Adaptive Evolutionary Expansion of the Pancreatic ribonuclease 6 (RNase6) in Rodentia.

Pancreatic ribonuclease 6 (RNase6 or RNase K6) is a protein that belongs to a superfamily thought to be the sole vertebrate-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 two 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 have occurred in the Ctenohystrica clade. The diversification of the isoelectric point and positive net charge at the key site Trp30 has undergone positive selection and Ile45 changed into other residues in some duplicate genes, both of which are involved in antimicrobial function. 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. This article is protected by copyright. All rights reserved.