Abstract
The analysis of genes in evolutionarily distant but morphologically similar species is of major importance to unravel the changes in genomes over millions of years, which led to gene silencing and functional diversification. We report the analysis of Wnt8a gene expression in the medakafish and provide a detailed comparison to other vertebrates. In all teleosts analyzed there are two paralogous Wnt8a copies. These show largely overlapping expression in the early developing zebrafish embryo, an evolutionarily distant relative of medaka. In contrast to zebrafish, we find that both maternal and zygotic expression of particularly one Wnt8a paralog has diverged in medaka. While Wnt8a1 expression is mostly conserved at early embryonic stages, the expression of Wnt8a2 differs markedly. In addition, both genes are distinctly expressed during organogenesis unlike the zebrafish homologs, which may hint at the emergence of functional diversification of Wnt8a ligands during evolution.