Clonal analysis of cmp44E, which encodes a conserved putative transmembrane protein, indicates a requirement for cell viability in Drosophila

Correlation between desiccation stress response and epigenetic modifications of genes in Drosophila melanogaster: An example of environment-epigenome interaction

Animals from different phyla including arthropods tolerate water stress to different extent. This tolerance is accompanied by biochemical changes which in turn are due to transcriptional alteration. The changes in transcription can be an indirect effect on some of the genes, ensuing from the effect of stress on the regulators of transcription including epigenetic regulators. Within this paradigm, we investigated the correlation between stress response and epigenetic modification underlying gene expression modulation during desiccation stress in Canton-S. We report altered resistance of flies in desiccation stress for heterozygote mutants of PcG and TrxG members. Pc/+ mutant shows lower survival, while ash1/+ mutants show higher survival under desiccation stress as compared to Canton-S. We detect expression alteration in stress related genes as well the genes of the Polycomb and trithorax complex in Canton-S subjected to desiccation stress. Concomitant with this, there is an altered enrichment of H3K27me3 and H3K4me3 at the upstream regions of the stress responsive genes. The enrichment of activating mark, H3K4me3, is higher in non-stress condition. H3K27me3, the repressive mark, is more pronounced under stress condition, which in turn, can be correlated with the binding of Pc. Our results show that desiccation stress induces dynamic switching in expression and enrichment of PcG and TrxG in the upstream region of genes, which correlates with histone modifications. We provide evidence that epigenetic modulation could be one of the mechanisms to adapt to the desiccation stress in Drosophila. Thus, our study proposes the interaction of epigenome and environmental factors.

Downregulation of RBO-PI4KIIIα Facilitates Aβ42 Secretion and Ameliorates Neural Deficits in Aβ42-Expressing Drosophila

Phosphoinositides and their metabolizing enzymes are involved in Aβ₄₂ metabolism and Alzheimer's disease pathogenesis. In yeast and mammals, Eighty-five requiring 3 (EFR3), whose Drosophila homolog is Rolling Blackout (RBO), forms a plasma membrane-localized protein complex with phosphatidylinositol-4-kinase Type IIIα (PI4KIIIα) and a scaffold protein to tightly control the level of plasmalemmal phosphatidylinositol-4-phosphate (PI₄P). Here, we report that RBO binds to Drosophila PI4KIIIα, and that in an Aβ₄₂-expressing Drosophila model, separate genetic reduction of PI4KIIIα and RBO, or pharmacological inhibition of PI4KIIIα ameliorated synaptic transmission deficit, climbing ability decline, premature death, and reduced neuronal accumulation of Aβ₄₂ Moreover, we found that RBO-PI4KIIIa downregulation increased neuronal Aβ₄₂ release and that PI4P facilitated the assembly or oligomerization of Aβ₄₂ in/on liposomes. These results indicate that RBO-PI4KIIIa downregulation facilitates neuronal Aβ₄₂ release and consequently reduces neuronal Aβ₄₂ accumulation likely via decreasing Aβ₄₂ assembly in/on plasma membrane. This study suggests the RBO-PI4KIIIα complex as a potential therapeutic target and PI4KIIIα inhibitors as drug candidates for Alzheimer's disease treatment.SIGNIFICANCE STATEMENT Phosphoinositides and their metabolizing enzymes are involved in Aβ₄₂ metabolism and Alzheimer's disease pathogenesis. Here, in an Aβ₄₂-expressing Drosophila model, we discovered and studied the beneficial role of downregulating RBO or its interacting protein PI4KIIIα-a protein that tightly controls the plasmalemmal level of PI₄P-against the defects caused by Aβ₄₂ expression. Mechanistically, RBO-PI4KIIIα downregulation reduced neuronal Aβ₄₂ accumulation, and interestingly increased neuronal Aβ₄₂ release. This study suggests the RBO-PI4KIIIα complex as a novel therapeutic target, and PI4KIIIα inhibitors as new drug candidates.

Brain-specific ablation of Efr3a promotes adult hippocampal neurogenesis via the brain-derived neurotrophic factor pathway

