Layeghifard Mehdi, Rabani Razieh, Pirhaji Leila, Yakhchali Bagher
Department des Sciences Biologiques, Université du Québec à Montréal (UQAM), CP 8888, Succ. Centre Ville, Montréal, QC, Canada H3C 3P8.
Gene. 2008 Dec 15;426(1-2):65-71. doi: 10.1016/j.gene.2008.08.014. Epub 2008 Sep 3.
Circadian rhythms, that are governed physiologically and behaviorally by endogenous clock, have been described in many species. Living organisms use this endogenous circadian clock to anticipate environmental transitions, perform activities at biologically advantageous times during the day, and undergo characteristic seasonal responses. Gene duplication is one of the most important mechanisms in the evolution of gene diversity. After duplication, one or both of duplicates can accumulate amino acid changes, thereby promoting functional divergence through the action of natural selection. The circadian system, like many other multigene families, has undergone this genetic revolution, and so circadian genes that are found in single copies in insects are duplicated in vertebrates. We analyzed six groups of genes involved in vertebrates' circadian rhythm pathway to find signatures of molecular evolutionary processes such as gene duplication, natural selection, recombination, and functional divergence. The obtained results, then, were used to determine what evolutionary forces have influenced the fates of duplicated genes of each group. We showed in this research that recombination has not been widespread during the evolution of circadian genes and that purifying selection has been the prominent natural pressure operating on circadian genes. We also showed that the evolution of circadian genes has been depended on gene duplication and functional divergence. Finally, we put forward models best describing the evolutionary fates of circadian duplicates.
昼夜节律受内源性生物钟在生理和行为上的调控，在许多物种中都有描述。生物体利用这种内源性昼夜节律生物钟来预测环境变化，在一天中具有生物学优势的时间进行活动，并经历特征性的季节性反应。基因复制是基因多样性进化中最重要的机制之一。复制后，一个或两个复制品都可以积累氨基酸变化，从而通过自然选择的作用促进功能分化。与许多其他多基因家族一样，昼夜节律系统也经历了这种基因革命，因此在昆虫中以单拷贝形式存在的昼夜节律基因在脊椎动物中是重复的。我们分析了参与脊椎动物昼夜节律途径的六组基因，以寻找分子进化过程的特征，如基因复制、自然选择、重组和功能分化。然后，将获得的结果用于确定哪些进化力量影响了每组重复基因的命运。我们在这项研究中表明，在昼夜节律基因的进化过程中，重组并不普遍，纯化选择是作用于昼夜节律基因的主要自然压力。我们还表明，昼夜节律基因的进化依赖于基因复制和功能分化。最后，我们提出了最能描述昼夜节律复制品进化命运的模型。
