Domingo C, Keller R
Department of Biology, San Francisco State University, San Francisco, California, 94132, USA.
Dev Biol. 2000 Sep 1;225(1):226-40. doi: 10.1006/dbio.2000.9769.
During gastrulation, the vertebrate embryo is patterned and shaped by complex signaling pathways and morphogenetic movements. One of the first regions defined during gastrulation is the prospective notochord, which exhibits specific cell behaviors that drive the extension of the embryonic axis. To examine the signals involved in notochord formation in Xenopus laevis and the competence of cells to respond to these signals, we performed cell transplantation experiments during gastrulation. Labeled cells from the prospective notochord, somitic mesoderm, ventrolateral mesoderm, neural ectoderm, and epidermis, between stages 9 (pregastrulation) and 12 (late gastrulation), were grafted into the prospective notochord region of the early gastrula. We show that cells from each region are competent to respond to notochord-inducing signals and differentiate into notochordal tissue. Cells from the prospective neural ectoderm are the most responsive to notochord-inducing signals, whereas cells from the ventrolateral and epidermal regions are the least responsive. We show that at the end of gastrulation, while transplanted cells lose their competence to form notochord, they remain competent to form somites. These results demonstrate that at the end of gastrulation cell fates are not restricted within germ layers. To determine whether notochord-inducing signals are present throughout gastrulation, grafts were made into progressively older host embryos. We found that regardless of the age of the host, grafted cells from each region give rise to notochordal tissue. This indicates that notochord-inducing signals are present throughout gastrulation and that these signals overlap with somite-inducing signals at the end of gastrulation. We conclude that it is the change of competence that restricts cells to specific tissues rather than the regulation of the inducing signals.
在原肠胚形成过程中，脊椎动物胚胎通过复杂的信号通路和形态发生运动来形成模式并塑造形态。原肠胚形成过程中最早确定的区域之一是预期的脊索，它表现出特定的细胞行为，驱动胚胎轴的延伸。为了研究非洲爪蟾中参与脊索形成的信号以及细胞对这些信号的反应能力，我们在原肠胚形成期间进行了细胞移植实验。在第9期（原肠胚形成前期）和第12期（原肠胚形成后期）之间，将来自预期脊索、体节中胚层、腹外侧中胚层、神经外胚层和表皮的标记细胞移植到早期原肠胚的预期脊索区域。我们发现，每个区域的细胞都有能力对诱导脊索形成的信号作出反应并分化为脊索组织。来自预期神经外胚层的细胞对诱导脊索形成的信号反应最为敏感，而来自腹外侧和表皮区域的细胞反应最不敏感。我们发现，在原肠胚形成结束时，虽然移植细胞失去了形成脊索的能力，但它们仍然有能力形成体节。这些结果表明，在原肠胚形成结束时，细胞命运并不局限于胚层内。为了确定在整个原肠胚形成过程中是否都存在诱导脊索形成的信号，我们将细胞移植到逐渐发育成熟的宿主胚胎中。我们发现，无论宿主的年龄如何，来自每个区域的移植细胞都能形成脊索组织。这表明在整个原肠胚形成过程中都存在诱导脊索形成的信号，并且这些信号在原肠胚形成结束时与诱导体节形成的信号重叠。我们得出结论，是反应能力的变化将细胞限制在特定组织中，而不是诱导信号的调控。
