Selective constraint acting on TLR2 and TLR4 genes of Japanese Rana frogs

PeerJ

article

Quintin Lau¹  Takeshi Igawa²  Tiffany A. Kosch³  Yoko Satta¹ 

[1]Department of Evolutionary Studies of Biosystems, Sokendai ,(Graduate University for Advanced Studies)

[2]Amphibian Research Center, Hiroshima University

[3]One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University of North Queensland

关键词: Amphibian;    Ranidae;    Toll-like receptors;   

DOI  :  10.7717/peerj.4842

学科分类：社会科学、人文和艺术（综合）

来源: Inra

【 摘 要 】

Toll-like receptors (TLRs) are an important component of innate immunity, the first line of pathogen defence. One of the major roles of TLRs includes recognition of pathogen-associated molecular patterns. Amphibians are currently facing population declines and even extinction due to chytridiomycosis caused by the Batrachochytrium dendrobatidis (Bd) fungus. Evidence from other vertebrates shows that TLR2 and TLR4 are involved in innate immunity against various fungi. Such genes therefore may play a functional role in amphibian-chytridiomycosis dynamics. Frogs from East Asia appear to be tolerant to Bd, so we examined the genetic diversity that underlies TLR2 and TLR4 from three Japanese Ranidae frog species, Rana japonica, R. ornativentris and R. tagoi tagoi (n = 5 per species). We isolated 27 TLR2 and 20 TLR4 alleles and found that these genes are evolutionarily conserved, with overall evidence supporting purifying selection. In contrast, site-by-site analysis of selection identified several specific codon sites under positive selection, some of which were located in the variable leucine rich repeat domains. In addition, preliminary expression levels of TLR2 and TLR4 from transcriptome data showed overall low expression. Although it remains unclear whether infectious pathogens are a selective force acting on TLRs of Japanese frogs, our results support that certain sites in TLRs of these species may have experienced pathogen-mediated selection.

【 授权许可】

CC BY