Sundin O, Eichele G
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030.
Development. 1992 Apr;114(4):841-52. doi: 10.1242/dev.114.4.841.
Chick Ghox 2.9 protein, a homeodomain-containing polypeptide, is first detected in the mid-gastrula stage embryo and its levels increase rapidly in the late gastrula. At this time, the initially narrow band of expression along the primitive streak expands laterally to form a shield-like domain that encompasses almost the entire posterior region of the embryo and extends anteriorly as far as Hensen's node. We have found that this expression domain co-localizes with a morphological feature that consists of a stratum of refractile, thickened mesoderm. Antibody-staining indicates that Ghox 2.9 protein is present in all cells of this mesodermal region. In contrast, expression within the ectoderm overlying the region of refractile mesoderm varies considerably. The highest levels of expression are found in ectoderm near the streak and surrounding Hensen's node, regions that recent fate mapping studies suggest that primarily destined to give rise to neurectoderm. At the definitive streak stage (Hamburger and Hamilton stage 4) the chick embryo is especially sensitive to the induction of axial malformations by retinoic acid. Four hours after the treatment of definitive streak embryos with a pulse of retinoic acid the expression of Ghox 2.9 protein is greatly elevated. This ectopic expression occurs in tissues anterior to Hensen's node, including floor plate, notochord, presumptive neural plate and lateral plate mesoderm, but does not occur in the anteriormost region of the embryo. The ectopic induction of Ghox 2.9 is strongest in ectoderm, and weaker in the underlying mesoderm. Endoderm throughout the embryo is unresponsive. At stage 11, Ghox 2.9 is normally expressed at high levels within rhombomere 4 of the developing hindbrain. In retinoic-acid-treated embryos which have developed to this stage, typical rhombomere boundaries are largely absent. Nevertheless, Ghox 2.9 is still expressed as a discrete band, but one that is widened and displaced to a more anterior position.
鸡的Ghox 2.9蛋白是一种含同源结构域的多肽，最早在原肠胚中期胚胎中被检测到，其水平在原肠胚后期迅速升高。此时，沿着原条最初狭窄的表达带横向扩展，形成一个盾状结构域，几乎覆盖胚胎的整个后部区域，并向前延伸至亨氏结。我们发现这个表达结构域与一个形态学特征共定位，该形态学特征由一层折射性增厚的中胚层组成。抗体染色表明Ghox 2.9蛋白存在于这个中胚层区域的所有细胞中。相比之下，覆盖折射性中胚层区域的外胚层内的表达差异很大。在靠近原条和围绕亨氏结的外胚层中发现了最高水平的表达，最近的命运图谱研究表明，这些区域主要注定会产生神经外胚层。在明确原条阶段（汉堡和汉密尔顿第4阶段），鸡胚胎对维甲酸诱导的轴向畸形特别敏感。用维甲酸脉冲处理明确原条胚胎4小时后，Ghox 2.9蛋白的表达大大升高。这种异位表达发生在亨氏结前方的组织中，包括底板、脊索、假定的神经板和侧板中胚层，但在胚胎的最前端区域不发生。Ghox 2.9的异位诱导在外胚层中最强，在下面的中胚层中较弱。整个胚胎的内胚层无反应。在第11阶段，Ghox 2.9通常在发育中的后脑菱脑节4内高水平表达。在发育到这个阶段的维甲酸处理的胚胎中，典型的菱脑节边界基本不存在。然而，Ghox 2.9仍然作为一条离散的带表达，但这条带变宽并移位到更靠前的位置。
