Molecular Evolution Of RNase4 Gene In Chiroptera

The RNase A superfamily is a vertebrate-specific enzyme family which has serve as important model for the molecular evolution studies. Gene duplication and pseudogenization events show difference in different organisms for the special member, which is strongly linked with the functional differentiation. Goo et al’s analysis of the RNase A superfamily members for mammalian, a single RNase4 gene was identified in Pteropus vampyrus, which is the representative species of the Pteropodiae of the Yinpterochiropotera suborder. On the contrary,12 RNase4 genes were detected in Myotis lucifugus, which represent the Vespertilionidae of the Yangochiroptera. This fascinating result indicates that RNase4 have a specific evolution pattern and functional differentiation in Chiroptera. More species of Chiroptera are needed to investigate in which the gene duplication occurred, the time and the evolutionary force of gene duplication. In order to figure out that the time, mechanism and whether the gene duplication event had been occurred in other species, more samples of Chiroptera will be needed.In this study,9 families covering 25 genus,28 species of the five superfamilies (Pteropodidae, Rhinolophidea, Embollonuridea, Noctilionoidea and Vespertiliondea) of the two suborder (Yinterochiroptera and Yangochiroptera) in Chiroptera were used for the molecular evolution study of RNase4. The results show that the gene duplication of RNase4 is occurred only in the Vespertiliondae. The other species only have one function gene except for the Pteropus alecto, which have only one pseudogene. The pseudogenization of RNase4 in the Pteropus alecto suggests that it is non-functional. Phylogenetic result indicates that a gene duplication event and a psudogenization event, one after another, occurred in the ancestor of Vespertiliondae. Numbers of gene duplications, which occurred prior to the origin of this species according to the divergence time estimate are identified in the Myotis of Vespertiliondae, at least twice, and resulted in gene cluster patterns. This suggest that the adaptive evolution of the function of host defense. Moreover, the gene duplication in the Scotophilus is a recent event posterior to speciation.A total of 14 positive sites have been detected in the analysis of site-specific model. The site Q76E and Q98K are close to the active region, indicating that both mutants may change the function of RNase4 by affecting the substrate-enzyme model. In the other hand, significant positive selection signals are detected by the analysis of branch-site model in Chiropetera, implying that there are two positive sites in cluster B. All the above results suggest that adaptive selection may had driven the gene duplication, and potential function differentiation of RNase4 in Chiroptera.To sum up, this study revealde specific evolution pattern of RNase4 by investigating specifies in Chiroptera, which is crucial for further studies of the function of RNase4.