Dai Zhonghua, Chen Zuozhou, Ye Hua, Zhou Longhai, Cao Lixue, Wang Yiquan, Peng Sihua, Chen Liangbiao
Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Evol Dev. 2009 Jan-Feb;11(1):41-9. doi: 10.1111/j.1525-142X.2008.00301.x.
Cephalochordates, urochordates, and vertebrates comprise the three extant groups of chordates. Although higher morphological and developmental similarity exists between cephalochordates and vertebrates, molecular phylogeny studies have instead suggested that the morphologically simplified urochordates are the closest relatives to vertebrates. MicroRNAs (miRNAs) are regarded as the major factors driving the increase of morphological complexity in early vertebrate evolution, and are extensively characterized in vertebrates and in a few species of urochordates. However, the comprehensive set of miRNAs in the basal chordates, namely the cephalochordates, remains undetermined. Through extensive sequencing of a small RNA library and genomic homology searches, we characterized 100 miRNAs from the cephalochordate amphioxus, Branchiostoma japonicum, and B. floridae. Analysis of the evolutionary history of the cephalochordate miRNAs showed that cephalochordates possess 54 miRNA families homologous to those of vertebrates, which is threefold higher than those shared between urochordates and vertebrates. The miRNA contents demonstrated a clear correlation between the extent of miRNA overlapping and morphological similarity among the three chordate groups, providing a strong evidence of miRNAs being the major genetic factors driving morphological complexity in early chordate evolution.
头索动物、尾索动物和脊椎动物构成了现存的三类脊索动物。尽管头索动物和脊椎动物之间存在更高的形态学和发育相似性，但分子系统发育研究反而表明，形态简化的尾索动物是脊椎动物最亲近的亲属。微小RNA（miRNA）被认为是早期脊椎动物进化过程中推动形态复杂性增加的主要因素，并且在脊椎动物和少数几种尾索动物中得到了广泛的表征。然而，基础脊索动物，即头索动物中的miRNA完整集合仍未确定。通过对一个小RNA文库进行广泛测序和基因组同源性搜索，我们从日本文昌鱼（Branchiostoma japonicum）和佛罗里达文昌鱼（B. floridae）这两种头索动物中鉴定出了100种miRNA。对头索动物miRNA进化历史的分析表明，头索动物拥有54个与脊椎动物同源的miRNA家族，这比尾索动物和脊椎动物之间共享的家族数量高出三倍。miRNA含量表明，这三类脊索动物之间miRNA重叠程度与形态相似性之间存在明显的相关性，为miRNA是早期脊索动物进化过程中推动形态复杂性的主要遗传因素提供了有力证据。
