that stain brightly are the ones with large numbers of 3_ ends. If there's no bright stain, there's no apoptosis," comments Busser. Apoptosis as part of normal development is a strategy to select certain cells for survival, sculpting a tissue's specificity. In a vertebrate embryo's limb, apoptosis carves fingers from webbing. In the developing brain it leaves behind only certain neural connections, and in the fetal thymus allows only T cells with "self" surfaces to complete development. Later in life, apoptosis protects. Consider sunburn. A cell whose DNA is damaged by ultraviolet radiation in sunlight is either repaired or jettisoned via apoptosis--peeling (A. Ziegler et al., Nature, 372:773-6, 1994). "Such controls ensure that any one mutated cell cannot proliferate. Without this, tumors would be incredibly common," Green explains. Developmental biologists have long been familiar with cell death in carving a vertebrate's digits and in insect metamorphosis. But today's cell-death community credits a paper by University of Edinburgh researcher Andrew Wyllie and his colleagues as the seminal work in the field (J.F.R. Kerr, A.H. Wyllie, A.R. Currie, British Journal of Cancer, 26:239-57, 1972). They coined the term apoptosis, writing that it plays "a complementary but opposite role to mitosis in the regulation of animal cell populations." The paper created little excitement initially. "It was just one of those things in the literature that stayed dormant for 10 to 15 years. Then it was gradually rediscovered and gained recognition as a generally important mechanism," reports L. Maximilian Buja, chairman of the department of pathology and laboratory medicine at the University of Texas Medical School at Houston. What catapulted apoptosis into "hot topic" status was its meticulous demonstration in a tiny worm, followed by identification of death genes in other organisms (J. Sulston, H.R. Horvitz, Developmental Biology, 56:110-56, 1977). In t...
