Cell-cell signaling plays essential roles in development, homeostasis, and disease, but the physical features of cells that mediate this communication in vivo are surprisingly under-investigated. Dissecting the cell biological processes that regulate intercellular signaling will provide new insights into mechanisms of human diseases and disorders and may suggest new targets for drug discovery. Long-range signaling through many pathways has traditionally been thought to involve diffusion of ligands from signaling to receiving cells, but live imaging of plasma membrane markers has suggested that cryptic cellular extensions sometimes link ligand and receptor expressing cells over long distances, which could provide a diffusion-independent mechanism for long-range signal transduction (1-8). This proposed research utilizes the nematode Caenorhabditis elegans as a tractable system to decipher how cell shapes regulate signal transduction with an emphasis on exploring the roles of cellular extensions in long distance signaling. Specific Aim I will utilize genome engineering and sophisticated live imaging of cell membranes and tagged proteins to identify potential signaling extensions in vivo. Specific Aim II will utilize genome engineering, genetic manipulations, and confocal live imaging to characterize functions for an elaborate set of distal tip cell extensions that may regulate germline stem cell dynamics. The results of these experiments will be assessed by examining effects on germline stem cell maintenance, cell cycles, and differentiation. This work will provide new insights into roles of cryptic cell shapes n development and has great potential to expand our knowledge of cell-cell signaling mechanisms and assess roles of diffusion versus contact-dependent signaling in development.