中文摘要：

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，流出道嵴内致密问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。

英文摘要：

Objective To investigate the origin of α-SMA positive cells in the outflow tract ridge of the embyonic mouse heart and to explore the ultrastructure change of the mesenchymal cells during the ridges fusion. Methods Sections of embryonic day 10（E10d） to E14d mouse embryonic hearts were stained by immunohistochemistry assay with monoclonal antibodies against α-smooth muscle aetin （α-SMA） , α-sarcomeric aetin （α-SCA） and in situ hybridization method with PlexinA2 probe. The outflow tract ridges fusion was observed by transmission electron microscopy at E12.5d. Results From E10d to Elld, PlexinA2 positive cells were seen in the neural tube with mesenchymes around it, the aortic sac and aortic arch. These cells also migrated into the outflow tract ridge along the aortic sac wall and part of them expressed α- SMA. At E12d, PlexinA2 was expressed in the spinal ganglia, the pharyngeal mesenchyme, the aorto-pulmonary septum and the ascending aorta and pulmonary trunk. The septum showed α-SMA strongly positive. But only a few of α-SMA positive cells were observed in the ascending aorta and pulmonary trunk. At E12.5d, two clusters of condensed mesenchymal cells in the outflow tract ridges formed and began to express PlexinA2 weakly and α-SMA strongly. When the ridges began to fuse, the endothelial cells formed a cellular seam, which rapidly broke into pieces and disappeared and were replaced by the sparsed mesenchymal cells containing a few of microfilaments. Two clusters of condensed mesenchymal cells gradully moved to merge. It was noted that some mesenchymal cells contained plenty of microfilament bundles, mitochondria and focal contacts between them. Some mesenchymal cells only had a few of microfilaments and plasma membrane fusion was seen between them. Conclusion α-SMA positive cells in the outflow tract cushion may be derived from cardiac neural crest. The endothelial cells might participate in the fusion of the outflow tract ridges by endothelialmesenchymal transformation. Mesenchymal cells of