Embryonic expression patterns of Eukaryotic EndoU ribonuclease family gene endouC in zebrafish.

Endou proteins belong to the Eukaryotic EndoU ribonuclease family of enzymes that present high sequence homology with the founding member XendoU domain. The enzymatic activity and three-dimensional structure of some Endou proteins have been previously reported. However, their molecular structure and gene expression patterns during embryogenesis remain to be elucidated. Therefore, we took zebrafish (Danio rerio) endouC as the model to study molecular structure and gene expression dynamics at different developmental stages. Zebrafish endouC cDNA contains 930 base pairs encoding 309 amino acid residues, sharing 27%, 27%, 27%, and 25% identity with that of human, mouse, chicken and frog, respectively. A phylogenetic tree showed that zebrafish EndouA was clustered with vertebrate Endou groups, while zebrafish EndouB and EndouC were found to belong to a unique monophyletic group. Furthermore, the endouC transcript was detected in one-cell embryos, suggesting that it is a maternal gene. While the endouC transcript was only weakly present at early developmental stages, its expression was greatly increased in embryos from 18 to 48 h post-fertilization (hpf) and then decreased after 72 hpf. Finally, endouC was ubiquitously expressed throughout the whole embryo during early embryogenesis, but its expression was enriched in brain, eyes and fin buds from 24 to 96 hpf.