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Modern Genetic Analysis Chapter 15. Regulation of Cell Number: Normal and Cancer Cells The Machinery or Programmed Cell Death
Genetics In Process 15-2: The nematode Caenorhabditis elegans as a model for programmed cell death

Programmed cell death has been described in a variety of systems. However, genetic studies in the past 10 years in the nematode (roundworm), Caenorhabditis elegans, have propelled the field forward. Researchers have mapped the entire series of somatic cell divisions that produce the 1000 or so cells of the adult worm. Interestingly, for some of the embryonic and larval cell divisions, particularly those that will contribute to the worm's nervous system, a progenitor cell gives rise to two progeny cells, one of which then undergoes programmed cell death (see the adjoining figure). These divisions, in which one progenitor cell gives rise to only one viable progeny cell, are necessary for the progeny cell to fulfill its proper developmental role.

A set of mutations have been identified in the worm that block this cell death phenotype. Some of these mutations knock out the functions of genes that encode caspases. An example is ced-3 (cell death gene number 3), clearly implicating these caspases in the apoptosis process. The analysis of other genes with mutant cell death pheno-types is being carried out in worms and other experimental systems and is uncovering other key players in this process.

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