Methods for studying programmed cell death in C. elegans.

Programmed cell death or apoptosis is a common cell fate during the development of multicellular organisms, including C. elegans. C. elegans has been proven to be an excellent model organism for studies of programmed cell death. Its transparency and the knowledge of its cell lineage, including its invariant life vs. death fate of all cells, allow programmed cell death to be studied in vivo at single cell resolution in a way that no other systems can currently match. This advantage, in combination with sophisticated genetic manipulations, has facilitated the identification and characterization of many genes important for different aspects of programmed cell death. In addition to the ability to observe life and death of cells directly under Nomarski optics or by using fluorescent transgene products in living animals, several methods have been developed to study other aspects of apoptosis. For example, fragmentation of chromosomal DNA and the identity of phagocytic cells that engulf cell corpses can be analyzed using specific staining methods. Proteases and nucleases involved in cell killing and DNA degradation, respectively, can be studied using specific biochemical assays. These cell death assays have been instrumental in elucidating the functions of cell death-related genes and the mechanisms by which they affect cell death. In this chapter, we will review and describe these methods in detail.