Bachvarova R F, Skromne I, Stern C D
Department of Cell Biology and Anatomy, Cornell University Medical College, New York, NY 10021, USA.
Development. 1998 Sep;125(17):3521-34. doi: 10.1242/dev.125.17.3521.
In the preprimitive streak chick embryo, the search for a region capable of inducing the organizer, equivalent to the Nieuwkoop Center of the amphibian embryo, has focused on Koller's sickle, the hypoblast and the posterior marginal zone. However, no clear evidence for induction of an organizer without contribution from the inducing tissue has been provided for any of these structures. We have used DiI/DiO labeling to establish the fate of midline cells in and around Koller's sickle in the normal embryo. In the epiblast, the boundary between cells that contribute to the streak and those that do not lies at the posterior edge of Koller's sickle, except at stage X when it lies slightly more posteriorly in the epiblast. Hypoblast and endoblast (a second lower layer formed under the streak) have distinct origins in the lower layer, and goosecoid expression distinguishes between them. We then used anterior halves of chick prestreak embryos as recipients for grafts of quail posterior marginal zone; quail cells can be identified subsequently with a quail-specific antibody. Anterior halves alone usually formed a streak, most often from the posterior edge. Quail posterior marginal zones without Koller's sickle were grafted to the anterior side of anterior halves. These grafts were able to increase significantly the frequency of streaks arising from the anterior pole of stage X-XI anterior halves without contributing to the streak or node. Stage XII anterior halves no longer responded. A goosecoid-expressing hypoblast did not form under the induced streak, indicating that it is not required for streak formation. We conclude that the marginal zone posterior to Koller's sickle can induce a streak and node, without contributing cells to the induced streak.
在原条形成前的鸡胚中，寻找能够诱导组织者（相当于两栖类胚胎的Nieuwkoop中心）的区域的研究主要集中在科勒镰刀区、下胚层和后缘区。然而，对于这些结构中的任何一个，都没有提供明确的证据表明在没有诱导组织贡献的情况下能诱导出组织者。我们使用DiI/DiO标记来确定正常胚胎中科勒镰刀区及其周围中线细胞的命运。在胚盘外胚层中，形成原条的细胞和不形成原条的细胞之间的边界位于科勒镰刀区的后缘，但在X期时，该边界在胚盘外胚层中稍靠后。下胚层和内胚层（在原条下方形成的第二层较下层）在下层有不同的起源，并且 goosecoid 表达可区分它们。然后，我们将鸡原条形成前胚胎的前半部分作为鹌鹑后缘区移植的受体；随后可以用鹌鹑特异性抗体识别鹌鹑细胞。单独的前半部分通常会形成原条，最常见的是从后缘开始。将没有科勒镰刀区的鹌鹑后缘区移植到前半部分的前侧。这些移植能够显著增加从X-XI期前半部分的前极产生原条的频率，而不会对原条或节点有贡献。XII期的前半部分不再有反应。在诱导的原条下方没有形成表达goosecoid的下胚层，这表明它不是原条形成所必需的。我们得出结论，科勒镰刀区后方的边缘区可以诱导出原条和节点，而不会向诱导的原条贡献细胞。
