Universal occurrence of the vasa-related genes among metazoans and their germline expression in Hydra

The vasa (vas)-related genes are members of the DEAD box protein family and are involved in germ cell formation in higher metazoans. In the present study, we cloned the vas-related genes as well as the PLIO-related genes, other members of the DEAD box protein family, from lower metazoans: sponge, Hydra and planaria. The phylogenetic analysis suggested that the vas-related genes arose by duplication of a PLIO-related gene before the appearance of sponges but after the diversion of fungi and plants. The vas-related genes in Hydra, Cnvas1 and Cnvas2 were strongly expressed in germline cells and less strongly expressed in multipotent interstitial stem cells and ectodermal epithelial cells. These results suggest that the I as-related genes occur universally among metazoans and that their expression in germline cells was established at least before cnidarian evolution.