Localization of expression of Cellular Retinoic Acid Binding Proteins in the early mouse embryo. Strong CRABP immunoreactivity was found in neural crest-derived mesenchyme of the craniofacial area, in visceral arches, in dorsal root ganglia and in cells along the gut and the major vessels of the trunk region. In CNS, CRABP expression and retinoid binding was largely restricted to the hindbrain, to a single layer of the cells in the roof of the midbrain and to cells in the mantle layer of the neural tube.
Two different functions of CRABP have been proposed: CRABP may act as a shuttle, transferring Retinoic Acid (RA) from cytosol to nuclei; or it may compete with the nuclear Receptors from free RA and regulate the intracellular concentration of free RA. [Maden M et all; Domains of cellular retinoic acid-binding protein I (CRABP I) expression in the hindbrain and neural crest of the mouse embryo. Mech Dev 37: 13-23 (1992)]
CRBPs are essential for metabolism of retinoic acid and for maintenance of gradients of retinoic acid in limb buds and neural tube.