Expression of ram-5 in the structural cell is required for sensory ray morphogenesis in Caenorhabditis elegans male tail

Tissue morphogenesis requires complex cellular interaction and communicatio n. The sensory ray in the Caenorhabditis elegans male tail has a simple cel lular make-up and a non-essential function, thus providing an ideal model f or studying the mechanisms guiding morphogenesis. We present here the analy sis of a novel gene, ram-5, mutations of which are characterized by abnorma l lumpy rays in the male tail. Microscopic analysis and behavioral studies revealed that lumpy rays contain operational sensory neurons. However, abno rmalities were observed in the hypodermis and structural cells as well as i n appositions between these two cell types. Molecular cloning and expressio n studies revealed that the ram-5 gene encodes a transmembrane protein loca lized in sensory ray support cells, the structural cells. Expression of ram -5 in these cells is required for normal ray morphogenesis, ram-5-dependent cell-cell communication is implicated in organizing the structural cell an d the hypodermis, potentially through adhesion at the structural cell-hypod ermal cell border.