Functional Roles of spe Genes in the Male Germline During Reproduction of Caenorhabditis elegans

Abstract

The nematode Caenorhabditis elegans is an excellent model animal to study various biological phenomena, including reproduction. In this chapter, we focus on functional roles of spermatogenesis- or sperm-defective (spe) genes in the C. elegans male germline during reproduction. So far, approximately 190 mutants of C. elegans that are defective in male germline functions have been isolated, and many of them carry mutated alleles for one of the perhaps 60 spe genes. Most spe genes exhibit male germline-specific expression and play roles during spermatogenesis (spermatid production), spermiogenesis (spermatid activation into sperm), or fertilization. For example, spe-8 class genes are indispensable for hermaphrodite-dependent spermiogenesis. If either of the spe-8 class genes is aberrant, spermatids from mutant hermaphrodites, but not from males, arrest at an intermediate stage during spermiogenesis. In contrast, fertilization requires spe-9 class genes. Hermaphrodites and males of spe-9 class mutants produce otherwise normal sperm that are incapable of fertilizing oocytes. Because C. elegans oocytes have no egg coats, spe-9 class genes are probably required for sperm to bind to and/or fuse with the oocyte plasma membrane. Intriguingly, several spe genes are likely to be orthologues of mammalian genes, suggesting that C. elegans and mammals share some common steps during male germline functions at the molecular level.