Genetic Control of Development

Development of a multicellular creature requires not only cell differentiation, but in some cases, cell death. Apoptosis helps create the spaces between the fingers, for instance. During brain development, nerve connections are sculpted through the apoptotic death of billions of cells. In C. elegans, exactly 131 cells die by apoptosis.

Cells can be directed to the apoptotic pathway if they fail to receive appropriate signals from their neighbors. In this way, it is thought that cells in the wrong location—a bone cell in the gut, for instance—might be terminated to prevent damage to the organism. The death program itself is carried out within the cell by activation of specific genes that ultimately trigger proteases, which are enzymes that break down cell contents, including the chromosomes.