Akam M
Wellcome/CRC Institute and Department of Genetics, Cambridge, U.K.
Philos Trans R Soc Lond B Biol Sci. 1995 Sep 29;349(1329):313-9. doi: 10.1098/rstb.1995.0119.
Homeobox genes encode transcription factors that carry out diverse roles during development. They are widely distributed among eukaryotes, but appear to have undergone an extensive radiation in the earliest metazoa, to generate a range of homeobox subclasses now shared between diverse metazoan phyla. The Hox genes comprise one of these subfamilies, defined as much by conserved chromosomal organization and expression as by sequence characteristics. These Hox genes act as markers of position along the antero-posterior axis of the body in nematodes, arthropods, chordates, and by implication, most other triploblastic phyla. In the arthropods this role is visualized most clearly in the control of segment identity. Exactly how Hox genes control the structure of segments is not yet understood, but their differential deployment between segments provides a model for the basis of segment diversity. Within the arthropods, distantly related taxonomic groups with very different body plans (insects, crustaceans) may share the same set of Hox genes. The expression of these Hox genes provides a new character to define the homology of different body regions. Comparisons of Hox gene deployment between insects and a branchiopod crustacean suggest a novel model for the derivation of the insect body plan.
同源异型基因编码在发育过程中发挥多种作用的转录因子。它们广泛分布于真核生物中，但似乎在最早的后生动物中经历了广泛的辐射，从而产生了一系列现在不同后生动物门共有的同源异型盒子亚类。Hox基因是这些亚家族之一，其定义不仅基于保守的染色体组织和表达，还基于序列特征。在 nematodes、节肢动物、脊索动物以及大多数其他三胚层门中，这些Hox基因作为沿身体前后轴的位置标记。在节肢动物中，这一作用在体节特征的控制中最为明显。Hox基因究竟如何控制体节结构尚不清楚，但它们在不同体节之间的差异部署为体节多样性的基础提供了一个模型。在节肢动物中，具有非常不同身体结构的远缘分类群（昆虫、甲壳类动物）可能共享同一组Hox基因。这些Hox基因的表达为定义不同身体区域的同源性提供了一个新特征。昆虫和鳃足类甲壳动物之间Hox基因部署的比较为昆虫身体结构的推导提出了一个新模型。
