Apoptosis: Signal Transduction and Modes of Activation

The ability to maintain cellular populations is essential to the proper homeostatic function of organisms. This is accomplished through the finely orchestrated balance of cellular proliferation, differentiation, and death. Beginning early in development, certain cells within a population are chosen to proliferate and differentiate while neighboring cells are selectively deleted from that tissue. An excellent example of this coordinated selection of cellular populations is the embryonic limb bud. The limb bud first forms as a mass of cells with no discernible specialization; however, as differentiation occurs and digits are formed, the cells between the digits die, allowing the paw, or hand, to take shape.