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Comments on Baird SE et al. (1991) International C. elegans Meeting "CELLULAR EVENTS DETERMINlNG THE ARRANGEMENT OF RAYS IN THE C. ELEGANS MALE TAIL." (0)
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Baird SE, Fitch DHA, Kassem IAA, & Emmons SW (1991). CELLULAR EVENTS DETERMINlNG THE ARRANGEMENT OF RAYS IN THE C. ELEGANS MALE TAIL presented in International C. elegans Meeting. Unpublished information; cite only with author permission.
Nine pairs of peripheral sense organs known as rays are present at reproducible positions in the fan of the C. elegans male tail. Each ray has a defined anteroposterior and dorsoventral position, and the overall pattern differs subtly between related species, indicating that the arrangement is genetically specified. We have shown that the arrangement of the rays is determined by interactions between ray cells-and epidermal cells during the L4 larval stage, and have identified mutations in 6 genes that define components of an active morphogenetic mechanism. A key element of the mechanism appears to be the specification of distinct ray identities, such that each ray expresses different morphogenetic properties. The fan and rays form during an anterior retraction of cells in the L4 male tail. Prior to this retraction, ray structural cells attach to the adult cuticle at specific sites, and these sites determine the final position of each ray in the adult fan. We have described the shapes, positions, and contacts of cells in the posterior epidermis by indirect immunofluorescence staining of cell boundaries with the monoclonal antibody MH27 of R. Waterston and colleagues. We have shown that epidermal cells generated by the ray sublineage (Rn.p cells) undergo a complex series of shape changes, movements, and fusions during the L4. Ray cells, which are born in the epidermis, exhibit at least three types of cellular interactions leading to their assumption of specific positions within the pattern of epidermal cells: they associate together and reject associations with cells of neighboring rays, they make contacts with specific sets of epidermal cells, and, in the case of rays 1, 2, and 4, they undergo selective engulfment by epidermal cells. Phenotypes of mutations causing fusion of rays and alteration of ray attachment sites in the L4 confirm the conclusion that the position of a ray in the adult is determined by the position where the ray cell attaches to the cuticle in the L4. These mutations are interpreted as either affecting the establishment of distinct ray identities, or as preventing specific morphogenetic interactions. A key step blocked in some mutants appears to be the separate fasciculation of processes belonging to individual rays.