Hox genes of the direct-type developing sea urchin Peronella japonica

Peronella japonica是一种直接型发育的海胆，在3天内变态，无需喂食，为我们提供了一个很好的系统来分析发育机制，特别是在后期幼虫阶段变态。利用PCR和RT-PCR技术对日本对虾的Hox型基因序列进行了检测，共分离出13个Hox型基因序列。RT-PCR检测结果表明，所有的基因在幼虫中均有表达。系统发育分析和数据库搜索导致鉴定出在其他海胆中已报道的Hox基因的所有日本对虾直系同源物，加上3个Hox型基因：Evx型，Xlox型和一个额外的后Hox基因。本研究结果揭示了一个推定的日本对虾Hox基因簇，它包含了脊椎动物Hox基因簇的所有同源群的基因，除了有一个Hox 4 -5类型的基因。尽管五辐体平面缺乏明显的头部结构，但P. japonica似乎保留了Hox簇，这与具有双侧体平面的脊索动物基本相似。

Peronella japonica is a direct-type developing sea urchin that metamorphoses in 3 days without feeding, providing us a good system to analyze developmental mechanisms especially at later larval stages to metamorphosis. We surveyed the Hox-type sequences of P. japonica by PCR and RT-PCR, and isolated 13 Hox-type sequences. All of them were detected by RT-PCR, indicative of their expressions in larvae. Phylogenetic analysis and database searches resulted in identification of all the P. japonica orthologs of the Hox genes that have been reported in other sea urchins, plus 3 Hox-type genes: the Evx-type, Xlox-type, and an additional posterior Hox gene. The present results revealed a putative Hox gene cluster of P. japonica, which contains genes representing all the paralog (cognate) groups of vertebrate Hox clusters except that there is a single gene of Hox4-5 types. In spite of the pentaradial body plans lacking apparent cepharic structures, P. japonica appears to retain the Hox cluster that is essentially similar to those of the chordates with bilateral body plans.