The Difference Of Antimicrobial Peptides Between The Rana Amurensis And Pelophylax Nigromaculatus And Its Potential Impacts On Population Dispersal

Dispersal is the main mode that species expand their range and diversify genetically. Success dispersal is the consequence of survival and reproduction in new environment. The skin of amphibians is lack of physical barriere and of high transimissivity, placing the amphibians in the challenges of micro-organisms. The major defensive agents are antimicrobial peptides (AMPs) that are function nal in killing bacteria, viruses, parasites and tumor cells. It can be hypothesized that AMPs play important role in dispersal of amphibians to novel micro-organism environment. In order to examine the hypothesis, we carried out a study on the expression profile of AMPs of the Siberian wood frog (Rana amurensis) which dispersed northward from orign center and black spotted frog (Pelophylax nigromaculatus) which dispersed southward using RT-PCR technology. Totally 82 AMP cDNAs were isolated from Siberian wood frog belonging to 14 families,8 families of wich were identified for the first time, and 96 AMP cDNAs were isolated from black spotted frog belonging to 11 familes,6 families of which were identified for the first time, including acidic AMPs (family Nigrocin-3N and Nigrocin-4N). Bioinformative study demonstrated that diversification of AMPs of Siberian wood frog were more significant in profile composition, structure, and chemical & physical properties than that in black spotted frog. This might result in lower extent of overlapping of antimicrobial spectrums of different AMPs in Siberian wood frog, and alteration of certain AMPs by mutations might leave defects on the whole antimicrobial spectrum. Mutations mainly occur on amono acid residues not significantly affecting the charges numbers and polarity of AMPs in black spotted frogs, while mutations in Siberian wood frog usually resulted in alteration of chemical and physical properties. This might make the antimcrobial spectrum more instable in Siberian wood frog. Codon usage of AMPs was affected by both nucleotide composition and selection at translation level in black spotted frogs. In contrast, codon usage was only affected by selection at translation level. In addition, a group of AMPs presented in black spotted frog had very high values of the frequency of nonsynonymous mutations (dN) and the frequency of nonsynonymous mutations (dS) indicating active mutation, but was absent in Siberian wood frog. The results above suggest the AMP system of black spotted frog is stable and of higher potential for accumulating mutations, which enhance the potential of surviving novel and complex micro-organism communities during dispersal southward. In contrast, the AMP system of Siberian wood frog is instable and of lower potential for accumulating mutations, which reduce the potential of surviving novel and complex micro-organism communities during dispersal southward, therefore, this species only dispersed northward. In addition, the range of the two species overlaps in northeast China but AMPs diversify greatly, suggesting a similar micro-organism community can be coped with using different set of AMPs.