The control of cell death in the early chick embryo wing bud.

Developmentally programmed cell death occurs in several regions of the chick wing bud. We have studied the nature and control of this cell death in vitro in tissues from two of these regions, the posterior necrotic zone (PNZ) and the opaque patch (OP). When tissue from these regions is excised prior to normal cell death and placed into organ culture, cell death ensues. Under these conditions, cell death in tissue from both of these regions is inhibited by fibroblast growth factor-2 (FGF-2). The only other growth factor we have found to have this function is insulin-like growth factor-II. Cell death in tissue from the OP and PNZ occurs by apoptosis, as indicated by the internucleosomal degradation of DNA and the inhibition of cell death by cycloheximide, an inhibitor of protein synthesis. If cell death is inhibited by FGF-2 and then the growth factor is washed away, a compensatory burst of cell death occurs in the PNZ tissue but not the OP tissue. This finding may indicate that in the PNZ, a death program progresses in the face of FGF-2 inhibition, resulting in more cells on the brink of death when the growth factor is removed.