Green J B, Smith J C, Gerhart J C
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Development. 1994 Aug;120(8):2271-8. doi: 10.1242/dev.120.8.2271.
The growth factor activin elicits mesodermal fates when applied to prospective ectodermal cells of the Xenopus blastula stage embryo. Previous experiments with dissociated cells showed that there are at least five different responses separated by closely spaced, sharp dose thresholds. Here we investigate this multithreshold activin response further using probes for genes expressed at early gastrula stages, namely Xbra, goosecoid, noggin, Xwnt-8 and Mix.1. We show that initial dose-response profiles are broad and smooth in contrast to the later threshold-bound patterns. For Xbra, goosecoid and noggin, the later expression ranges are subsets of earlier ones. Unexpectedly, Xwnt-8 is initially induced at high doses only, but later appears only in cells that have received a low dose of activin. Keeping the cells dissociated after activin treatment, rather than allowing them to reaggregate, prevents sustained expression of Xbra and Xwnt-8 but allows that of goosecoid and noggin. However, cell contact is required for sharpening the dose-response threshold of goosecoid. Finally, we show that a previously reported dorsoventral prepattern in the animal cap is also cell-contact dependent and it is not required for the multi-threshold response to activin.
当将生长因子激活素应用于非洲爪蟾囊胚期胚胎的预期外胚层细胞时，它会引发中胚层命运。先前对解离细胞进行的实验表明，至少存在五种不同的反应，这些反应由间隔紧密、尖锐的剂量阈值分隔开。在这里，我们使用原肠胚早期表达的基因探针，即Xbra、鹅膏蕈氨酸、头蛋白、Xwnt - 8和Mix.1，进一步研究这种多阈值激活素反应。我们发现，与后期的阈值界限模式相比，初始剂量 - 反应曲线是宽泛且平滑的。对于Xbra、鹅膏蕈氨酸和头蛋白，后期的表达范围是早期表达范围的子集。出乎意料的是，Xwnt - 8最初仅在高剂量时被诱导，但后期仅出现在接受低剂量激活素的细胞中。激活素处理后保持细胞解离，而不是让它们重新聚集，会阻止Xbra和Xwnt - 8的持续表达，但允许鹅膏蕈氨酸和头蛋白的持续表达。然而，细胞接触是锐化鹅膏蕈氨酸剂量 - 反应阈值所必需的。最后，我们表明，先前报道的动物帽中的背腹预模式也是细胞接触依赖性的，并且它对于激活素的多阈值反应不是必需的。
