MicroRNAs （miRNAs） are endogenous -22 nucleotide noncoding RNAs that regulate the expression of complementary messenger RNAs （mRNAs）. Thousands of miRNA genes have been found in diverse species, and many of them are highly conserved. With the miRNA roles identified in nearly all aspects of biological processes, evidence is mounting that miRNAs could represent a new layer of regulatory network, and their regulatory effect might be much more pervasive than previously suspected. Here we focus on the posttranscriptional level gene regulation of miRNAs in animals and review how the miRNAs act to sustain and shape up the expression profiles of specific cell types; how the miRNAs integrate into the existing gene regulatory networks; and how the miRNAs influence the evolution of 3＇UTR of mammalian mRNAs.
To understand the genetic basis that underlies the phenotypic divergence between human and non- human primates, we screened a total of 7176 protein-coding genes expressed in the human brain and compared them with the chimpanzee orthologs to identify genes that show evidence of rapid evolution in the human lineage. Our results showed that the nonsynonymous/synonymous substitution (Ka/Ks) ratio for genes expressed in the brain of human and chimpanzee is 0.3854, suggesting that the brain-expressed genes are under functional constraint. The X-linked human brain-expressed genes evolved more rapidly than autosomal ones. We further dissected the molecular evolutionary patterns of 34 candidate genes by sequencing representative primate species to identify lineage-specific adaptive evolution. Fifteen out of the 34 candidate genes showed evidence of positive Darwinian selection in human and/or chimpanzee lineages. These genes are predicted to play diverse functional roles in em- bryonic development, spermatogenesis and male fertility, signal transduction, sensory nociception, and neural function. This study together with others demonstrated the usefulness and power of phy- logenetic comparison of multiple closely related species in detecting lineage-specific adaptive evolu- tion, and the identification of the positively selected brain-expressed genes may add new knowledge to the understanding of molecular mechanism of human origin.
QI XueBinYANG SuZHENG HongKunWANG YinQiuLIAO ChengHongLIU YingCHEN XiaoHuaSHI HongYU xiaoJingAlice A. LINLuca L. CAVALLI-SFORZAWANG JunSU Bing