Efr3 is a newly identified plasma membrane protein and plays an important role in the phosphoinositide metabolism on the plasma membrane. However, although it is highly expressed in the brain, the functional significance of Efr3 in the brain is not clear. In the present study, we generated Efr3a^f/f mice and then crossed them with Nestin-Cre mice to delete Efr3a, one of the Efr3 isoforms, specifically in the brain. We found that brain-specific ablation of Efr3a promoted adult hippocampal neurogenesis by increasing survival and maturation of newborn neurons without affecting their dendritic tree morphology. Moreover, the brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) signaling pathway was significantly enhanced in the hippocampus of Efr3a-deficient mice, as reflected by increased expression of BDNF, TrkB, and the downstream molecules, including phospho-MAPK and phospho-Akt. Furthermore, the number of TUNEL⁺ cells was decreased in the subgranular zone of dentate gyrus in Efr3a-deficient mice compared with that of control mice. Our data suggest that brain-specific deletion of Efr3a could promote adult hippocampal neurogenesis, presumably by upregulating the expression of BDNF and its receptor, TrkB, and therefore provide new insight into the roles of Efr3 in the brain.-Qian, Q., Liu, Q., Zhou, D., Pan, H., Liu, Z., He, F., Ji, S., Wang, D., Bao, W., Liu, X., Liu, Z., Zhang, H., Zhang, X., Zhang, L., Wang, M., Xu, Y., Huang, F., Luo, B., Sun B. Brain-specific ablation of Efr3a promotes adult hippocampal neurogenesis via the brain-derived neurotrophic factor pathway.

Drosophila rolling blackout displays lipase domain-dependent and -independent endocytic functions downstream of dynamin

Drosophila temperature-sensitive rolling blackout (rbo(ts) ) mutants display a total block of endocytosis in non-neuronal cells and a weaker, partial defect at neuronal synapses. RBO is an integral plasma membrane protein and is predicted to be a serine esterase. To determine if lipase activity is required for RBO function, we mutated the catalytic serine 358 to alanine in the G-X-S-X-G active site, and assayed genomic rescue of rbo mutant non-neuronal and neuronal phenotypes. The rbo(S358A) mutant is unable to rescue rbo null 100% embryonic lethality, indicating that the lipase domain is critical for RBO essential function. Likewise, the rbo(S358A) mutant cannot provide any rescue of endocytic blockade in rbo(ts) Garland cells, showing that the lipase domain is indispensable for non-neuronal endocytosis. In contrast, rbo(ts) conditional paralysis, synaptic transmission block and synapse endocytic defects are all fully rescued by the rbo(S358A) mutant, showing that the RBO lipase domain is dispensable in neuronal contexts. We identified a synthetic lethal interaction between rbo(ts) and the well-characterized dynamin GTPase conditional shibire (shi(ts1)) mutant. In both non-neuronal cells and neuronal synapses, shi(ts1); rbo(ts) phenocopies shi(ts1) endocytic defects, indicating that dynamin and RBO act in the same pathway, with dynamin functioning upstream of RBO. We conclude that RBO possesses both lipase domain-dependent and scaffolding functions with differential requirements in non-neuronal versus neuronal endocytosis mechanisms downstream of dynamin GTPase activity.

Assembly of the PtdIns 4-kinase Stt4 complex at the plasma membrane requires Ypp1 and Efr3

The phosphoinositide phosphatidylinositol 4-phosphate (PtdIns4P) is an essential signaling lipid that regulates secretion and polarization of the actin cytoskeleton. In Saccharomyces cerevisiae, the PtdIns 4-kinase Stt4 catalyzes the synthesis of PtdIns4P at the plasma membrane (PM). In this paper, we identify and characterize two novel regulatory components of the Stt4 kinase complex, Ypp1 and Efr3. The essential gene YPP1 encodes a conserved protein that colocalizes with Stt4 at cortical punctate structures and regulates the stability of this lipid kinase. Accordingly, Ypp1 interacts with distinct regions on Stt4 that are necessary for the assembly and recruitment of multiple copies of the kinase into phosphoinositide kinase (PIK) patches. We identify the membrane protein Efr3 as an additional component of Stt4 PIK patches. Efr3 is essential for assembly of both Ypp1 and Stt4 at PIK patches. We conclude that Ypp1 and Efr3 are required for the formation and architecture of Stt4 PIK patches and ultimately PM-based PtdIns4P signaling.

Temperature-sensitive paralytic mutants: insights into the synaptic vesicle cycle

Forward genetic screens have identified numerous proteins with critical roles in neurotransmission. One particularly fruitful screening target in Drosophila has been TS (temperature-sensitive) paralytic mutants, which have revealed proteins acutely required in neuronal signalling. In the present paper, we review recent insights and current questions from one recently cloned TS paralytic mutant, rbo (rolling blackout). The rbo mutant identifies a putative integral lipase of the pre-synaptic plasma membrane that is required for the SV (synaptic vesicle) cycle. Identification of this mutant adds to a growing body of evidence that lipid-modifying enzymes locally control specialized lipid microenvironments and lipid signalling pathways with key functions regulating neurotransmission strength. The RBO protein is absolutely required for phospholipase C signalling in phototransduction. We posit that RBO might be required to regulate the availability of fusogenic lipids such as phosphatidylinositol 4,5-bisphosphate and diacylglycerol that may directly modify membrane properties and/or activate lipid-binding fusogenic proteins mediating SV exocytosis.

