Genetics of Apoptosis

9.

Programmed cell death in C.elegans

Anton Gartner, Arno Alpi and Björn Schumacher

1.

Introduction

Apoptosis—the term will be used as a synonym for ‘programmed cell death (PCD)’
throughout this chapter—plays a crucial role in animal development and in
maintaining tissue homeostasis. In this chapter, we will review studies on
programined cell death in C. elegans. We will start by summarizing classical studies
that led to the definition of programmed cell death occurring during the development
of C. elegans. We will emphasize the methods that are used to study programmed cell
death in this model organism. In addition, we will describe biochemical interactions
that occur during the execution of programmed cell death in C. elegans, and we will
compare the molecular cell-death pathways in C. elegans to those in mammalian cells.
Furthermore, we will discuss recent developments in the field of C. elegans cell death
that mainly concern the engulfment of apoptotic corpses and the regulation of
programmed cell death in the C. elegans germ line. Finally, we will try to elaborate
on future research directions in the field of C. elegans cell death.

2.

Identity and origin of cells undergoing programmed cell death

during the somatic development of C. elegans

Genetic studies of programmed cell death in C. elegans take advantage of its highly
reproducible and invariant somatic development. This reproducibility allowed the
precise elucidation of the cell lineage that leads, within a time frame of approximately
3 days, to the generation of all of the 959 somatic cells that make up the adult
hermaphrodite worm (Figure 1). Lineage analysis of embryonic and postembryonic
cell-division patterns revealed that during somatic development of the hermaphrodite
worm, 131 out of the total of 1090 cells born undergo programmed cell death (Sulston
and Horvitz, 1977; Kimble and Hirsh, 1979; Sulston et al., 1983). As is true of most
other aspects of C. elegans development, these deaths show a high degree of uniformity
with respect to the identity of dying cells as well as withrespect to the timing of each
of these cell deaths during development. Although the apoptotic fate is restricted