Maeda R, Kobayashi A, Sekine R, Lin J J, Kung H, Maéno M
Department of Biology, Faculty of Science, Niigata University, Japan.
Development. 1997 Jul;124(13):2553-60. doi: 10.1242/dev.124.13.2553.
This study analyzes the expression and the function of Xenopus msx-1 (Xmsx-1) in embryos, in relation to the ventralizing activity of bone morphogenetic protein-4 (BMP-4). Expression of Xmsx-1 was increased in UV-treated ventralized embryos and decreased in LiCl-treated dorsalized embryos at the neurula stage (stage 14). Whole-mount in situ hybridization analysis showed that Xmsx-1 is expressed in marginal zone and animal pole areas, laterally and ventrally, but not dorsally, at mid-gastrula (stage 11) and late-gastrula (stage 13) stages. Injection of BMP-4 RNA, but not activin RNA, induced Xmsx-1 expression in the dorsal marginal zone at the early gastrula stage (stage 10+), and introduction of a dominant negative form of BMP-4 receptor RNA suppressed Xmsx-1 expression in animal cap and ventral marginal zone explants at stage 14. Thus, Xmsx-1 is a target gene specifically regulated by BMP-4 signaling. Embryos injected with Xmsx-1 RNA in dorsal blastomeres at the 4-cell stage exhibited a ventralized phenotype, with microcephaly and swollen abdomen. Histological observation and immunostaining revealed that these embryos had a large block of muscle tissue in the dorsal mesodermal area instead of notochord. On the basis of molecular marker analysis, however, the injection of Xmsx-1 RNA did not induce the expression of alpha-globin, nor reduce cardiac alpha-actin in dorsal marginal zone explants. Furthermore, a significant amount of alpha-actin was induced and alpha-globin was turned off in the ventral marginal zone explants injected with Xmsx-1. These results indicated that Xmsx-1 is a target gene of BMP-4 signaling, but possesses a distinct activity on dorsal-ventral patterning of mesodermal tissues.
本研究分析了非洲爪蟾msx - 1（Xmsx - 1）在胚胎中的表达及功能，及其与骨形态发生蛋白4（BMP - 4）腹侧化活性的关系。在神经胚期（第14期），紫外线处理使胚胎腹侧化后Xmsx - 1表达增加，而氯化锂处理使胚胎背侧化后Xmsx - 1表达减少。整体原位杂交分析表明，在原肠胚中期（第11期）和晚期原肠胚（第13期），Xmsx - 1在边缘区和动物极区域表达，位于侧面和腹面，但不在背面。在原肠胚早期（第10 +期），注射BMP - 4 RNA而非激活素RNA可诱导背侧边缘区Xmsx - 1表达，而引入BMP - 4受体RNA的显性负性形式可抑制第14期动物帽和腹侧边缘区外植体中Xmsx - 1的表达。因此，Xmsx - 1是受BMP - 4信号特异性调控的靶基因。在4细胞期将Xmsx - 1 RNA注射到背侧卵裂球中的胚胎表现出腹侧化表型，伴有小头畸形和腹部肿胀。组织学观察和免疫染色显示，这些胚胎在背侧中胚层区域有一大块肌肉组织而非脊索。然而，基于分子标记分析，注射Xmsx - 1 RNA并未诱导α - 珠蛋白表达，也未降低背侧边缘区外植体中的心肌α - 肌动蛋白表达。此外，在注射了Xmsx - 1的腹侧边缘区外植体中诱导了大量α - 肌动蛋白表达且关闭了α - 珠蛋白表达。这些结果表明，Xmsx - 1是BMP - 4信号的靶基因，但在中胚层组织的背腹模式形成中具有独特活性。
