Cook Charles E, Jiménez Eva, Akam Michael, Saló Emili
University Museum of Zoology, Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK.
Evol Dev. 2004 May-Jun;6(3):154-63. doi: 10.1111/j.1525-142X.2004.04020.x.
Several molecular data sets suggest that acoelomorph flatworms are not members of the phylum Platyhelminthes but form a separate branch of the Metazoa that diverged from all other bilaterian animals before the separation of protostomes and deuterostomes. Here we examine the Hox gene complement of the acoel flatworms. In two distantly related acoel taxa, we identify only three distinct classes of Hox gene: an anterior gene, a posterior gene, and a central class gene most similar to genes of Hox classes 4 and 5 in other Bilateria. Phylogenetic analysis of these genes, together with the acoel caudal homologue, supports the basal position of the acoels. The similar gene sets found in two distantly related acoels suggest that this reduced gene complement may be ancestral in the acoels and that the acoels may have diverged from other bilaterians before elaboration of the 8- to 10-gene Hox cluster that characterizes most bilaterians.
多个分子数据集表明，无肠扁形虫并非扁形动物门的成员，而是后生动物中一个独立的分支，它在原口动物和后口动物分化之前就与所有其他两侧对称动物分道扬镳了。在此，我们研究了无肠扁形虫的Hox基因组成。在两个亲缘关系较远的无肠类群中，我们仅识别出三类不同的Hox基因：一个前部基因、一个后部基因，以及一个与其他两侧对称动物中Hox基因家族4和5的基因最为相似的中央类基因。对这些基因以及无肠类尾同源物进行系统发育分析，支持了无肠类的基部位置。在两个亲缘关系较远的无肠类中发现的相似基因集表明，这种简化的基因组成可能是无肠类的祖先特征，并且无肠类可能在大多数两侧对称动物所特有的8到10个基因的Hox簇形成之前就与其他两侧对称动物分化了。
