Retinoid receptor antagonists alter the pattern of apoptosis in organogenesis stage mouse limbs

Exposure of murine limbs in vitro to vitamin A (retinol) induces limb reduction defects and apoptosis. To assess the relative roles of the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), embryonic-day-12 murine limbs were cultured with selective RAR or RXR antagonists in the presence or absence of teratogenic concentrations of retinol. Both antagonists alone impaired limb development; in the presence of teratogenic concentrations of retinol, both attenuated limb malformations. Abnormal limb morphology, whether caused by excessive or attenuated retinoid signaling by retinol or either antagonist, respectively, was correlated with increased apoptosis after 24 h of drug exposure. We conclude that, in the developing limb, antagonists selective for either member of the RAR/RXR heterodimer attenuate retinoid signaling and block the teratogenic signaling of excess retinol. Improvements in limb morphology in the presence of either the RAR or the RXR antagonist coincided with restoration of the extent and localization of limb bud apoptosis to control patterns.