (HD). It binds to another homeodomain Exd via its MH domain to promote the nuclear import of the Hth-Exd complex and serve as a cofactor for Hox proteins. The MH and HD domains in Hth as well as the HTh-Exd interaction are highly conserved in evolution. The alternatively spliced micro-exon lies between the exons encoding the MH and HD domains. We provide clear proof that the micro-Ex8 is produced by alternative splicing from a 48 bp full-length exon 8 (FL-Ex8) and the micro-Ex8 is the first three nt is FL-Ex8. We found that the micro-Ex8 is the ancient form and the 3 + 48 organization of alternatively spliced overlapping exons only emerged in the Schizophora group of Diptera and is absolutely conserved in this group. We then used several strategies to test the in vivo function of the two types of isoforms and found that the micro-Ex8 and FL-Ex8 isoforms have largely overlapping functions but also have non-redundant functions that are tissue-specific, which supports their strong evolutionary conservation. Since the different combinations of protein interaction of Hth with Exd and/or Hox can have different DNA target specificity, our finding of alternatively spliced isoforms adds to the spectrum of structural and functional diversity under developmental regulation.

Evolutionary trade-offs of insecticide resistance - The fitness costs associated with target-site mutations in the nAChR of Drosophila melanogaster.

The evolution of resistance to drugs and pesticides poses a major threat to human health and food security. Neonicotinoids are highly effective insecticides used to control agricultural pests. They target the insect nicotinic acetylcholine receptor and mutations of the receptor that confer resistance have been slow to develop, with only one field-evolved mutation being reported to date. This is an arginine-to-threonine substitution at position 81 of the nAChR_ß1 subunit in neonicotinoid-resistant aphids. To validate the role of R81T in neonicotinoid resistance and to test whether it may confer any significant fitness costs to insects, CRISPR/Cas9 was used to introduce an analogous mutation in the genome of Drosophila melanogaster. Flies carrying R81T showed an increased tolerance (resistance) to neonicotinoid insecticides, accompanied by a significant reduction in fitness. In comparison, flies carrying a deletion of the whole nAChR_α6 subunit, the target site of spinosyns, showed an increased tolerance to this class of insecticides but presented almost no fitness deficits.

Bayesian model selection for the Drosophila gap gene network.

BACKGROUND: The gap gene system controls the early cascade of the segmentation pathway in Drosophila melanogaster as well as other insects. Owing to its tractability and key role in embryo patterning, this system has been the focus for both computational modelers and experimentalists. The gap gene expression dynamics can be considered strictly as a one-dimensional process and modeled as a system of reaction-diffusion equations. While substantial progress has been made in modeling this phenomenon, there still remains a deficit of approaches to evaluate competing hypotheses. Most of the model development has happened in isolation and there has been little attempt to compare candidate models. RESULTS: The Bayesian framework offers a means of doing formal model evaluation. Here, we demonstrate how this framework can be used to compare different models of gene expression. We focus on the Papatsenko-Levine formalism, which exploits a fractional occupancy based approach to incorporate activation of the gap genes by the maternal genes and cross-regulation by the gap genes themselves. The Bayesian approach provides insight about relationship between system parameters. In the regulatory pathway of segmentation, the parameters for number of binding sites and binding affinity have a negative correlation. The model selection analysis supports a stronger binding affinity for Bicoid compared to other regulatory edges, as shown by a larger posterior mean. The procedure doesn't show support for activation of Kruppel by Bicoid. CONCLUSIONS: We provide an efficient solver for the general representation of the Papatsenko-Levine model. We also demonstrate the utility of Bayes factor for evaluating candidate models for spatial pattering models. In addition, by using the parallel tempering sampler, the convergence of Markov chains can be remarkably improved and robust estimates of Bayes factors obtained.

Assessment of mitophagy in mt-Keima Drosophila revealed an essential role of the PINK1-Parkin pathway in mitophagy induction in vivo.

