小鼠胚胎心脏房室管心内膜垫发育的形态学特征

Morphological characteristics of atrioventricular endocardial cushion development of the mouse embryonic heart

目的探讨小鼠胚胎心脏房室管心内膜垫的形成与融合过程中的形态学特征。方法选用抗α-平滑肌肌动蛋白（α-SMA）、抗心肌肌球蛋白重链（MHC）、抗磷酸化组蛋白H3（PHH3）抗体,对30只胚龄9~13d小鼠胚胎连续切片进行HE和免疫组织化学染色。另选15只胚龄12d、12.5d、13d小鼠胚胎心脏制作半薄切片和超薄切片进行观察。结果胚龄9d,心房与心室之间可见缩窄的房室管,房室管的心胶质较厚,但未见间充质细胞出现。胚龄10d,房室管心内膜垫开始形成,但连续切片观察显示背侧心内膜垫体积大于腹侧心内膜垫,且背侧心内膜垫对应的α-SMA、MHC阳性房室管心肌向心内膜垫内有明显延伸。心内膜垫内间充质细胞不表达α-SMA或PHH3。胚龄11~12d,背、腹侧心内膜垫变得对称,垫内间充质细胞增多,偶见α-SMA或PHH3阳性细胞。胚龄12~13d,两侧房室管心内膜垫彼此接近开始融合。透射电子显微镜下观察仅部分间充质细胞相邻细胞膜彼此相贴,局部形成细胞连接。胞质内可见粗面内质网、线粒体等细胞器,微丝较少。结论小鼠胚胎心脏房室管心内膜垫形成时首先表现为内皮细胞由扁平变为立方形;两侧房室管心内膜垫形成不同步;房室管心内膜垫融合时间充质细胞局部形成细胞连接,胞质内微丝少,与流出道嵴融合时的超微结构特点不同。

Objective To investigate the morphological characteristics of the formation and the fusion pattern of atrioventricular endocardial cushion of mouse embryonic heart. Methods Serial sections of thirty mouse embryos during embryonic day（ ED） 9 to ED13 were stained immunohistochemically with antibodies against α-smooth muscle actin（ α-SMA）,myosin heavy chain（ MHC） and phosphorylated histone H3（ PHH3）. Semithin sections and ultrathin sections of fifteen mouse embryonic hearts from ED12 to ED13 were observed by light microscope and transmission electron microscopy. Results At ED9,the atrioventricular canal was observed between the atrium and the ventricle. The cardiac jelly layer was thickened and contained a few mesenchymal cells. At ED10,the atrioventricular endocardial cushion began to form. The inferior endocardial cushion was thicker than the superior cushion. The α-SMA and MHC positive myocardial cells neighboring with the inferior cushions extended towards the cushion. The mesenchymal cells in the cushions showed α-SMA or PHH3 negative. During ED11 to ED12,the inferior and superior cushions became symmetric and the mesenchymal cells increased obviously. Only a few of mesenchymal cells expressed α-SMA or PHH3. At ED12 and ED13,the bilateral cushions closed to each other and began to fuse. The cellular membrane touched each other and formed intercellular junctions between some mesenchymal cells. The mesenchymal cells contained rough endoplasmic reticulum and mitochondria,and few of microfilament were observed in the cells. Conclusion The first change of atrioventricular endocardial cushion formation of mouse embryonic heart is the morphologic change of the endothelial cell from squamous to cuboidal. The formation of the two endocardial cushions is not simultaneous. During the cushion fusion,cellular junction is formed locally between mesenchymal cells which contain few of microfilament. Thus ultrastructure characteristics of thefusion of the atrioventricular endocardial cushion is different with the outflow tract ridge.