THE FUNCTIONAL BASIS OF TISSUE-SPECIFIC RETINOIC ACID SIGNALING IN EMBRYOS

Retinoic acid (RA) is essential for normal embryonic development. In m ammals it is sequestered from the maternal circulation in the form of retinol. In rodents, embryonic uptake relies upon the presence of reti nol binding protein (REP) in the yolk sac, probably involving an REP r eceptor. The molecular activity of RA in the nucleus is well establish ed, but less is known about cytoplasmic events including tissue-specif ic intraembryonic RA synthesis and intracellular transport of both ret inol and RA. The cellular binding proteins for retinol and RA may play important roles in these processes.