Patterns of physiological cell death and mitoses in the apical ectodermal ridge in normodactylous and polydactylous rat limb buds. A quantitative evaluation.

Limb buds in normally developing foetal rats and rats with the polydactyly-luxate syndrome at day 14 and 15 of intrauterine growth were studied at the optical and electron microscopic levels. Four sets of limb buds were collected and evaluated: 14th e.d.N., 14th e.d.P., 15th e.d.N., and 15th e.d.P. (e.d. embryonic day, N - normodactylous, P - polydactylous); they were studied for apical ectodermal ridge development with reference to the rates of cell death and mitosis. Both phenomena were evaluated quantitatively. A significant difference was found in the rate of physiological cell death, which was far lower in polydactylous (4.33 and 28.73) as compared with normodactylous individuals (62.40 and 82.11 cell deaths per 300 cells in the ridge on days 14 and 15). The difference found documents a considerable retardation in cell death rate in the polydactylous apical ectodermal ridge epithelium. Physiological cell death is associated with a process called apoptosis, which is characterized by the presence of "apoptotic bodies" in the cytoplasm of epithelial cells and in the intercellular space. The total number of mitoses in the ridge epithelium was relatively low (4.63 - 6.33 per 300 cells) and the differences between norm and polydactyly were not statistically significant.