RETINOIDS AND THEIR RECEPTORS IN VERTEBRATE EMBRYOGENESIS

Vitamin A and its derivatives, the retinoids, participate in formation of diverse embryonic structures, including face, heart, eye, limb and nervous system. Studies of retinoid-deficient and -treated embryos, a nd of receptor null mutants, provide evidence that this participation involves interactions between retinoids and their receptors. Targeted retinoid application and retinoid deficiency, using in ovo avian embry os, has identified early cardiogenic contributions, including cardiocy te gene expression and differentiation, heart tube fusion and laterali ty, and segmental identity, Also useful is a mammalian model, which ta rgets retinoid deficiency to distinct gestational windows, circumventi ng limitations of traditional deficiency studies and current null muta nt technologies, Rat embryos made deficient in retinoids during gestat ional d 11.5-13.5 exhibit specific cardiac, limb, ocular and nervous s ystem deficits, That many of the anomalies previously reported in reti noid receptor null mutants are observed in deficiency confirms that li gand-receptor interactions are essential for embryonic development, Ot her defects are novel, reemphasizing the functional redundancy of reti noid receptors and that retinoid receptors have multiple and overlappi ng contributions to morphogenesis.