Developmental expression and differential regulation by retinoic acid ofXenopus COUP-TF-A andCOUP-TF-B

COUP-TFs (Chicken Ovalbumin Upstream Promoter Transcription Factors) have been proposed to be negative regulators of retinoid receptor-mediated transcriptional activation. In a previous paper we reported the cloning of aXenopus (x) COUP-TF (Matharu, P.J. and Sweeney, G.E. (1992) Biochim. Biophys. Acta 1129, 331–334). Here we describe the cloning of a secondxCOUP-TF. Amino acid sequence comparison between these twoXenopus COUP-TFs revealed a high level of similarity. Extensive amino acid sequence conservation was found among allDrosophila, Xenopus, zebrafish and mammalianCOUP-TF genes examined. Phylogenetic tree analyses indicate that the vertebrate COUP-TFs fall into three classes. The twoXenopus COUP-TF genes show similar temporal expression patterns: both are expressed from the end of gastrulation. In situ hybridization studies reveal complex expression patterns in the developing central nervous system (CNS), besides expression in the eye and in some mesodermal tissues. Retinoic acid (RA) treatment enhancesxCOUP-TF-A expression in neurula stage embryos, whereas the expression ofxCOUP-TF-B is inhibited during the same developmental period. The strictly conserved amino acid sequences and the strong similarities between the expression patterns of the two differentxCOUP-TFs on the one hand, and other vertebrateCOUP-TF homologues on the other, make it likely that COUP-TFs have a conserved role in patterning the nervous system.