The PDZ-GEF,Gef26 Regulates The Synapse Development And Function In Drosophila NMJ

Guanine nucleotide exchange factor(GEF)is essential for small G protein to switch on downstream signaling pathway,which involved in cell adhesion and migration.GEF transforms small G protein from GDP-binding form to GTP-binding form.Gef26,a PDZ domain contained GEF with a combination of several specific functional domains in Drosophila,has been detected to play roles in wing,eye and the reproductive system development.However,nerve system has rarely been explored so far.Obvious defects of NMJ morphology in Gef26 mutants were observed and only blocking function of Gef26 in neuron could mimic the phenotype.What's more,these defects could be well rescued by over expression of exogenous Gef26,which suggested that Gef26 was essential for normal NMJ morphogenesis.Expressing in nerve system at embryonic stages and similar defects of NMJ since earlier larval stage indicated the role of Gef26 in neurodevelopment.Electrophysiological technique detected functional defects at NMJ and locomotion activity tests showed locomotion deficiency when loss of Gef26 as well.Immunohistochemical staining indicated that increased synaptic FasII,a critical neuronal cell adhesion molecule for NMJ development and remodeling,was responsible for the obviously reduced NMJ size.Immunohistochemical staining,western blot and genetic analyses supplied more evidence to prove that integrin-mediated mechanism regulating local FasII level at NMJ works for Rap1 activated by Gef26 to affect NMJ size.Combining these clues it can be concluded that Gef26 activates its specific small G protein Rap1 to impact on ?PS integrin associated signaling pathway and thus regulates synaptic FasII level to regulate NMJ growth in Drosophila.On the other hand,western blot detected increased phosphorylation of Shaggy,which could regulate axonal microtubule organization to control NMJ growth.Abnormal microtubule cytoskeleton structure in axon observed in Gef26 mutants by immunohistochemical staining with anti-Futsch antibody was similar to that of Wingless.These results imply a connection between the Divergent Wnt Canonical Pathway and Gef26.According to Genetic analyses,Gef26 is likely to work downstream of the receptor Arrow and upstream of Dishevelled in the Divergent Wnt Canonical Pathway.As a result,Gef26 impacts on microtubule organization to regulate NMJ growth.These results can be concluded that Gef26 regulates NMJ growth in two manners.One is through the CAM FasII adjusting cell adhesion,the other is by the Divergent Wnt Canonical Pathway affecting axonal microtubule organization.In our studies Gef26 is proved to participate in nerve system growth in Drosophila,which will provide new clues for researches on nerve system development and neurological diseases.