Hoshiyama D, Suga H, Iwabe N, Koyanagi M, Nikoh N, Kuma K, Matsuda F, Honjo T, Miyata T
Department of Biophysics, Kyoto University Graduate School of Science, Kyoto 606-8502, Japan.
J Mol Evol. 1998 Dec;47(6):640-8. doi: 10.1007/pl00006421.
Members of the Pax gene family encode transcription factors containing a DNA-binding paired domain which is involved in developmental control and the formation of the central nervous system (CNS). The family members are classified into six classes or subfamilies, depending on the presence or absence of paired-type homeobox and octapeptide. To obtain rough estimates of times when the different classes of the Pax family diverged by gene duplication, we cloned and sequenced a Pax-related cDNA, sPax-2/5/8, from Ephydatia fluviatilis, a freshwater sponge, which encodes a paired-type homeobox and an octapeptide, in addition to a paired domain. A phylogenetic tree based on the paired domain sequences suggest that sPax-2/5/8 is a homologue of vertebrate Pax-2/5/8. It was also suggested that the majority of gene duplications that gave rise to distinct classes has been completed in the very early evolution of animals before the parazoan-eumetazoan split. Long after the ancient gene duplications, further gene duplications that gave rise to members in each subfamily occurred on the chordate lineages and completed before the fish-tetrapod split. This suggests that the major classes of the Pax genes involved in the formation of CNS characteristic of triploblasts had already existed long before the Cambrian explosion of triploblasts, and there is no direct link between the creation of new genes with novel functions and the Cambrian explosion. The pattern of gene diversification found in the Pax family is similar to those in five gene families involved in the signal transduction analyzed by us. Furthermore, the evolutionary rates of the Pax proteins have been shown to decrease with increasing organismal complexity during animal evolution.
Pax基因家族的成员编码含有DNA结合配对结构域的转录因子，该结构域参与发育控制和中枢神经系统（CNS）的形成。根据是否存在配对型同源框和八肽，该家族成员被分为六个类别或亚家族。为了大致估计不同类别的Pax家族通过基因复制发生分化的时间，我们从淡水海绵弗氏埃氏海绵（Ephydatia fluviatilis）中克隆并测序了一个与Pax相关的cDNA，即sPax-2/5/8，它除了编码一个配对结构域外，还编码一个配对型同源框和一个八肽。基于配对结构域序列构建的系统发育树表明，sPax-2/5/8是脊椎动物Pax-2/5/8的同源物。研究还表明，导致不同类别的大多数基因复制在动物非常早期的进化过程中就已完成，发生在侧生动物 - 真后生动物分化之前。在古老的基因复制很久之后，导致每个亚家族成员产生的进一步基因复制发生在脊索动物谱系上，并在鱼类 - 四足动物分化之前完成。这表明参与三胚层动物中枢神经系统形成的主要Pax基因类别早在三胚层动物寒武纪大爆发之前就已存在，并且具有新功能的新基因的产生与寒武纪大爆发之间没有直接联系。在Pax家族中发现的基因多样化模式与我们分析的参与信号转导的五个基因家族中的模式相似。此外，在动物进化过程中，Pax蛋白的进化速率已被证明随着生物体复杂性的增加而降低。
