Molecular and genetic analysis of spermatogenesis in Caenorhabditis elegans.

Abstract

For cells to function in a complex organism, they must differentiate and acquire their specific morphology. To study how cells achieve this I have chosen the spermatozoon of the nematode Caenorhabditis elegans. Genes involved in virtually every step of sperm development have been identified by mutations in C. elegans and these mutations dissect the process of differentiation. During spermiogenesis spherical non-motile spermatids differentiate into bipolar amoeboid spermatozoa. Chapters II and III describe the characterization of two genes that affect this differentiation. For both genes, spe-27 and spe-12, mutant hermaphrodites are sterile whereas mutant males are fertile, and spermatids only activate in response to a subset of in vivo and in vitro activators. I present a detailed genetic, phenotypic and molecular analysis of spe-27 mutants. Spe-27 maps to chromosome IV between two previously cloned genes, so I could isolate and sequence a genomic clone containing spe-27 by transformation rescue with clones from the physical map. The protein sequence predicted from the genomic and cDNA sequences shows no significant similarity with currently known proteins. Three mutant alleles were found to be two splicing defects and a missense mutation. Differential northern analysis and in situ hybridizations indicate that spe-27 is expressed in spermatocytes. I propose a model for spermatid activation in which the spe-27 gene product is a member of a signaling pathway necessary for hermaphrodite sperm activation, and present but redundant in the males. I hypothesize that the spe-12 gene product is another member of the signaling pathway necessary for hermaphrodite spermiogenesis. I isolated six new spe-12 alleles. Chapter IV describes collaborative research to characterize the spe-6 gene, which is involved in the localization of sperm-specific proteins to specialized organelles at the spermatocyte stage. The spe-6 gene shows second site non-complementation with an unlinked deficiency, which suggests the presence of interacting gene(s) over that deficiency. I also collaborated on research on the spe-26 gene, but that work is not included in this dissertation.