Identification and Molecular Characterization of dveli, the drosophila ortholog of C. Elegans lin-7

Abstract

Receptors and signal transduction complexes are assembled in a precise manner at specific subdomains of the plasma membrane. Recent research has implicated scaffolding proteins in organizing these receptor and signaling complexes. One well characterized example is the C. elegans LIN-2/LIN-7 /LIN-1 0 complex. This complex is essential in the proper localization of LET -23, the EGFR ortholog, to the basolateral membrane surface of vulval epithelial cells. The mammalian orthologs of the LIN-2/LIN-7 /LIN-10 complex have been identified. CASKIVELI!Mintl/Xllalpha function as a tripartite complex in neurons, presynaptically and postsynaptically. Presynaptically, the multi protein complex aids in linking cell adhesion to ion influx, synaptic vesicle fusion with the presynaptic membrane. and subsequent neurotransmitter release. At the post-synaptic membrane, the CASKIVELI!Mintl/Xllalpha complex is hypothesized to function in the sorting and proper localization of the NMDA type glutamate receptor, reflecting the function of the C. elegans orthologs in receptor localization. We have identified the Drosophila orthologs ofLIN-2/CASK, LIN-7NELI, and LIN-10/Mintl/Xllalpha, termed CMG, dVELI and dMINT. respectively. These proteins were found to be highly conserved among species. The Drosophila YELl protein was initially identified by the McGlade laboratory, University of Toronto, where it was found to bind phosphorylated Drosophila EGFR (DER). We have mapped the chromosomal location of dveli, determined RNA transcript distribution and protein localization, and initiated a P-element mutagenesis screen to generate a dveli mutant. Furthermore, candidate genes for other proteins known to associate with LIN-7 (PALS) have been identified by sequence analysis. dVELI expression begins early in the larval stage. It is concentrated mostly in neuropil areas, sites of synaptic connections. This expression pattern continues into adult development. Within the larval CNS, dVELI protein is localized to the neuropil areas of the ventral nerve cord and brain. NMJ staining further localizes dVELI almost exclusively to the post-synaptic density. This post-synaptic localization resembles that of mammalian YELls, wherein the complex is thought to aid in glutamate receptor sorting and localization. The similarity in structure and expression patterns of dVELI to that of its mammalian orthologs suggests a model in which the Drosophila complex aids in the localization of receptors to post -synaptic specializations in neurons.