Schummer M, Scheurlen I, Schaller C, Galliot B
Zentrum für Molekulare Biologie, Heidelberg, FRG.
EMBO J. 1992 May;11(5):1815-23. doi: 10.1002/j.1460-2075.1992.tb05233.x.
Hydra, a diblastic animal consisting of two cell layers, ectoderm and endoderm, is one of the most ancient animals displaying an anteroposterior axis with a head and a foot developing from an uncommitted gastric region. As such, hydra is an interesting model for studying the presence and function of homeobox genes in a phylogenetically old organism. By screening a Chlorohydra viridissima cDNA library with a 'guessmer' oligonucleotide, we have cloned several such cnidarian homeobox-containing genes (cnox genes). Two of these, cnox1 and cnox2, display labial and Deformed type homeodomains respectively and could represent two ancestral genes of the HOM/HOX complexes; cnox3 exhibits some similarity to the BarH1 and the distal-less type homeodomains and a fourth gene is highly related to the msh/Hox7 type of homeodomain. We used quantitative PCR to study levels of expression of these genes along the body axis and during head regeneration. In all cases, the expression in heads was stronger than that in the gastric region. cnox1 transcripts dramatically peaked within the first hours of head regeneration, whereas cnox2 and cnox3 reached their maximal levels 1 and 2 days after cutting respectively. This differential expression of homeobox genes at various stages of regeneration suggests that they play specific roles in regenerative processes.
水螅是一种双胚层动物，由外胚层和内胚层两个细胞层组成，是最古老的动物之一，具有前后轴，头部和足部从未分化的胃区发育而来。因此，水螅是研究系统发育古老生物体中同源框基因的存在和功能的有趣模型。通过用“猜测者”寡核苷酸筛选绿褐水螅cDNA文库，我们克隆了几个这样的含有刺胞动物同源框的基因（cnox基因）。其中两个，cnox1和cnox2，分别显示唇形和变形型同源结构域，可能代表HOM/HOX复合体的两个祖先基因；cnox3与BarH1和远端缺失型同源结构域有一些相似性，第四个基因与msh/Hox7型同源结构域高度相关。我们使用定量PCR研究这些基因在身体轴上以及头部再生过程中的表达水平。在所有情况下，头部的表达都比胃区更强。cnox1转录本在头部再生的最初几个小时内急剧达到峰值，而cnox2和cnox3分别在切割后1天和2天达到最高水平。同源框基因在再生不同阶段的这种差异表达表明它们在再生过程中发挥着特定作用。
