Sharman A C, Holland P W
School of Animal and Microbial Sciences, The University of Reading, United Kingdom.
Int J Dev Biol. 1998 May;42(4):617-20.
Hox gene clusters are linked arrays of related homeobox genes with important roles in patterning the main body axis of animal embryos. Almost all invertebrates analyzed in detail, including a cephalochordate, have a single Hox gene cluster. In contrast, mammals have four such clusters inferred to have arisen by duplication. Data from other jawed vertebrates, including teleost fish, suggest they have at least four Hox gene clusters, implying that cluster duplication dates to very early in vertebrate evolution. Lampreys descended from one of the earliest vertebrate lineages and are thus critical in dating the duplication events. Here we analyze the Hox gene complement of a freshwater lamprey, Lampetra, using degenerate PCR. By analysis of the DNA sequences, deduced protein sequences, and by comparison to previous data from the distantly related sea lamprey, we conclude that lampreys have approximately 21 Hox genes from paralogous groups 1-10, plus a group 13 Hox gene. The data support the presence of three Hox gene clusters in lampreys more strongly than they support the presence of one, two or four gene clusters. We discuss how this situation may have arisen in evolution.
Hox基因簇是相关同源框基因的连锁阵列，在动物胚胎的主体轴模式形成中发挥重要作用。几乎所有经过详细分析的无脊椎动物，包括一种头索动物，都只有一个Hox基因簇。相比之下，哺乳动物有四个这样的基因簇，推测是通过复制产生的。来自其他有颌脊椎动物的数据，包括硬骨鱼，表明它们至少有四个Hox基因簇，这意味着基因簇复制可追溯到脊椎动物进化的早期。七鳃鳗是最早的脊椎动物谱系之一的后代，因此对于确定复制事件的时间至关重要。在这里，我们使用简并PCR分析了一种淡水七鳃鳗——七鳃鳗属的Hox基因组成。通过对DNA序列、推导的蛋白质序列进行分析，并与来自远缘的海七鳃鳗的先前数据进行比较，我们得出结论，七鳃鳗大约有来自旁系同源群1-10的21个Hox基因，外加一个13群Hox基因。这些数据比支持一个、两个或四个基因簇的存在更有力地支持七鳃鳗中存在三个Hox基因簇。我们讨论了这种情况在进化中可能是如何出现的。
