Arenas-Mena C, Cameron A R, Davidson E H
Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
Development. 2000 Nov;127(21):4631-43. doi: 10.1242/dev.127.21.4631.
The Hox cluster of the sea urchin Strongylocentrous purpuratus contains ten genes in a 500 kb span of the genome. Only two of these genes are expressed during embryogenesis, while all of eight genes tested are expressed during development of the adult body plan in the larval stage. We report the spatial expression during larval development of the five 'posterior' genes of the cluster: SpHox7, SpHox8, SpHox9/10, SpHox11/13a and SpHox11/13b. The five genes exhibit a dynamic, largely mesodermal program of expression. Only SpHox7 displays extensive expression within the pentameral rudiment itself. A spatially sequential and colinear arrangement of expression domains is found in the somatocoels, the paired posterior mesodermal structures that will become the adult perivisceral coeloms. No such sequential expression pattern is observed in endodermal, epidermal or neural tissues of either the larva or the presumptive juvenile sea urchin. The spatial expression patterns of the Hox genes illuminate the evolutionary process by which the pentameral echinoderm body plan emerged from a bilateral ancestor.
紫海胆（Strongylocentrous purpuratus）的Hox基因簇在基因组500 kb的范围内包含10个基因。在胚胎发生过程中，这些基因中只有两个表达，而在幼虫阶段成体体型发育过程中，所检测的8个基因全部表达。我们报告了该基因簇中5个“后位”基因在幼虫发育过程中的空间表达情况：SpHox7、SpHox8、SpHox9/10、SpHox11/13a和SpHox11/13b。这5个基因表现出动态的、主要在中胚层的表达模式。只有SpHox7在五辐幼虫原基本身内有广泛表达。在体腔（成对的后中胚层结构，将发育为成体的围脏腔）中发现了表达域的空间顺序和共线性排列。在幼虫或假定的幼体海胆的内胚层、表皮或神经组织中未观察到这种顺序表达模式。Hox基因的空间表达模式揭示了五辐棘皮动物体型从双侧祖先演化而来的进化过程。
