Whitacre James M, Lin Joseph, Harding Angus
Computer Science, University of Birmingham Birmingham, UK.
Front Genet. 2012 Feb 9;3:5. doi: 10.3389/fgene.2012.00005. eCollection 2012.
Evolution is often characterized as a process involving incremental genetic changes that are slowly discovered and fixed in a population through genetic drift and selection. However, a growing body of evidence is finding that changes in the environment frequently induce adaptations that are much too rapid to occur by an incremental genetic search process. Rapid evolution is hypothesized to be facilitated by mutations present within the population that are silent or "cryptic" within the first environment but are co-opted or "exapted" to the new environment, providing a selective advantage once revealed. Although cryptic mutations have recently been shown to facilitate evolution in RNA enzymes, their role in the evolution of complex phenotypes has not been proven. In support of this wider role, this paper describes an unambiguous relationship between cryptic genetic variation and complex phenotypic responses within the immune system. By reviewing the biology of the adaptive immune system through the lens of evolution, we show that T cell adaptive immunity constitutes an exemplary model system where cryptic alleles drive rapid adaptation of complex traits. In naive T cells, normally cryptic differences in T cell receptor reveal diversity in activation responses when the cellular population is presented with a novel environment during infection. We summarize how the adaptive immune response presents a well studied and appropriate experimental system that can be used to confirm and expand upon theoretical evolutionary models describing how seemingly small and innocuous mutations can drive rapid cellular evolution.
进化通常被描述为一个涉及渐进性基因变化的过程，这些变化通过基因漂变和选择在种群中缓慢地被发现并固定下来。然而，越来越多的证据表明，环境变化常常会引发适应性变化，而这些变化发生得太快，不可能通过渐进性基因搜索过程来实现。快速进化被假定是由种群中存在的突变所推动的，这些突变在第一种环境中是沉默的或“隐蔽的”，但在新环境中被选用或“扩展适应”，一旦显现便提供了一种选择优势。尽管最近已证明隐蔽突变有助于RNA酶的进化，但其在复杂表型进化中的作用尚未得到证实。为支持这一更广泛的作用，本文描述了免疫系统内隐蔽遗传变异与复杂表型反应之间的明确关系。通过从进化的角度审视适应性免疫系统的生物学特性，我们表明T细胞适应性免疫构成了一个典范模型系统，其中隐蔽等位基因驱动复杂性状的快速适应。在初始T细胞中，当细胞群体在感染期间面对新环境时，T细胞受体中通常隐蔽的差异会揭示激活反应的多样性。我们总结了适应性免疫反应如何呈现出一个经过充分研究且合适的实验系统，可用于证实和扩展描述看似微小且无害的突变如何驱动快速细胞进化的理论进化模型。
