Spatial and temporal pattern of expression of the cellular retinoic acid-binding protein and the cellular retinol-binding protein during mouse embryogenesis.

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Abstract
Retinol (vitamin A) and retinoic acid are potent teratogens and also represent good candidates for normal morphogens during development. Their actions may be mediated by the cellular retinoic acid-binding protein (CRABP) and the cellular retinol-binding protein (CRBP). As a step towards understanding the possible function for CRABP and CRBP in morphogenesis, we have used in situ hybridization to analyze their expression during mouse development. Both CRABP and CRBP transcripts were detected at embryonic days 9.5-14.5. (i) In the nervous system, CRABP transcripts were found in the mantle layer of the dorsal spinal cord and hindbrain and in the marginal layer of the midbrain, whereas CRBP transcripts were found in the ependymal and mantle layer of the ventral spinal cord and of the forebrain as well as in the spinal nerves and the roof plate of the spinal cord. (ii) In the eye, CRABP is expressed in the retinal layer, and CRBP is expressed in both retinal and pigmented layers. (iii) In the craniofacial region, CRABP transcripts were found in the mesenchyme of the frontonasal mass and mandible, while CRBP transcripts were found in the mesenchyme of the nasolachrymal duct and surrounding the auditory vesicle. Two general conclusions can be made. First, all of the tissues that are known to be teratogenic targets of retinoic acid and retinol also express CRABP and CRBP transcripts. Second, the specific expression of CRABP and CRBP in numerous developing tissues indicates that these proteins may perform specific functions during morphogenesis of a broad variety of embryonic structures.