Abstract
The ribonuclease (RNase) A superfamily is a vertebrate-specific gene family, whose members are associated with various biochemical and physiological functions including host defense. It has been known that non-mammalian vertebrates, such as fish and birds, have relatively fewer RNase genes than placental and marsupial mammals, suggesting that the superfamily experienced an expansion during early mammalian evolution. However, it is still unclear when the expansion occurred and how various extant subfamilies were formed during the expansion by gene duplication. To answer these questions, we implemented a comparative, evolutionary genomics approach to determine the RNase A superfamily repertoires of a wide variety of placental mammals and platypus, a monotreme, covering the entire spectrum of the mammalian class. Using the gene sequences we made from various databases such as NCBI and ENSEMBL, we construct phylogenetic trees of the mammalian RNase genes to elucidate how the superfamily diversified to form major subfamilies during early mammalian evolution. Determining how and when the expansion occurred is important as it will help us to understand the various functions that present-time RNase genes.