DEVELOPMENTAL EXPRESSION AND DIFFERENTIAL REGULATION BY RETINOIC ACIDOF XENOPUS COUP-TF-A AND COUP-TF-B

COUP-TFs (Chicken Ovalbumin Upstream Promoter Transcription Factors) h ave been proposed to be negative regulators of retinoid receptor-media ted transcriptional activation. In a previous paper we reported the cl oning of a Xenopus (x) COUP-TF (Matharu, P.J. and Sweeney, G.E. (1992) Biochim. Biophys. Acta 1129, 331-334). Here we describe the cloning o f a second xCOUP-TF. Amino acid sequence comparison between these two Xenopus COUP-TFs revealed a high level of similarity. Extensive amino acid sequence conservation was found among all Drosophila, Xenopus, ze brafish and mammalian COUP-TF genes examined. Phylogenetic tree analys es indicate that the vertebrate COUP-TFs fall into three classes. The two Xenopus COUP-TF genes show similar temporal expression patterns: b oth are expressed from the end of gastrulation. In situ hybridization studies reveal complex expression patterns in the developing central n ervous system (CNS), besides expression in the eye and in some mesoder mal tissues. Retinoic acid (RA) treatment enhances xCOUP-TF-A expressi on in neurula stage embryos, whereas the expression of xCOUP-TF-B is i nhibited during the same developmental period. The strictly conserved amino acid sequences and the strong similarities between the expressio n patterns of the two different xCOUP-TFs on the one hand, and other v ertebrate COUP-TF homologues on the other, make it likely that COUP-TF s have a conserved role in patterning the nervous system.