Waldrip W R, Bikoff E K, Hoodless P A, Wrana J L, Robertson E J
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Cell. 1998 Mar 20;92(6):797-808. doi: 10.1016/s0092-8674(00)81407-5.
Smad proteins transmit TGFbeta signals from the cell surface to the nucleus. Here we analyze Smad2 mutant embryos created using ES cell technology. Smad2 function is not required for mesoderm production per se, but, rather unexpectedly, in the absence of Smad2 the entire epiblast adopts a mesodermal fate giving rise to a normal yolk sac and fetal blood cells. In contrast, Smad2 mutants entirely lack tissues of the embryonic germ layers. Smad2 signals serve to restrict the site of primitive streak formation and establish anterior-posterior identity within the epiblast. Chimera experiments demonstrate these essential activities are contributed by the extraembryonic tissues. Thus, the extraembryonic tissues play critical roles in establishing the body plan during early mouse development.
Smad蛋白将转化生长因子β（TGFβ）信号从细胞表面传递至细胞核。在此，我们分析了利用胚胎干细胞（ES细胞）技术构建的Smad2突变胚胎。中胚层的产生本身并不需要Smad2发挥功能，但出乎意料的是，在缺乏Smad2的情况下，整个上胚层都呈现中胚层命运，进而形成正常的卵黄囊和胎儿血细胞。相比之下，Smad2突变体完全缺乏胚胎胚层组织。Smad2信号有助于限制原条形成的位置，并在上胚层内建立前后轴身份。嵌合体实验表明，这些重要活动是由胚外组织发挥作用的。因此，在小鼠早期发育过程中，胚外组织在建立身体蓝图方面发挥着关键作用。
