7 Germ-line Development and Fertilization

Abstract

I. INTRODUCTION
Classically, nematode germ cells have provided an excellent source of material for studies of fundamental questions of cell biology. In 1883, Van Beneden used the germ cells of the parasitic nematode, Parascaris equuorum to show that germ cells contain only a haploid number of chromosomes, compared with the diploid number found in somatic cells. This study led Boveri and others to propose that chromosomes are the cellular component that provides genetic continuity from one generation to the next (Wilson 1896). Subsequently, several workers exploited the simplicity and clarity of the cellular architecture of nematode germ cells to explore chromosome structure and the role of the centrosome in cell division.

Today, nematode germ cells continue to provide unique advantages for the study of basic questions of cell biology and development. How is a germ cell signaled to leave the mitotic cell cycle and to enter meiosis? How is a germ cell specified to differentiate as a sperm or as an oocyte? And how is this differentiation carried out? What is the molecular mechanism of ameboid motion? The answers to these questions are beginning to emerge from studies of Caenorhabditis elegans germ cells, using a combination of morphological, genetic, and biochemical approaches.

In this chapter, we cover those aspects of C. elegans germ-line development that are unique to germ-line tissue. These include the processes of spermatogenesis, oogenesis, and fertilization, as well as a discussion of the control of germ-line proliferation and the onset of meiosis. In addition, we summarize our...