Smith J C, Slack J M
J Embryol Exp Morphol. 1983 Dec;78:299-317.
We have studied the action of the organizer in Xenopus laevis using grafts labelled with horseradish peroxidase (HRP). Orthotropic grafts of the dorsal marginal zone (the organizer) from an HRP-labelled embryo into an unlabelled host showed that this region contributes to the anterior archenteron wall, to the entire craniocaudal extent of the notochord and to a few cells in the somites. Little or no contribution was made to the neural tube. Orthotopic grafts of the ventral marginal zone (the tissue that responds to a grafted organizer) indicated that it only contributes to the posterior half of the embryo. Within this region it spreads around the entire ventrolateral mesoderm, occasionally contributing a few cells to the somites. The posterior endoderm was also heavily labelled. When the dorsal marginal zone from an HRP-labelled embryo was inserted into a slit cut in the ventral marginal zone of an unlabelled host a mirror-symmetrical double-dorsal duplicated embryo resulted, in which only the notochord and a few cells in the somites of the secondary embryo were derived from the graft. The bulk of the secondary somites was, therefore, derived from host ventral marginal zone tissue which normally makes very little contribution to the somites. This indicates that host ventral marginal zone becomes dorsalized by the graft. The neural tube of the secondary embryo was also unlabelled, showing that it was induced by the influence of the graft on the overlying ectoderm, which normally forms ventral epidermis. We have also grafted ventral marginal zone tissue into a slit cut into the dorsal marginal zone of a host embryo. HRP-labelled tissue was grafted into an unlabelled embryo and vice versa. This graft did not produce a double ventral embryo and this reinforces the traditional view that the dorsal marginal zone is a special signalling region. Instead, the resulting embryos usually had a twinned notochord with the graft tissue in between, differentiated as somite. This confirms that juxtaposing ventral and dorsal marginal zone 'dorsalizes' the ventral tissue but does not affect the dorsal tissue which differentiates, as usual, as notochord. Thus, our results allow us to conclude that the organizer mediates two distinct interactions in bringing about the formation of duplicated embryos. The first is dorsalization of adjacent ventral mesoderm and the second is the induction of neuroepithelium from ectoderm overlying the new archenteron roof.
我们利用辣根过氧化物酶（HRP）标记的移植片，研究了非洲爪蟾中组织者的作用。将来自HRP标记胚胎的背侧边缘区（组织者）进行同位移植到未标记的宿主中，结果表明该区域对原肠前壁、脊索的整个头尾范围以及体节中的少数细胞有贡献。对神经管的贡献很小或没有贡献。腹侧边缘区（对移植的组织者作出反应的组织）的同位移植表明，它仅对胚胎的后半部分有贡献。在该区域内，它围绕整个腹外侧中胚层扩散，偶尔对体节贡献少数细胞。后端内胚层也被大量标记。当将来自HRP标记胚胎的背侧边缘区插入未标记宿主腹侧边缘区切开的缝隙中时，会产生一个镜像对称的双背侧重复胚胎，其中只有次生胚胎的脊索和体节中的少数细胞来自移植片。因此，次生体节的大部分来自宿主腹侧边缘区组织，而该组织通常对体节的贡献很小。这表明宿主腹侧边缘区被移植片背化。次生胚胎的神经管也未被标记，这表明它是由移植片对上方外胚层的影响诱导形成的，而该外胚层通常形成腹侧表皮。我们还将腹侧边缘区组织移植到宿主胚胎背侧边缘区切开的缝隙中。将HRP标记的组织移植到未标记的胚胎中，反之亦然。这种移植没有产生双腹侧胚胎，这强化了传统观点，即背侧边缘区是一个特殊的信号区域。相反，产生的胚胎通常有一个双脊索，移植组织位于两者之间，并分化为体节。这证实了将腹侧和背侧边缘区并列会使腹侧组织“背化”，但不会影响通常分化为脊索的背侧组织。因此，我们的结果使我们能够得出结论，组织者在导致重复胚胎形成过程中介导了两种不同的相互作用。第一种是相邻腹侧中胚层的背化，第二种是从新原肠顶上方的外胚层诱导神经上皮的形成。
