Lawrence P A, Bodmer R, Vincent J P
Medical Research Council, Laboratory of Molecular Biology, Cambridge, UK.
Development. 1995 Dec;121(12):4303-8. doi: 10.1242/dev.121.12.4303.
The mesoderm of Drosophila embryos is segmented; for instance there are segmentally arranged clusters of cells (some of which are heart precursors) that express even-skipped. Expression of even-skipped depends on Wingless, a secreted molecule. In principle, Wingless could act directly in the mesoderm or it could induce the pattern after crossing from ectoderm to mesoderm. Using mosaic embryos, we show that Wingless produced in the mesoderm is sufficient for even-skipped expression. This proves that induction is not essential. However, induction can occur: when patches of wingless mutant mesoderm are overlaid by wild-type ectoderm, they do express even-skipped. We therefore believe that Wingless from both the ectoderm and mesoderm may contribute to patterning the mesoderm. Using the UAS/Gal4 system, we made embryos in which the Wingless protein is uniformly expressed. This is sufficient to rescue the repeated clusters of even-skipped expressing cells, although they are enlarged. We conclude that the mesoderm is segmented in some way not dependent on the distribution of Wingless, suggesting a more permissive and less instructive role for the protein in this instance.
果蝇胚胎的中胚层是分段的；例如，存在呈分段排列的细胞簇（其中一些是心脏前体），这些细胞簇表达偶数跳基因（even-skipped）。偶数跳基因的表达依赖于无翅基因（Wingless），一种分泌分子。原则上，无翅基因可以直接作用于中胚层，或者它可以在从外胚层进入中胚层后诱导这种模式。利用镶嵌胚胎，我们发现中胚层产生的无翅基因足以实现偶数跳基因的表达。这证明诱导并非必不可少。然而，诱导是可以发生的：当无翅基因突变的中胚层区域被野生型外胚层覆盖时，它们确实会表达偶数跳基因。因此，我们认为来自外胚层和中胚层的无翅基因可能都有助于中胚层的模式形成。利用UAS/Gal4系统，我们构建了无翅蛋白均匀表达的胚胎。这足以挽救表达偶数跳基因的细胞的重复簇，尽管它们变大了。我们得出结论，中胚层以某种不依赖于无翅基因分布的方式进行分段，这表明在这种情况下该蛋白的作用更具许可性且指导性较弱。
