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目的探讨小鼠胚胎心脏流出道嵴内α-平滑肌肌动蛋白(α-SMA)阳性细胞的来源及流出道嵴融合时间充质细胞超微结构的变化。方法用抗α-SMA、抗α-横纹肌肌动蛋白(α-SCA)单克隆抗体、PlexinA2探针,对胚龄10～14d小鼠胚胎心脏切片进行免疫组织化学和原位杂交染色;透射电镜观察胚龄12.5d时小鼠心流出道嵴的融合过程。结果胚龄10～11d,小鼠神经管及其周围、动脉囊和弓动脉壁可见PlexinA2阳性细胞,并沿动脉囊壁迁入流出道嵴内,部分细胞同时表达α-SMA。胚龄12d,PlexinA2阳性细胞分布在脊神经节、咽前间充质、主肺动脉隔以及主、肺动脉壁。主肺动脉隔显α-SMA强阳性,但动脉壁仅见少量α-SMA阳性细胞。胚龄12.5d,流出道嵴内致密间充质细胞团形成并开始融合,PlexinA2表达较弱,α-SMA表达呈强阳性。在流出道嵴融合开始后,嵴表面的内皮细胞带形成继而断裂消失,由含微丝少、排列稀疏的间充质细胞取代。两侧致密细胞团逐渐靠拢、融合。有的间充质细胞内含较多线粒体和微丝,细胞之间形成细胞连接点;有的间充质细胞含微丝少,细胞膜间断融合。结论流出道心内膜垫内α-SMA阳性间充质细胞来自神经嵴;内皮细胞-间充质细胞转化可能参与了流出道嵴融合;致密细胞团内间充质细胞富含微丝束和细胞连接点或发生细胞膜融合有助于流出道嵴的融合。
Objective To investigate the origin of α-smooth muscle actin (α-SMA) positive cells and the changes of the ultrastructure of mesenchymal cells in the outflow crest in mouse embryonic cardiac outflow tract. Methods Immunohistochemistry and in situ hybridization staining of mouse embryonic heart sections from 10 to 14 days old with anti-α-SMA, anti-α-striated actin (α-SCA) monoclonal antibody and PlexinA2 probe were performed. Transmission electron microscopy The fusion process of cardiac outflow cristae was observed at embryonic day 12.5d. Results PlexinA2 positive cells were observed in the neural tube and its surrounding, arterial sac and the artery wall of the mouse at embryonic day 10 to 11, and migrated into the crest of the outflow tract along the arterial wall. Some of the cells also expressed α-SMA. The embryo age 12d, PlexinA2 positive cells were distributed in the spinal ganglia, pharyngeal anterior mesenchyme, the main pulmonary artery septum and the main, pulmonary artery wall. The main pulmonary artery was significantly positive for α-SMA, but only a small amount of α-SMA positive cells in the arterial wall. At embryonic age 12.5d, the dense mesenchymal cell mass in the outflow ridges formed and started to fuse. The expression of PlexinA2 was weak and the expression of α-SMA was strongly positive. After outflow ridge merging began, the endothelial cell bands on the ridge surface formed and then disappeared, replaced by sparse mesenchymal cells with fewer filaments. Compact cell clusters on both sides gradually move closer, fusion. Some mesenchymal cells contain more mitochondria and microfilaments, cells forming cell junctions; some mesenchymal cells with less microfilaments, intermittent fusion of the cell membrane. Conclusions The α-SMA positive mesenchymal cells in the outflow tract endocardial cushion originate from the neural crest. The endothelial cell mesenchymal transition may be involved in the outflow ridge fusion. The dense mesenchyme in the dense cell mass is rich in microfilament bundles and Cell junctions or cell membrane fusion contribute to the fusion of outflow crest.