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

Lau, Quintin, Igawa, Takeshi, Kosch, Tiffany, and Satta, Yoko (2018) Selective constraint acting on TLR2 and TLR4 genes of Japanese Rana frogs. PeerJ, 6.

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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.

Item ID: 53977
Item Type: Article (Research - C1)
ISSN: 2167-8359
Keywords: amphibian, Ranidae, toll-like receptors
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This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited.

Funders: Japan Society for Promotion of Science (JSPS), Grant-in-Aid for Scientific Research (KAKENHI)
Projects and Grants: KAKENHI 17K15053
Date Deposited: 26 Jun 2018 02:14
FoR Codes: 31 BIOLOGICAL SCIENCES > 3105 Genetics > 310507 Genetic immunology @ 50%
31 BIOLOGICAL SCIENCES > 3105 Genetics > 310510 Molecular evolution @ 30%
31 BIOLOGICAL SCIENCES > 3105 Genetics > 310505 Gene expression (incl. microarray and other genome-wide approaches) @ 20%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960805 Flora, Fauna and Biodiversity at Regional or Larger Scales @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 50%
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