Tissue-specific expression of retinoic acid receptor isoform transcripts in the mouse embryo

Abstract The three murine retinoic acid receptor (RAR) genes each contain two distinct promoters which give rise to protein isoforms differing in their N-terminal regions. This study used in situ hybridization to describe the expression patterns of RARα1, RARα2, RARβ1/3, RARβ2/4, RARγ1 and RARγ2 isoform transcripts during mouse embryogenesis. RARα1 transcripts are widely distributed, with the exception of the central nervous system. Highest expression is found in developing muscle, pituitary gland and various epithelia. On the other hand, RARα2 is essentially expressed along the spinal cord up to the hindbrain 7th rhombomere and in the 4th rhombomere, pons and developing basal ganglia (corpus striatum and pallidum). RARβ2/4 transcripts account for most of the previously described RARβ expression features being expressed specifically, or more prominently than RARβ1/3, in foregut endoderm and its derivatives, olfactory and periocular mesenchyme, urogenital region, proximal limb bud mesenchyme and later within interdigital regions. RARβ1/3 is more prominently expressed in the developing heart outflow tract mesenchyme, intervertebral disks, midgut loop mesenchyme and umbilical vessel walls. RARβ1/3 and RARβ2/4 are coexpressed in the developing corpus striatum. They exhibit, however, distinct dorsoventral distributions along the spinal cord and caudal hindbrain. RARγ2 is the RARγ isoform expressed at high levels in the caudal neural groove at embryonic day 8.5. At later stages, both RARγ isoforms are essentially coexpressed, although the progressive restriction of RARγ1 transcripts to craniofacial or limb precartilaginous condensations appears to precede that of RARγ2.