Bhushan A, Chen Y, Vale W
Clayton Foundation Laboratories for Peptide Biology, Salk Institute, 10010 North Torrey Pines Road, La Jolla, California, 92037, USA.
Dev Biol. 1998 Aug 15;200(2):260-8. doi: 10.1006/dbio.1998.8965.
We report the isolation and characterization of a new inhibitory Smad in Xenopus, which we have designated as Xenopus Smad7. Smad7 is present at fairly constant levels throughout early development and at blastula stages enriched in the ventral side of the animal hemisphere. The induction of mesoderm by TGF-beta-like signals is mediated by receptor ALK-4 and we show that Smad7 blocks signaling of ALK-4 in a graded fashion: lower levels of Smad7 block activation of dorsal mesoderm genes and higher levels block all mesoderm genes expression. Smad7 is able to directly activate neural markers in explants in the absence of mesoderm or endoderm. This neural-inducing activity of Smad7 may be due to inhibition of BMP-4 signaling because Smad7 can also block BMP-4-mediated mesoderm induction. Thus, Smad7 acts as a potent inhibitor of mesoderm formation and also activates the default neural induction pathway.
我们报告了非洲爪蟾中一种新的抑制性Smad的分离与特性鉴定，我们将其命名为非洲爪蟾Smad7。在整个早期发育过程中，Smad7的水平相当恒定，在囊胚期，它在动物半球的腹侧富集。TGF-β样信号诱导中胚层是由受体ALK-4介导的，我们发现Smad7以分级方式阻断ALK-4的信号传导：较低水平的Smad7阻断背侧中胚层基因的激活，较高水平的Smad7阻断所有中胚层基因的表达。在没有中胚层或内胚层的情况下，Smad7能够直接激活外植体中的神经标记物。Smad7的这种神经诱导活性可能是由于抑制了BMP-4信号传导，因为Smad7也能阻断BMP-4介导的中胚层诱导。因此，Smad7作为中胚层形成的有效抑制剂，还激活了默认的神经诱导途径。
