Retinoids and mouse placentation

Vitamin A (retinol) and its active acidic derivatives are required for embryonic development in mammals. In order to reach the embryo, the maternally-derived retinol must first pass through the maternal-fetal barrier, the placenta. In the mouse, the placental function is first performed by the yolk sac membrane, which is progressively replaced by a “definitive” chorioallantoic placenta. How retinoids could be involved in the development and function of placental tissues is poorly understood. With the aim of answering this question, we have first studied, throughout mouse gestation, the RNA expression patterns of the various retinol and retinoic acid binding proteins, as well as those of the nuclear retinoic acid receptors, in placental and extraembryonic tissues. Most of the genes analyzed exhibit specific spatio-temporal patterns of expression during both yolk sac and chorioallantoic placentation. In particular, RXRα appears to be the main RXR expressed in the ectoplacental cone and the definitive placenta. As RXRα null mutants die in utero during fetal development, we have characterized the chorioallantoic placental defects exhibited by these mutants. Our results suggest that RXRα plays an important role in the development and function of the murine placenta.