Rolling blackout, a newly identified PIP2-DAG pathway lipase required for Drosophila phototransduction

The rolling blackout (rbo) gene encodes an integral plasma membrane lipase required for Drosophila phototransduction. Photoreceptors are enriched for the RBO protein, and temperature-sensitive rbo mutants show reversible elimination of phototransduction within minutes, demonstrating an acute requirement for the protein. The block is activity dependent, indicating that the action of RBO is use dependent. Conditional rbo mutants show activity-dependent depletion of diacylglycerol and concomitant accumulation of phosphatidylinositol phosphate and phosphatidylinositol 4,5-bisphosphate within minutes of induction, suggesting rapid downregulation of phospholipase C (PLC) activity. The RBO requirement identifies an essential regulatory step in G-protein-coupled, PLC-dependent inositol lipid signaling mediating activation of TRP and TRPL channels during phototransduction.

Mouse homolog of KIAA0143 protein: hearing deficit induces specific changes of expression in auditory brainstem neurons

Hearing deficit induced by mechanical cochlear damage, intense noise or ototoxic drugs produces a variety of structural and functional changes in the inner ear and the auditory brainstem. In the present study, we identified a novel gene that has activity dependent plasticity in the superior olivary complex by using suppression subtractive hybridization. We cloned a gene that encodes mouse homolog of KIAA0143 protein, one derived from a series of unidentified human genes. This gene termed mKIAA0143 shows differential expression of mRNA in the lateral superior olive between mice with hearing deficit and those with normal hearing ability. The mRNA thus obtained encodes a unique membrane-bound protein that consists of 819 amino acids. The gene locus was mapped using genomic DNA databases to the mouse chromosome 15D1. Green fluorescent protein-tagged mKIAA0143 was expressed in COS-1 cells. It was amply seen in the cellular plasma membrane.

Drosophila lacking dfmr1 activity show defects in circadian output and fail to maintain courtship interest

Fragile X mental retardation is a prominent genetic disorder caused by the lack of the FMR1 gene product, a known RNA binding protein. Specific physiologic pathways regulated by FMR1 function have yet to be identified. Adult dfmr1 (also called dfxr) mutant flies display arrhythmic circadian activity and have erratic patterns of locomotor activity, whereas overexpression of dFMR1 leads to a lengthened period. dfmr1 mutant males also display reduced courtship activity which appears to result from their inability to maintain courtship interest. Molecular analysis fails to reveal any defects in the expression of clock components; however, the CREB output is affected. Morphological analysis of neurons required for normal circadian behavior reveals subtle abnormalities, suggesting that defects in axonal pathfinding or synapse formation may cause the observed behavioral defects.

Genetic analysis of Drosophila melanogaster polytene chromosome region 44D-45F: loci required for viability and fertility

A genetic screen to identify mutations in genes in the 45A region on the right arm of chromosome 2 that are involved in oogenesis in Drosophila was undertaken. Several lethal but no female sterile mutations in the region had previously been identified in screens for P-element insertion or utilizing X rays or EMS as a mutagen. Here we report the identification of EMS-induced mutations in 21 essential loci in the 45D-45F region, including 13 previously unidentified loci. In addition, we isolated three mutant alleles of a newly identified locus required for fertility, sine prole. Mutations in sine prole disrupt spermatogenesis at or before individualization of spermatozoa and cause multiple defects in oogenesis, including inappropriate division of the germline cyst and arrest of oogenesis at stage 4.

germ cell-less is required only during the establishment of the germ cell lineage of Drosophila and has activities which are dependent and independent of its localization to the nuclear envelope

The germ cell precursors of Drosophila (pole cells) are specified by maternally supplied germ plasm localized to the posterior pole of the egg. One component of the germ plasm, germ cell-less (gcl) mRNA, encodes a novel protein which specifically localizes to the nuclear envelope of the pole cell nuclei. In addition to its maternal expression, gcl is zygotically expressed through embryonic development. In this report, we have characterized a null allele of germ cell-less to determine its absolute requirement during development. We have found that gcl activity is required only for the establishment of the germ cell lineage. Most embryos lacking maternal gcl activity fail to establish a germline. No other developmental defects were detected. Examination of germline development in these mutant embryos revealed that gcl activity is required for proper pole bud formation, pole cell formation, and pole cell survival. Using this null mutant we have also assayed the activity of forms of Gcl protein with altered subcellular distribution and found that localization to the nuclear envelope is crucial for promoting pole cell formation, but not necessary to initiate and form proper pole buds. These results indicate that gcl acts in at least two different ways during the establishment of the germ cell lineage.