DEVELOPMENTAL EXPRESSION OF MURINE RETINOID-X-RECEPTOR (RXR) GENES

The developmental expression patterns of the three mouse retinoid X receptor genes (RXR alpha, beta and gamma) have been investigated by Northern blotting and in situ analysis of RNA transcript distribution, and compared to those of retinoic acid receptor (RAR) genes. RXR beta showed a diffuse and probably ubiquitous expression pattern at all developmental stages studied. RXR alpha also exhibited a diffuse expression at early developmental stages, but an enhanced in situ labelling was observed during late development in the epidermis and several other squamous epithelia. By contrast, RXR gamma apparently displayed a restricted expression in the myogenic lineage, i.e. in myotomes and subsequently in various differentiating muscles including those of the face and limbs. Apparently RXR gamma was not co-expressed with RAR beta and RAR gamma in these domains. RXR gamma transcripts were developmentally regulated in the otic epithelium, the retina, the pituitary and thyroid glands. In addition, RXR gamma was expressed in several discrete areas of the fetal central nervous system, namely in the diencephalon, the striatum and in part of the ventral horns of the spinal cord. In the two latter domains, there was a precise co-expression with RAR beta transcripts, although with quantitative differences, which suggests a possible preferential heterodimerization between these two retinoic acid receptors in the developing central nervous system.