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

The three murine retinoic acid receptor (RAR) genes each contain two distin ct promoters which give rise to protein isoforms differing in their N-termi nal regions. This study used in situ hybridization to describe the expressi on patterns of RAR alpha 1, RAR alpha 2, RAR beta 1/3, RAR beta 2/4, RAR ga mma 1 and RAR gamma 2 isoform transcripts during mouse embryogenesis. RAR a lpha 1 transcripts are widely distributed, with the exception of the centra l nervous system. Highest expression is found in developing muscle, pituita ry gland and various epithelia. On the other hand, RAR alpha 2 is essential ly expressed along the spinal cord up to the hindbrain 7th rhombomere and i n the 4th rhombomere, pens and developing basal ganglia (corpus striatum an d pallidum). RAR beta 2/4 transcripts account for most of the previously de scribed RAR beta expression features being expressed specifically, or more prominently than RAR beta 1/3, in foregut endoderm and its derivatives, olf actory and periocular mesenchyme, urogenital region, proximal limb bud mese nchyme and later within interdigital regions. RAR beta 1/3 is more prominen tly expressed in the developing heart outflow tract mesenchyme, interverteb ral 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 ex hibit, however, distinct dorsoventral distributions along the spinal cord a nd 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 progressi ve restriction of RAR gamma 1 transcripts to craniofacial or limb precartil aginous condensations appears to precede that of RAR gamma 2. (C) 2000 Else vier Science Ireland Ltd. All rights reserved.