絶滅の危機に瀕したシカの致命的な病気の脅威を回避する遺伝子の多様性(How genetic diversity could avoid threat of deadly disease in endangered deer)

2022-10-12

2022-10-11 イリノイ大学アーバナ・シャンペーン校

オジロジカなどのシカ科動物を侵すプリオン病である慢性消耗病が拡大している。米国29州、カナダ2州、北欧3カ国、韓国で感染が確認され、放し飼いにされているシカや飼育されているシカは脅威にさらされている。このような背景から、絶滅の危機に瀕したシカを保護するための努力は、当然のことながら困難なものとなっている。
米国の動物園から採取した36頭のエルド鹿で、別の遺伝子変異を同定した。この遺伝子変異は、集団の中ではあまり一般的ではなかったが、ペール・ダヴィッド種のシカの遺伝子変異と同じものであった。他の種の研究によれば、この遺伝子変異は、適切に管理されれば、エルドとペールダビデのシカにCWD(慢性消耗病)に対する抵抗力を与える可能性があるとのことである。

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プリオンタンパク質遺伝子(PRNP)多型から見たエルド鹿(Rucervus eldii thamin)の慢性消耗病感受性の外挿性
Extrapolating the susceptibility of Eld’s deer (Rucervus eldii thamin) to chronic wasting disease from prion protein gene (PRNP) polymorphisms

Tolulope I.N. Perrin-Stowe, Yasuko Ishida, Dolores M. Reed, Emily E. Terrill, Oliver A. Ryder, Jan E. Novakofski, Nohra E. Mateus-Pinilla, Budhan S. Pukazhenthi and Alfred L. Roca
Frontiers in Conservation Science Published:11 October 2022
DOI:https://doi.org/10.3389/fcosc.2022.1007100

Chronic wasting disease (CWD) is a prion disease of North American cervids. The transmission of CWD to endangered cervid species is of concern for captive breeding programs. Trans-species transmission could occur via direct contact with infected wild deer, or via prion contaminated fomites. Variation in the prion protein gene, PRNP, is associated with differences in CWD susceptibility among cervids. We therefore sequenced PRNP in 36 endangered Eld’s deer (Rucervus eldii thamin), detecting five synonymous and two non-synonymous SNPs. Three haplotypes were inferred, suggesting that genetic management in captive breeding programs has been effective at maintaining PRNP diversity. The haplotypes encoded two PrP protein variants. The more common Eld’s deer PrP variant encodes methionine at codon 208 and glutamine at codon 226. Because this protein variant is identical to a common PrP variant in white-tailed deer and mule deer and is especially common in white-tailed deer positive for CWD, we recommend reducing the frequency of this variant in the breeding stock, while implementing strict management practices to avoid exposure to wild North American cervids. The frequency of the other PrP variant, which differs from variants present in these North American cervids, was low. It has the potential to reduce susceptibility to CWD and thus could be increased in frequency. While PRNP haplotype frequencies should be shifted, genetic diversity should be maintained. Ultimately protein diversity may be protective should CWD infect the species, and trans-species polymorphisms are suggestive of past balancing selection and a potential fitness advantage for PRNP diversity.