Mitophagy has been implicated in mitochondrial quality control and in various human diseases. However, the study of in vivo mitophagy remains limited. We previously explored in vivo mitophagy using a transgenic mouse expressing the mitochondria-targeted fluorescent protein Keima (mt-Keima). Here, we generated mt-Keima Drosophila to extend our efforts to study mitophagy in vivo. A series of experiments confirmed that mitophagy can be faithfully and quantitatively measured in mt-Keima Drosophila. We also showed that alterations in mitophagy upon environmental and genetic perturbation can be measured in mt-Keima Drosophila. Analysis of different tissues revealed a variation in basal mitophagy levels in Drosophila tissues. In addition, we found a significant increase in mitophagy levels during Drosophila embryogenesis. Importantly, loss-of-function genetic analysis demonstrated that the phosphatase and tensin homolog-induced putative kinase 1 (PINK1)-Parkin pathway is essential for the induction of mitophagy in vivo in response to hypoxic exposure and rotenone treatment. These studies showed that the mt-Keima Drosophila system is a useful tool for understanding the role and molecular mechanism of mitophagy in vivo. In addition, we demonstrated the essential role of the PINK1-Parkin pathway in mitophagy induction in response to mitochondrial dysfunction.-Kim, Y. Y., Um, J.-H., Yoon, J.-H., Kim, H., Lee, D.-Y., Lee, Y. J., Jee, H. J., Kim, Y. M., Jang, J. S., Jang, Y.-G., Chung, J., Park, H. T., Finkel, T., Koh, H., Yun, J. Assessment of mitophagy in mt-Keima Drosophila revealed an essential role of the PINK1-Parkin pathway in mitophagy induction in vivo.

Removal of extra sequences with I-SceI in combination with CRISPR/Cas9 technique for precise gene editing in Drosophila.

The CRISPR/Cas9 system has recently emerged as a powerful tool for functional genomic studies and has been adopted for many organisms, including Drosophila. Previously, an efficient two-step strategy was developed to engineer the fly genome by combining CRISPR/Cas9 with recombinase-mediated cassette exchange (RMCE). This strategy allows the introduction of designed mutations into a gene of interest in vivo. However, the loxP or frt site remains in the edited locus. Here, we propose a modification of this approach for rapid and efficient seamless genome editing with CRISPR/Cas9 and site-specific recombinase-mediated integration (SSRMI) combined with recombination between homologous sequences induced by the rare-cutting endonuclease I-SceI. The induced homological recombination leads to the removal of the remaining extraneous sequences from the target locus.

Neuroprotective effects of PACAP against paraquat-induced oxidative stress in the Drosophila central nervous system.

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder that can arise after long-term exposure to environmental oxidative stressors, such as the herbicide paraquat (PQ). Here we investigated the potential neuroprotective action of vertebrate pituitary adenylate cyclase-activating polypeptide (PACAP) against PQ in Drosophila. We found that pre-treatment with this neuropeptide applied to the ventral nerve cord (VNC) at low doses markedly extended the survival of wild-type decapitated flies exposed to neurotoxic levels of PQ or dopamine (DA). In contrast and interestingly, application of a PACAP receptor antagonist, PACAP-6-38, had opposite effects, significantly decreasing the resistance of flies to PQ. PACAP also reduced PQ-induced caspase activation and reactive oxygen species (ROS) accumulation in the VNC. We then searched for the endogenous neuropeptide receptor potentially involved in PACAP-mediated neuroprotection in Drosophila. Knocking down the gene encoding the receptor Han/PDFR of the neuropeptide pigment-dispersing factor (PDF) in all neurons conferred to flies higher resistance to PQ, whereas PDFR downregulation restricted to PDF or DA neurons did not increase PQ resistance, but remarkably suppressed the neuroprotective action of PACAP. Further experiments performed with Pdf and Pdfr-deficient mutant strains confirmed that PDF and its receptor are required for PACAP-mediated neuroprotection in flies. We also provide evidence using split-green fluorescent protein (split-GFP) reconstitution that PDF neurons make synaptic contacts onto DA neurons in the abdominal VNC. Our results therefore suggest that the protective action of PACAP against PQ-induced defects in the Drosophila nervous system involves the modulation of PDFR signaling in a small number of interconnected neurons.

Centriole planar polarity assessment in Drosophila wings.

In vertebrates, planar polarization of ciliary basal bodies has been associated with actin polymerization that occurs downstream of the Frizzled-planar cell polarity (Fz-PCP) pathway. In Drosophila wing epithelial cells, which do not have cilia, centrioles also polarize in a Fz-PCP-dependent manner, although the relationship with actin polymerization remains unknown. By combining existing and new quantitative methods, we unexpectedly found that known PCP effectors linked to actin polymerization phenotypes affect neither final centriole polarization nor apical centriole distribution. But actin polymerization is required upstream of Fz-PCP to maintain the centrioles in restricted areas in the apical-most planes of those epithelial cells before and after the actin-based hair is formed. Furthermore, in the absence of proper core Fz-PCP signalling, actin polymerization is insufficient to drive this off-centred centriole migration. Altogether, the results reveal that there are at least two pathways controlling centriole positioning in Drosophila pupal wings - an upstream actin-dependent mechanism involved in centriole distribution that is PCP independent, and an unknown mechanism that links core Fz-PCP and centriole polarization.