Census of vertebrate Wnt genes: Isolation and developmental expression of Xenopus Wnt2, Wnt3, Wnt9a, Wnt9b, Wnt10a, and Wnt16

The Wnt family of growth factors regulate many different aspects of embryonic development. Assembly of the complete mouse and human genome sequences, plus expressed sequence tag surveys have established the existence of 19 Wnt genes in mammalian genomes. However, despite the importance of model vertebrates for studies in developmental biology, the complete complement of Wnt genes has not been established for nonmammalian genomes. Using genome sequences for chicken (Gallus gallus), frog (Xenopus tropicalis), and fish (Danio rerio and Tetraodon nigroviridis), we have analyzed gene synteny to identify the orthologues of all 19 human Wnt genes in these species. We find that, in addition to the 19 Wnts observed in humans, chicken contained an additional Wnt gene, Wnt11b, which is orthologous to frog and zebrafish Wnt11 (silberblick). Frog and fish genomes contained orthologues of the 19 mammalian Wnt genes, plus Wnt11b and several duplicated Wnt genes. Specifically, the Xenopus tropicalis genome contained 24 Wnt genes, including additional copies of Wnt7-related genes (Wnt7c) and 3 recent Wnt duplications (Wnt3, Wnt9b, and Wnt11). The Danio rerio genome contained 27 Wnt genes with additional copies of Wnt2, Wnt2b, Wnt4b, Wnt6, Wnt7a, and Wnt8a. The presence of the additional Wnt11 sequence (Wnt11b) in the genomes of all ancestral vertebrates suggests that this gene has been lost during mammalian evolution. Through these studies, we identified the frog orthologues of the previously uncharacterized Wnt2, Wnt3, Wnt9a, Wnt9b, Wnt10a, and Wnt16 genes and their expression has been characterized during early Xenopus development.