Zink Robert M
School of Natural Resources, School of Biological Sciences, Nebraska State Museum, University of Nebraska-Lincoln, Lincoln, NE 68503, USA.
Heliyon. 2021 Apr 16;7(4):e06801. doi: 10.1016/j.heliyon.2021.e06801. eCollection 2021 Apr.
Evolutionary biologists and disease biologists use the terms strain and adaptation in Chronic Wasting Disease (CWD) research in different ways. In evolutionary biology, a strain is a nascent genetic lineage that can be described by a genealogy, and a phylogenetic nomenclature constructed to reflect that genealogy. Prion strains are described as showing distinct host range, clinical presentation, disease progression, and neuropathological and PrP biochemical profiles, and lack information that would permit phylogenetic reconstruction of their history. Prion strains are alternative protein conformations, sometimes derived from the same genotype. I suggest referring to prion strains as ecotypes, because the variant phenotypic conformations ("strains") are a function of the interaction between PRNP amino acid genotype and the host environment. In the case of CWD, a prion ecotype in white-tailed deer would be described by its genotype and the host in which it occurs, such as the H95 + ecotype. However, an evolutionary nomenclature is difficult because not all individuals with the same PRNP genotype show signs of CWD, therefore creating a nomenclature reflecting and one-to-one relationship between PRNP genealogy and CWD presence is difficult. Furthermore, very little information exists on the phylogenetic distribution of CWD ecotypes in wild deer populations. Adaptation has a clear meaning in evolutionary biology, the differential survival and reproduction of individual genotypes. If a new prion ecotype arises in a particular host and kills more hosts or kills at an earlier age, it is the antithesis of the evolutionary definition of adaptation. However, prion strains might be transmitted across generations epigenetically, but whether this represents adaptation depends on the fitness consequences of the strain. Protein phenotypes of PRNP that cause transmissible spongiform encephalopathies (TSEs), and CWD, are maladaptive and would not be propagated genetically or epigenetically via a process consistent with an evolutionary view of adaptation. I suggest terming the process of prion strain origination "phenotypic transformation", and only adaptation if evidence shows they are not maladaptive and persist over evolutionary time periods (e.g., thousands of generations) and across distinct species boundaries (via inheritance). Thus, prion biologists use strain and adaptation, historically evolutionary terms, in quite different ways.
进化生物学家和疾病生物学家在慢性消耗病（CWD）研究中对“毒株”和“适应性”这两个术语的使用方式不同。在进化生物学中，一个毒株是一个新生的遗传谱系，可以用一个系谱来描述，并构建一个系统发育命名法来反映该系谱。朊病毒毒株被描述为具有不同的宿主范围、临床表现、疾病进展以及神经病理学和PrP生化特征，并且缺乏能够对其历史进行系统发育重建的信息。朊病毒毒株是替代性的蛋白质构象，有时源自相同的基因型。我建议将朊病毒毒株称为生态型，因为变异的表型构象（“毒株”）是PRNP氨基酸基因型与宿主环境之间相互作用的结果。就CWD而言，白尾鹿中的一种朊病毒生态型将通过其基因型和出现该生态型的宿主来描述，例如H95 +生态型。然而，建立一个进化命名法很困难，因为并非所有具有相同PRNP基因型的个体都会出现CWD的症状，因此很难创建一个反映PRNP系谱与CWD存在之间一一对应关系的命名法。此外，关于野生鹿群中CWD生态型的系统发育分布的信息非常少。在进化生物学中，“适应性”有明确的含义，即个体基因型的差异存活和繁殖。如果一种新的朊病毒生态型在特定宿主中出现并杀死更多宿主或在更早的年龄杀死宿主，这与适应性的进化定义相反。然而，朊病毒毒株可能通过表观遗传方式在代际间传播，但这是否代表适应性取决于该毒株对适应性的影响。导致传染性海绵状脑病（TSEs）和CWD的PRNP蛋白质表型是适应不良的，不会通过与适应性的进化观点一致的过程在遗传或表观遗传上传播。我建议将朊病毒毒株起源的过程称为“表型转变”，只有当有证据表明它们不是适应不良的，并且在进化时间段（例如数千代）内持续存在并跨越不同物种边界（通过遗传）时，才称之为适应性。因此，朊病毒生物学家对“毒株”和“适应性”这两个历史上的进化术语的使用方式截然不同。
