Drosophila RhoGEF4 encodes a novel RhoA-specific guanine exchange factor that is highly expressed in the embryonic central nervous system

Systematic analysis of RhoGEF/GAP localizations uncovers regulators of mechanosensing and junction formation during epithelial cell division

Cell proliferation is central to epithelial tissue development, repair, and homeostasis. During cell division, small RhoGTPases control both actomyosin dynamics and cell-cell junction remodeling to faithfully segregate the genome while maintaining tissue polarity and integrity. To decipher the mechanisms of RhoGTPase spatiotemporal regulation during epithelial cell division, we generated a transgenic fluorescently tagged library for the 48 Drosophila Rho guanine exchange factors (RhoGEFs) and GTPase-activating proteins (GAPs), and we systematically characterized their endogenous distributions by time-lapse microscopy. Therefore, we unveiled candidate regulators of the interplay between actomyosin and junctional dynamics during epithelial cell division. Building on these findings, we established that the conserved RhoGEF Cysts and RhoGEF4 play sequential and distinct roles to couple cytokinesis with de novo junction formation. During ring contraction, Cysts via Rho1 participates in the neighbor mechanosensing response, promoting daughter-daughter cell membrane juxtaposition in preparation to de novo junction formation. Subsequently and upon midbody formation, RhoGEF4 via Rac acts in the dividing cell to ensure the withdrawal of the neighboring cell membranes, thus controlling de novo junction length and cell-cell arrangements upon cytokinesis. Altogether, our findings delineate how the RhoGTPases Rho and Rac are locally and temporally activated during epithelial cytokinesis, highlighting the RhoGEF/GAP library as a key resource to understand the broad range of biological processes regulated by RhoGTPases.

The PH Domain and C-Terminal polyD Motif of Phafin2 Exhibit a Unique Concurrence in Animals

Phafin2, a member of the Phafin family of proteins, contributes to a plethora of cellular activities including autophagy, endosomal cargo transportation, and macropinocytosis. The PH and FYVE domains of Phafin2 play key roles in membrane binding, whereas the C-terminal poly aspartic acid (polyD) motif specifically autoinhibits the PH domain binding to the membrane phosphatidylinositol 3-phosphate (PtdIns3P). Since the Phafin2 FYVE domain also binds PtdIns3P, the role of the polyD motif remains unclear. In this study, bioinformatics tools and resources were employed to determine the concurrence of the PH-FYVE module with the polyD motif among Phafin2 and PH-, FYVE-, or polyD-containing proteins from bacteria to humans. FYVE was found to be an ancient domain of Phafin2 and is related to proteins that are present in both prokaryotes and eukaryotes. Interestingly, the polyD motif only evolved in Phafin2 and PH- or both PH-FYVE-containing proteins in animals. PolyD motifs are absent in PH domain-free FYVE-containing proteins, which usually display cellular trafficking or autophagic functions. Moreover, the prediction of the Phafin2-interacting network indicates that Phafin2 primarily cross-talks with proteins involved in autophagy, protein trafficking, and neuronal function. Taken together, the concurrence of the polyD motif with the PH domain may be associated with complex cellular functions that evolved specifically in animals.

MiRNA-190 exerts neuroprotective effects against ischemic stroke through Rho/Rho-kinase pathway

Ischemic stroke is an urgent public health concern and one of the major causes of deaths and disabilities over the world. MicroRNA (miRNA) has become a key mediator of cerebral ischemia-reperfusion (I/R) injuries. However, whether miR-190 is involved in cerebral I/R-induced neuronal damage remains unknown. This study was to investigate the role of miR-190 in the brain I/R injury. We divided the rats into sham, I/R, control, and miR-190-mim (miR-190 mimics) groups. Quantitative real-time polymerase chain reaction (qRT-PCR), Nissl staining, flow cytometry, and western blot were conducted to examine the expression of miR-190 and cell apoptosis in different groups. The results showed that the expression of miR-190 was greatly decreased in rats suffering with I/R. Overexpression of miR-190 significantly reduced the increased neurological scores, brain water contents, infarct volumes, and neuronal apoptosis in rats suffering with I/R. In addition, we found that the expression of RhoA and Rho kinase was greatly elevated in rats suffering with I/R. Bioinformatics analysis indicated that Rho was a target of miR-190. Moreover, overexpression of miR-190 significantly downregulated the increased mRNA and protein expression of Rho/Rho kinase and cell apoptosis, while inhibition of miR-190 further upregulated the increased mRNA and protein expression of Rho/Rho kinase and cell apoptosis in rats suffering with I/R. Furthermore, knockdown of Rho significantly downregulated the increased mRNA and protein expression of Rho/Rho kinase and cell apoptosis, while these effects were inhibited by miR-190 inhibitors in rats suffering with I/R. These results indicate that miR-190 confers protection against brain I/R damage by modulating Rho/Rho-kinase signaling.

