Evolution under canalization and the dual roles of microRNAs—A hypothesis

Chung-I Wu; Yang Shen; Tian Tang

doi:10.1101/gr.084640.108

Evolution under canalization and the dual roles of microRNAs—A hypothesis

¹ Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA;
² State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen (Zhongshan) University, Guangzhou 510275, People's Republic of China;
³ Beijing Genomics Institute, Chinese Academy of Sciences, Beijing 101300, China

Abstract

Canalization refers to the process by which phenotypes are stabilized within species. Evolution by natural selection can proceed efficiently only when phenotypes are canalized. The existence and identity of canalizing genes have thus been an important, but controversial topic. Recent evidence has increasingly hinted that microRNAs may be involved in canalizing gene expression. Their paradoxical properties (e.g., strongly conserved but functionally dispensable) suggest unconventional regulatory roles. We synthesized published and unpublished results and hypothesize that miRNAs may have dual functions—in gene expression tuning and in expression buffering. In tuning, miRNAs modify the mean expression level of their targets, but in buffering they merely reduce the variance around a preset mean. In light of the constant emergence of new miRNAs, we further discuss the relative importance of these two functions in evolution.