Suzuki H R, Solursh M, Baldwin H S
Department of Biological Sciences, University of Iowa, Iowa City 52242, USA.
Dev Dyn. 1995 Nov;204(3):259-77. doi: 10.1002/aja.1002040305.
By utilizing myosin immunostaining, we were able to identify early rat myocardium as a thin epithelial sheet and realized that its cohesive movement toward the midline leads to the straight heart tube formation. Localization study of fibronectin mRNA and protein was, therefore, carried out to investigate its tissue origin and possible roles in facilitating mesoderm migration and heart formation. Fibronectin mRNAs were first detected throughout the mesoderm during the early primitive streak stage, suggesting that the mesoderm is the source of fibronectin. By pre-head fold (pre-somite) and head fold (early somite) stages, the mesoderm became largely down-regulated for fibronectin mRNAs, while it was also at these stages when myosin-positive myocardium formed itself into the epithelium and was subsequently folding toward the midline. Thus, there appears to be little fibronectin synthesis during and directly relevant to early heart tube formation. Later, during the early straight heart tube stage (5 somite and older), endocardium became highly positive for fibronectin mRNAs, suggesting that the endocardium is the major source of fibronectin for the cardiac jelly. Based on the results, we present a map for the early mammalian heart in which the heart is a single crescentic band lying in front of the prechordal plate. We also suggest a process for heart tube formation based on the cohesive movement of the myocardial epithelium. During heart tube formation, fibronectin protein had been deposited previously by the mesoderm and was found uniformly in the ECM and not newly produced by any adjacent tissue. The data contradict the endodermal guidance of heart migration by fibronectin gradient and suggest, instead, a permissive role for the fibronectin substrate.
通过利用肌球蛋白免疫染色，我们能够将早期大鼠心肌识别为一层薄的上皮片，并认识到其向中线的凝聚运动导致了直心管的形成。因此，进行了纤连蛋白mRNA和蛋白质的定位研究，以探讨其组织来源以及在促进中胚层迁移和心脏形成中的可能作用。在原始条纹早期，纤连蛋白mRNA首先在整个中胚层中被检测到，这表明中胚层是纤连蛋白的来源。在前头褶（前体节）和头褶（早期体节）阶段，中胚层中纤连蛋白mRNA的表达大幅下调，而也正是在这些阶段，肌球蛋白阳性的心肌形成上皮并随后向中线折叠。因此，在早期心管形成期间及与之直接相关的过程中，似乎很少有纤连蛋白的合成。后来，在早期直心管阶段（5体节及更晚），心内膜中纤连蛋白mRNA呈高度阳性，这表明心内膜是心脏胶冻中纤连蛋白的主要来源。基于这些结果，我们展示了早期哺乳动物心脏的图谱，其中心脏是位于脊索板前方的单一新月形带。我们还基于心肌上皮的凝聚运动提出了心管形成的过程。在心管形成过程中，纤连蛋白蛋白先前已由中胚层沉积，并且在细胞外基质中均匀分布，并非由任何相邻组织新产生。这些数据与纤连蛋白梯度对心脏迁移的内胚层引导相矛盾，相反，表明纤连蛋白底物起许可作用。
