Furue Miho, Myoishi Yasufumi, Fukui Yasuto, Ariizumi Takashi, Okamoto Tetsuji, Asashima Makoto
Department of Biochemistry and Molecular Biology, Kanagawa Dental College, Yokosuka 238-8580, Japan.
Proc Natl Acad Sci U S A. 2002 Nov 26;99(24):15474-9. doi: 10.1073/pnas.242597399. Epub 2002 Nov 7.
Activin A has potent mesoderm-inducing activity in amphibian embryos and induces various mesodermal tissues in vitro from the isolated presumptive ectoderm. By using a sandwich culture method established to examine activin A activity, we previously demonstrated that activin-treated ectoderm can function as both a head and trunk-tail organizer, depending on the concentration of activin A. By using activin A and undifferentiated presumptive ectoderm, it is theoretically possible to reproduce embryonic induction. Here, we test this hypothesis by studying the induction of cartilage tissue by using the sandwich-culture method. In the sandwiched explants, the mesenchymal cell condensation expressed type II collagen and cartilage homeoprotein-1 mRNA, and subsequently, cartilage were induced as they are in vivo. goosecoid (gsc) mRNA was prominently expressed in the cartilage in the explants. Xenopus distal-less 4 (X-dll4) mRNA was expressed throughout the explants. In Xenopus embryos, gsc expression is restricted to the cartilage of the lower jaw, and X-dll4 is widely expressed in the ventral head region, including craniofacial cartilage. These finding suggest that the craniofacial cartilage, especially lower jaw cartilage, was induced in the activin-treated sandwiched explants. In addition, a normal developmental pattern was recapitulated at the histological and genetic level. This work also suggests that the craniofacial cartilage-induction pathway is downstream of activin A. This study presents a model system suitable for the in vitro analysis of craniofacial cartilage induction in vertebrates.
激活素A在两栖类胚胎中具有强大的中胚层诱导活性，并能在体外从分离的预定外胚层诱导出各种中胚层组织。通过使用为检测激活素A活性而建立的夹心培养方法，我们之前证明，根据激活素A的浓度，经激活素处理的外胚层可同时发挥头部和躯干-尾部组织者的功能。从理论上讲，利用激活素A和未分化的预定外胚层有可能重现胚胎诱导过程。在此，我们通过使用夹心培养方法研究软骨组织的诱导来验证这一假设。在夹心外植体中，间充质细胞凝聚表达II型胶原蛋白和软骨同源蛋白-1 mRNA，随后，如在体内一样诱导出软骨。鹅膏蕈氨酸（gsc）mRNA在外植体的软骨中显著表达。非洲爪蟾远端缺失4（X-dll4）mRNA在整个外植体中表达。在非洲爪蟾胚胎中，gsc表达局限于下颌软骨，而X-dll4在包括颅面软骨在内的腹侧头部区域广泛表达。这些发现表明，在经激活素处理的夹心外植体中诱导出了颅面软骨，尤其是下颌软骨。此外，在组织学和基因水平上重现了正常的发育模式。这项工作还表明，颅面软骨诱导途径位于激活素A的下游。本研究提出了一个适用于体外分析脊椎动物颅面软骨诱导的模型系统。
