Regulation of metamorphic neuronal remodeling by alan shepard (shep).. Dahong Chen, Randall Hewes. Department of Biology, University of Oklahoma, Norman, OK.

   The nervous system undergoes substantial postembryonic remodeling in order to support developmental transitions, responses to environmental changes, and recovery from injury and disease. As a model for understanding the mechanisms governing these changes, we are studying neuronal remodeling during Drosophila metamorphosis. We found that alan shepard (shep) plays an important role in remodeling of peptidergic neurons. shep encodes multiple RNA binding protein isoforms, and it is expressed primarily in the central nervous system. shep mutants displayed multiple defects, including lethality accompanied by failure to evert the head at pupation, blocked wing expansion, reduced lifespan, and sexual rejection of males by virgin females. Based on the wing expansion phenotype, we examined the morphology of the neuropeptidergic neurons that synthesize bursicon, which is an essential regulator of wing expansion behavior. In shep mutants, the bursicon neurons displayed normal cellular morphology in the larval stages, but smaller somata as well as reduced branching and fewer boutons in pharate adults. Expression of a wild-type shep cDNA rescued all of the cellular phenotypes. Interestingly, we found that several other behaviors that appear unrelated to the bursicon neurons (e.g., general locomotion), were largely normal in larvae but often severely impacted in adults. Therefore, shep may play a general role in promoting growth of diverse neurons during metamorphosis. In order to identify the signaling pathway and downstream targets for shep, we analyzed RNA-seq data that were generated by inducing shep^RNAi in S2 cells. Six genes, including 2 endopeptidases, a ribosomal protein, and a lectin, displayed significant changes in expression levels following the loss of shep. To verify the RNA-seq results biologically and identify other candidate interacting genes, we have initiated a genome-wide screen with 777 deficiency stocks for modifiers of the wing expansion defects triggered by shep^RNAi in the bursicon neurons. To date, we have isolated several strong suppressor and enhancer deficiencies.