Initiation of cardiac differentiation occurs in the absence of anterior endoderm.
Initiation of cardiac differentiation occurs in the absence of anterior endoderm.
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作者：
M. Gannon;D. Bader
已经提出前内胚层是脊椎动物心脏分化的特异性诱导物（综述于Jacobson和Sater，Development 104，341-359，1988）。使用心脏特异性基因表达作为测定来检查心源性中胚层在最小培养系统中分化的能力。前侧板中胚层是从刚在原肠胚形成后的发育阶段（阶段4; Hamburger和汉密尔顿，J. Morph. 88，49-67，1951）到收缩之前（第9阶段）。在检查的所有阶段，心源性中胚层在基本培养基中独立于内胚层的存在两天后表达了心脏特异性mRNA的谱。我们的研究表明，内胚层是产生稳定的肌节蛋白表达，有组织的肌原纤维和跳动的组织从阶段4-6所必需的。在此阶段之后，不再需要与前内胚层的相互作用。检查前内胚层已被单方面删除的心裂胚胎也显示了阶段依赖性的影响内胚层跳动，而心脏基因表达和心脏形态发生不受影响。这些结果表明，前内胚层不诱导或维持心脏基因的表达，也不是终末分化所必需的。在心脏基因表达开始和收缩开始之间的短时间内，内胚层似乎确实是必要的。
Anterior endoderm has been proposed to be a specific inducer of cardiac differentiation in vertebrates (reviewed in Jacobson and Sater, Development 104, 341-359, 1988). The ability of cardiogenic mesoderm to differentiate in a minimal culture system was examined using cardiac-specific gene expression as an assay. Anterior lateral plate mesoderm was explanted from chick embryos with and without associated endoderm at developmental stages from just after gastrulation (stage 4; Hamburger and Hamilton, J. Morph. 88, 49-67, 1951) to just prior to contraction (stage 9). At all stages examined, cardiogenic mesoderm expressed a profile of cardiac-specific mRNAs after two days in minimal medium independent of the presence of endoderm. Our studies indicate that endoderm is necessary for the generation of stable sarcomeric protein expression, organized myofibrils and beating tissue from stage 4-6. Subsequent to this stage, an interaction with anterior endoderm is no longer required. Examination of cardia bifida embryos from which anterior endoderm had been unilaterally removed also showed a stage-dependent effect of endoderm on beating, while cardiac gene expression and heart morphogenesis were unaffected. These results demonstrate that anterior endoderm does not induce or maintain cardiac gene expression, nor is it required for terminal differentiation. Endoderm does appear to be necessary for a short period of time between initiation of cardiac gene expression and the onset of contraction.