Two isoforms of retinoic acid receptor alpha expressed during Xenopus development respond to retinoic acid.

Retinoic acid regulates gene expression by binding to receptors that are ligand-dependent transcription factors. The different types of RARs may mediate the diverse effects of RA on different tissues at different stages of development. This implies RAR expression will be spatially and temporally regulated during normal development. To examine this point, cDNA clones encoding RARs have been isolated from Xenopus embryos. Two different classes of RAR alpha have been characterised, they both show most similarity to the RAR alpha 2 isoform. In response to exogenous RA, XRAR alpha 2 transcripts accumulate whilst the level of XRAR gamma decreases. In addition, transcripts from the two XRAR alpha 2 genes are differentially distributed in the neurectoderm of RA treated embryos. Modulation of RAR transcript levels by RA may provide one level of control of RAR gene expression during development.