Popodi E, Raff R A
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Bioessays. 2001 Mar;23(3):211-4. doi: 10.1002/1521-1878(200103)23:3<211::AID-BIES1030>3.0.CO;2-6.
There is renewed interest in how the different body plans of extant phyla are related. This question has traditionally been addressed by comparisons between vertebrates and Drosophila. Fortunately, there is now increasing emphasis on animals representing other phyla. Pentamerally symmetric echinoderms are a bilaterian metazoan phylum whose members exhibit secondarily derived radial symmetry. Precisely how their radially symmetric body plan originated from a bilaterally symmetric ancestor is unknown, however, two recent papers address this subject. Peterson et al. propose a hypothesis on evolution of the anteroposterior axis in echinoderms, and Arenas-Mena et al. examine expression of five posterior Hox genes during development of the adult sea urchin.
现存的不同门的身体结构是如何关联的，这一问题再次引发了人们的兴趣。传统上，这个问题是通过比较脊椎动物和果蝇来解决的。幸运的是，现在越来越强调以代表其他门的动物为研究对象。五辐射对称的棘皮动物是一种两侧对称的后生动物门，其成员呈现出次生的辐射对称。然而，它们的辐射对称身体结构究竟是如何从两侧对称的祖先演化而来的尚不清楚，不过最近有两篇论文探讨了这个主题。彼得森等人提出了一个关于棘皮动物前后轴进化的假说，阿雷纳斯 - 梅纳等人研究了成年海胆发育过程中五个后Hox基因的表达情况。
