Stein S, Kessel M
Max-Planck-Institut für biophysikalische Chemie, Abteilung Molekulare Zellbiologie, Göttingen, Germany.
Mech Dev. 1995 Jan;49(1-2):37-48. doi: 10.1016/0925-4773(94)00300-c.
We have isolated a chicken cDNA clone, Cnot, resembling in sequence and expression pattern the Xenopus homeobox gene Xnot. The major, early transcription domains of Cnot are the node, the notochord and prenodal and postnodal neural plate caudal from the prospective hindbrain level. All these cell populations appear to be descendants of the Cnot-expressing cells of the node, suggesting a cell lineage relationship. After the onset of somitogenesis, a second, independent expression domain appears in the neural folds at the prospective mid- and forebrain levels, and further transcripts are found in the epiphysis, the ventral diencephalon, the preoral gut and the limb buds. Transplantation of nodes from extended streak embryos leads to the formation of ectopic notochords, which express Cnot in the typical, cranially decreasing gradient. Transplantation of young nodes to young hosts has previously been described to induce secondary embryos. We observed that secondary chick embryos express Cnot in node derived, notochord-like structures and in the anterior neural plate, similar to the domains seen in primary embryos. However, expression was absent from the posterior neural plate, which in the induction experiments is excluded from the node lineage. This finding corroborates our initial conclusion about a cell lineage relationship between node, notochord, and neural plate defined by Cnot expression. The midline mesoderm of vertebrate embryos consists of two tissues, the prechordal mesoderm and the notochord. The anterior notochord, the head process, may represent an intermediate form. The transition from prechordal to chordal mesoderm can be followed by the expression of the two marker homeobox genes goosecoid and Cnot, first in the primitive streak, and then in the head process. We suggest that expression of goosecoid or Cnot is involved in the specification of a prechordal or notochordal identity, respectively. A transition from goosecoid to Cnot expression may proceed, while cells are still in the epiblast, but not after becoming mesodermal. A molecular coding of axial positions in the midline mesoderm may occur by specific homeobox genes, similar to the situation in the neural tube and the somitic mesoderm.
我们分离出了一个鸡的cDNA克隆Cnot，其序列和表达模式与非洲爪蟾的同源框基因Xnot相似。Cnot主要的早期转录结构域包括原结、脊索以及从前脑水平向后的原结前和原结后的神经板。所有这些细胞群体似乎都是原结中表达Cnot的细胞的后代，这表明它们之间存在细胞谱系关系。在体节发生开始后，第二个独立的表达结构域出现在前脑和中脑水平的神经褶中，并且在松果体、腹侧间脑、口前肠和肢芽中也发现了更多的转录本。从延长原条胚胎中移植原结会导致异位脊索的形成，这些异位脊索以典型的、从头部向尾部递减的梯度表达Cnot。之前已经描述过将年轻的原结移植到年轻宿主中会诱导形成次级胚胎。我们观察到，次级鸡胚胎在源自原结的、类似脊索的结构以及前神经板中表达Cnot，这与在初级胚胎中看到的结构域相似。然而，后神经板中没有表达，在诱导实验中，后神经板被排除在原结谱系之外。这一发现证实了我们最初关于由Cnot表达所定义的原结、脊索和神经板之间细胞谱系关系的结论。脊椎动物胚胎的中线中胚层由两种组织组成，即脊索前中胚层和脊索。前脊索，即头部突起，可能代表一种中间形式。从脊索前中胚层到脊索中胚层的转变可以通过两个标记同源框基因goosecoid和Cnot的表达来追踪，首先在原条中表达，然后在头部突起中表达。我们认为，goosecoid或Cnot的表达分别参与了脊索前或脊索身份的特化。在细胞仍处于上胚层时，可能会发生从goosecoid到Cnot表达的转变，但在细胞变成中胚层后则不会。中线中胚层中轴向位置的分子编码可能是由特定的同源框基因完成的，这与神经管和体节中胚层的情况类似。
