microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate

Hagfish and lampreys are the only living representatives of the jawless vertebrates (agnathans), and compared with jawed vertebrates (gnathostomes), they provide insight into the embryology, genomics, and body plan of the ancestral vertebrate. However, this insight has been obscured by controversy over their interrelationships. Morphological cladistic analyses have identified lampreys and gnathostomes as closest relatives, whereas molecular phylogenetic studies recover a monophyletic Cyclostomata (hagfish and lampreys as closest relatives). Here, we show through deep sequencing of small RNA libraries, coupled with genomic surveys, that Cyclostomata is monophyletic: hagfish and lampreys share 4 unique microRNA families, 15 unique paralogues of more primitive microRNA families, and 22 unique substitutions to the mature gene products. Reanalysis of morphological data reveals that support for cyclostome paraphyly was based largely on incorrect character coding, and a revised dataset is not ...

盲鳗与七鳃鳗是现存仅存的无颌脊椎动物（agnathans）类群，相较于有颌脊椎动物（gnathostomes），它们为解析脊椎动物祖先的胚胎学、基因组学特征与躯体构型提供了关键视角。然而，关于二者演化相互关系的争议，却一度使得这类研究视角变得模糊不清。形态学分支分类分析曾将七鳃鳗与有颌脊椎动物认定为最近缘类群，而分子系统发育研究则支持单系圆口类（Cyclostomata）假说，即盲鳗与七鳃鳗互为最近缘类群。本研究通过小RNA文库深度测序结合基因组筛查证实，圆口类确为单系群：盲鳗与七鳃鳗共享4个独特的微小RNA（microRNA）家族、15个源自更原始微小RNA家族的独特旁系同源拷贝，以及22个成熟基因产物特有的碱基替换。对形态学数据的重新分析显示，此前支持圆口类并系群的结论，主要基于错误的性状编码，而修正后的数据集暂未……