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Submitted on April 26, 2005
Accepted on July 14, 2005
Department of Ecology and Evolutionary Biology, Department of Molecular, Cellular and Developmental Biology The University of Michigan, Ann Arbor, MI 48109-1048; Johnson & Johnson, Research & Development, CNS Research, Turnhoutseweg 30, Building 020, Room 1L6 B-2340 Beerse, Belgium
* To whom correspondence should be addressed. E-mail: rdenver{at}umich.edu.
Several corticotropin-releasing factor (CRF) family genes have been identified in vertebrates. Mammals have four paralogous genes that encode CRF or the urocortins 1, 2 and 3. In teleost fishes a CRF, urotensin I (a fish ortholog of mammalian urocortin 1) and urocortin 3 have been identified, suggesting that at least three of the four mammalian lineages arose in a common ancestor of modern bony fishes and tetrapods. Here we report the isolation of genes orthologous to mammalian urocortin 1 and urocortin 3 from the South African clawed frog, Xenopus laevis. We characterized the pharmacology of the frog peptides and show that X. laevis urocortin 1 binds to and activates the frog CRF1 and CRF2 receptors at picomolar concentrations. Similar to mammals, frog urocortin 3 is selective for the CRF2 receptor. Only frog urocortin 1 bound to the CRF-binding protein, although with significantly lower affinity than frog CRF. Both urocortin genes are expressed in brain, pituitary, heart, and kidney of juvenile frogs; urocortin 1 is also expressed in skin. We also identified novel urocortin sequences in the genomes of pufferfish, zebrafish, chicken and dog. Phylogenetic analysis supports the view that four paralogous lineages of CRF-like peptides arose before the divergence of the actinopterygian and sarcopterygian fishes. Our findings show that the functional relationships among CRF ligands and binding proteins, and their anorexigenic actions mediated by the CRF2 receptor arose early in vertebrate evolution.
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