Birth-and-death evolution of ribonuclease 9 genes in Cetartiodactyla.

RNase9 plays a reproductive function and has been recognized as an important member of the ribonuclease (RNase) A superfamily, a gene family that is widely used as a model for molecular evolutionary studies. Here, we identified 178 RNase9 genes from 95 Cetartiodactyla species that represent all four lineages and 21 families of this clade. Unexpectedly, RNase9 experienced an evolutionary scenario of "birth and death" in Ruminantia, and expression analyses showed that duplicated RNase9A and RNase9B genes are expressed in reproductive tissues (epididymis, vas deferens or prostate). This expression pattern combined with the estimate that these genes duplicated during the middle Eocene, a time when Ruminantia become a successful lineage, suggests that the RNase9 gene duplication might have been advantageous for promoting sperm motility and male fertility as an adaptation to climate seasonality changes of this period. In contrast, all RNase9 genes were lost in the Cetacean lineage, which might be associated with their high levels of prostatic lesions and lower reproductive rates as adaptations to a fully aquatic environment and a balance to the demands of ocean resources. This study reveals a complex and intriguing evolutionary history and functional divergence for RNase9 in Cetartiodactyla, providing new insights into the evolution of the RNaseA superfamily and molecular mechanisms for organismal adaptations to the environment.

Adaptive evolutionary expansion of the ribonuclease 6 in Rodentia.

Ribonuclease 6 (RNase6 or RNase K6) is a protein that belongs to a superfamily thought to be the sole verte-brate-specific enzyme known for a wide range of physiological functions, including digestion, cytotoxicity, angiogenesis, male reproduction and host defense. In our study, 51 functional genes and 11 pseudogenes were identified from 27 Rodentia species. Intriguingly, in the 3 main lineages of rodents there were multiple RNase6s identified in all species of Ctenohystrica, whereas only a single RNase6 was observed in other Rodentia species examined except for 2 species in the mouse-related clade. The evolutionary scenario of "birth (gene duplication) and death (gene deactivation)" and gene sorting have been demonstrated in Ctenohystrica. In addition, bursts of positive selection, diversification of isoelectric point and positive net charge have been identified in Ctenohystrica, especially at two key sites that are involved in antimicrobial function. Site Trp30 has undergone positive selection and Ile45 has changed into other residues in Group B and Group C of the Ctenohystrica. Our results demonstrated a complex and intriguing evolutionary pattern of rodent RNase6, and indicated that functional modification may have occurred, which establishes an important theoretical foundation for future functional assays in rodent RNase6.

[Molecular evolution of the ribonuclease A superfamily].

Ribonuclease A (RNASE A) superfamily is one of the model systems for studying new gene origin and functional innovations in evolutionary biology. Remarkably, gene duplications have been found in many members of RNASE A superfamily, and the functional differentiations of the duplicated genes have been demonstrated to be driven by the adaptive (positive) selection. In this review, we summarize the researches on the evolutionary patterns of RNASE A genes in differ-ent species, especially the recent researches at the genomic levels, suggesting a far more complex and intriguing evolution-ary diversity of RNASE A than previously thought. In the future, along with the increasing numbers of animal genomes available, the studies of RNASE A from more species are expected to reveal new evolutionary patterns and functional di-versifications, which will lay a foundation for the systematic studies on the molecular basis of adaptive evolution.