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

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 RAR alpha 1, RAR alpha 2, RAR beta 1/3, RAR beta 2/4, RAR gamma 1 and RAR gamma 2 isoform transcripts during mouse embryogenesis. RAR alpha 1 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, RAR alpha 2 is essentially expressed along the spinal cord up to the hindbrain 7th rhombomere and in the 4th rhombomere, pens and developing basal ganglia (corpus striatum and pallidum). RAR beta 2/4 transcripts account for most of the previously described RAR beta expression features being expressed specifically, or more prominently than RAR beta 1/3, in foregut endoderm and its derivatives, olfactory and periocular mesenchyme, urogenital region, proximal limb bud mesenchyme and later within interdigital regions. RAR beta 1/3 is more prominently expressed in the developing heart outflow tract mesenchyme, intervertebral disks, midgut loop mesenchyme and umbilical vessel walls. RAR beta 1/3 and RAR beta 2/4 are coexpressed in the developing corpus striatum. They exhibit, however, distinct dorsoventral distributions along the spinal cord and caudal hindbrain. RAR gamma 2 is the RAR gamma isoform expressed at high levels in the caudal neural groove at embryonic day 8.5. At later stages, both RAR gamma isoforms are essentially coexpressed, although the progressive restriction of RAR gamma 1 transcripts to craniofacial or limb precartilaginous condensations appears to precede that of RAR gamma 2. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.