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 communication. The sensory ray in the Caenorhabditis elegans male tail has a simple cellular make-up and a non-essential function, thus providing an ideal model for studying the mechanisms guiding morphogenesis. We present here the analysis of a novel gene, ram-5, mutations of which are characterized by abnormal lumpy rays in the male tail. Microscopic analysis and behavioral studies revealed that lumpy rays contain operational sensory neurons. However, abnormalities were observed in the hypodermis and structural cells as well as in appositions between these two cell types. Molecular cloning and expression studies revealed that the ram-5 gene encodes a transmembrane protein localized 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 and the hypodermis, potentially through adhesion at the structural cell-hypodermal cell border.