Mask, a component of the Hippo pathway, is required for Drosophila eye morphogenesis

Hippo signaling is an important regulator of tissue size, but it also has a lesser-known role in tissue morphogenesis. Here we use the Drosophila pupal eye to explore the role of the Hippo effector Yki and its cofactor Mask in morphogenesis. We found that Mask is required for the correct distribution and accumulation of adherens junctions and appropriate organization of the cytoskeleton. Accordingly, disrupting mask expression led to severe mis-patterning and similar defects were observed when yki was reduced or in response to ectopic wts. Further, the patterning defects generated by reducing mask expression were modified by Hippo pathway activity. RNA-sequencing revealed a requirement for Mask for appropriate expression of numerous genes during eye morphogenesis. These included genes implicated in cell adhesion and cytoskeletal organization, a comprehensive set of genes that promote cell survival, and numerous signal transduction genes. To validate our transcriptome analyses, we then considered two loci that were modified by Mask activity: FER and Vinc, which have established roles in regulating adhesion. Modulating the expression of either locus modified mask mis-patterning and adhesion phenotypes. Further, expression of FER and Vinc was modified by Yki. It is well-established that the Hippo pathway is responsive to changes in cell adhesion and the cytoskeleton, but our data indicate that Hippo signaling also regulates these structures.

Characterization of the Rho GTPase-Activating Protein RhoGAP68F

Rho small GTPases control multiple aspects of neuronal morphogenesis by regulating the assembly and organization of the actin cytoskeleton. Although they are negatively regulated by GTPase activating proteins (GAPs), the roles of RhoGAPs in the nervous system have not been fully investigated. Here we describe a characterization of Drosophila RhoGAP68F that is mainly expressed in the embryonic central nervous system. RNA in situ hybridization analysis showed that expression of RhoGAP68F is highly restricted to the embryonic brain and ventral nerve cord. Database search revealed that RhoGAP68F contains an N-terminal Sec14 domain and a C-terminal RhoGAP domain. Rho-GTP pull-down assay demonstrated that the RhoGAP domain of RhoGAP68F inactivates RhoA but not Rac1 or Cdc42 in HEK293 cells. In addition, expression of RhoGAP68F in NIH3T3 cells suppressed LPA-induced stress fiber formation, which is mediated by RhoA. Finally, neuronal overexpression of RhoGAP68F causes synaptic overgrowth at the larval neuromuscular junction (NMJ). Taken together, these results suggest that RhoGAP68F may play a role in synaptic growth regulation by inactivating RhoA.

Genes encoding novel secreted and transmembrane proteins are temporally and spatially regulated during Drosophila melanogaster embryogenesis

BACKGROUND

Morphogenetic events that shape the Drosophila melanogaster embryo are tightly controlled by a genetic program in which specific sets of genes are up-regulated. We used a suppressive subtractive hybridization procedure to identify a group of developmentally regulated genes during early stages of D. melanogaster embryogenesis. We studied the spatiotemporal activity of these genes in five different intervals covering 12 stages of embryogenesis.

RESULTS

Microarrays were constructed to confirm induction of expression and to determine the temporal profile of isolated subtracted cDNAs during embryo development. We identified a set of 118 genes whose expression levels increased significantly in at least one developmental interval compared with a reference interval. Of these genes, 53% had a phenotype and/or molecular function reported in the literature, whereas 47% were essentially uncharacterized. Clustering analysis revealed demarcated transcript groups with maximum gene activity at distinct developmental intervals. In situ hybridization assays were carried out on 23 uncharacterized genes, 15 of which proved to have spatiotemporally restricted expression patterns. Among these 15 uncharacterized genes, 13 were found to encode putative secreted and transmembrane proteins. For three of them we validated our protein sequence predictions by expressing their cDNAs in Drosophila S2R+ cells and analyzed the subcellular distribution of recombinant proteins. We then focused on the functional characterization of the gene CG6234. Inhibition of CG6234 by RNA interference resulted in morphological defects in embryos, suggesting the involvement of this gene in germ band retraction.

CONCLUSION

Our data have yielded a list of developmentally regulated D. melanogaster genes and their expression profiles during embryogenesis and provide new information on the spatiotemporal expression patterns of several uncharacterized genes. In particular, we recovered a substantial number of unknown genes encoding putative secreted and transmembrane proteins, suggesting new components of signaling pathways that might be incorporated within the existing regulatory networks controlling D. melanogaster embryogenesis. These genes are also good candidates for additional targeted functional analyses similar to those we conducted for CG6234.See related minireview by Vichas and Zallen: http://www.jbiol.com/content/8/8/76.

The nuclear factor kappaB-activator gene PLEKHG5 is mutated in a form of autosomal recessive lower motor neuron disease with childhood onset

Lower motor neuron diseases (LMNDs) include a large spectrum of clinically and genetically heterogeneous disorders. Studying a large inbred African family, we recently described a novel autosomal recessive LMND variant characterized by childhood onset, generalized muscle involvement, and severe outcome, and we mapped the disease gene to a 3.9-cM interval on chromosome 1p36. We identified a homozygous missense mutation (c.1940 T-->C [p.647 Phe-->Ser]) of the Pleckstrin homology domain-containing, family G member 5 gene, PLEKHG5. In transiently transfected HEK293 and MCF10A cell lines, we found that wild-type PLEKHG5 activated the nuclear factor kappa B (NF kappa B) signaling pathway and that both the stability and the intracellular location of mutant PLEKHG5 protein were altered, severely impairing the NF kappa B transduction pathway. Moreover, aggregates were observed in transiently transfected NSC34 murine motor neurons overexpressing the mutant PLEKHG5 protein. Both loss of PLEKHG5 function and aggregate formation may contribute to neurotoxicity in this novel form of LMND.