Retinoic-acid-induced limb-reduction defects: perturbation of zones of programmed cell death as a pathogenetic mechanism.

Pregnant C57Bl/6J mice were treated with 100 mg/kg body weight of all-trans retinoic acid in sesame oil on day 11.0 of gestation. Among the live fetuses harvested on day 18 of gestation, 100% had mesomelic defects of the limbs as determined by gross examination and skeletal staining. Control fetuses treated with sesame oil had no observable limb malformations. Some treated and control embryos were harvested 12 hr after treatment and examined for patterns of cell death by using the supravital stain Nile blue sulphate and methylene-blue- and acid-fuchsin-stained histological sections. Retinoic-acid-induced cell death in the core of the limb was always associated with the zones of programmed cell death as seen in control embryos of comparable stages. This, in concert with previous studies demonstrating excessive cell death in regions of programmed cell death that correlated with subsequent malformations, leads us to conclude that the pathogenesis of mesomelic malformations has a primary association with the phenomenon of programmed cell death.