11 Spermatogenesis

Abstract

I. OVERVIEW
Spermatogenesis in Caenorhabditis elegans, as in most animals, is a differentiation pathway in which spermatogonial stem cells differentiate into spermatozoa. This process involves mitotic proliferation of spermatogonial cells to form primary spermatocytes and two subsequent meiotic divisions of the nucleus during spermatid formation. Spermiogenesis then follows, which is the maturation of spermatids into spermatozoa. As in other nematodes, C. elegans spermatozoa lack an acrosome and flagellum (for review, see Foor 1983) and move by crawling across the substrate (for review, see Theriot 1996). Although C. elegans sperm differ from flagellated sperm in a number of significant ways, both types of sperm engage in meiosis and in unusual cell divisions characterized by extremely asymmetric cytoplasmic partitioning.

C. elegans offers several advantages over other organisms in which spermatogenesis has been studied. Primary spermatocytes differentiate into spermatids in only 90 minutes and wild-type cells can be easily studied under simple culture conditions in vitro (Ward et al. 1981; L’Hernault and Roberts 1995). Differentiation of spermatocytes into spermatids in vivo is much slower in organisms that produce flagellated sperm, taking about 32 days in humans, 24 days in rats (for review, see Fawcett 1994), and 5 days in Drosophila (Lindsley and Tokuyasu 1980). Although in vitro development of mouse sperm is possible, it has only been attained when germ cells are cocultured with transformed Sertoli-like cells under complex culture conditions (Rassoulzadegan et al. 1993; Hofmann et al. 1994, 1995). Most animals produce sperm that can only be studied by microscopic techniques following...