The small soil-living nematode Caenorhabditis elegans is a well-characterized model organism used in the study of genetics and developmental biology. The structure of the male tail of this organism is specialized for locating the hermaphrodite vulva and mating. In the male tail, there are nine pairs of sensory rays embedded in a cuticular fan. The structure of the sensory rays is simple and is composed of three types of cells. In this thesis research, I took advantage of this simple cellular organization of sensory ray and tried to characterize the role of the mab-7 gene in ray morphogenesis....[ Read more ]

The small soil-living nematode Caenorhabditis elegans is a well-characterized model organism used in the study of genetics and developmental biology. The structure of the male tail of this organism is specialized for locating the hermaphrodite vulva and mating. In the male tail, there are nine pairs of sensory rays embedded in a cuticular fan. The structure of the sensory rays is simple and is composed of three types of cells. In this thesis research, I took advantage of this simple cellular organization of sensory ray and tried to characterize the role of the mab-7 gene in ray morphogenesis.

In C. elegans, mutations in a group of ram (r̲ay morphology a̲b̲normal) genes result in sensory ray swelling. Although some of these genes have already been cloned, detailed mechanism guiding this morphogenetic process remains unclear. mab-7 male tail shows similar ray swelling phenotype as that of the ram mutants. The swollen region, however, is localized at the proximal region of the rays. Examination of the cellular defects in the sensory rays uncovered abnormality in all the ray cell components in the mutants. In order to define the role of mab-7 in this ray morphogenetic process, molecular analysis of the gene product was performed.

Cloning and Characterization of mab-7 reveals that this gene encodes a novel secretory protein with an EGF-like domain, an essential ShKT domain and a long C terminus. Expression of this gene has been detected in the hypodermis, structural cells and the body seam. Promoter analyses and the result of ectopic expression of this gene illustrated that the synthesis of this gene product primarily in the hypodermis is important for the ray morphogenesis, while the protein product apparently functions at the extracellular matrix. Domain analyses demonstrated that both of the ShKT domain and the C-terminus are essential for the protein to be functional while the EGF-like domain may be working as a regulatory motif in this protein. Genetic analyses have shown that the ray-swelling phenotype in mab-7 male could be modulated by the genes that are responsible for the matrix production or modification. In addition, genetic interaction between mab-7 and other ram genes provide additional insight on the role of mab-7 in ray morphogenesis.