小鼠胚胎心流出道近段心室化形成右心室小梁部

目的探讨小鼠胚胎心流出道快速缩短及右心室形成机制。方法用抗α-横纹肌肌动蛋白(SCA)、抗肌球蛋白重链(MHC)抗体标记心肌,抗GATA-4抗体标记心肌及其前体细胞,抗α-平滑肌肌动蛋白(SMA)抗体标记早期心肌细胞,抗增殖细胞核抗原(PCNA)抗体显示增殖细胞,抗人/鼠活性Caspase-3(CAS-3)抗体检测凋亡早期细胞,对胚龄9d(E9)~E12(不同胚龄胚胎各取3~5只)小鼠胚胎心连续切片行免疫组织化学染色。结果E11时动脉囊及流出道远端心肌界退却至心包腔内,GATA-4、SCA、SMA染色示第二生心区前体细胞不断分化为心肌细胞添加在心动脉端使流出道延长。小鼠胚胎心流出道于E12缩短,缩短前及缩短过程中全长未检测到CAS-3阳性细胞。E10~12时右心室及流出道近段心肌不断增生形成小梁并侵入邻近的流出道嵴内,流出道近端嵴逐渐小梁状心肌化改建为右心室壁;E12时近段间充质性流出道嵴内出现散在的SCA、SMA阳性心肌细胞及与流出道心肌相延续的SCA、SMA弱阳性心肌细胞流,这些结果表明近段流出道心肌小梁化、流出道嵴小梁状肌化形成了右心室小梁部。结论小鼠胚胎流出道近段心室化致右心室小梁部形成及流出道快速缩短,心肌细胞凋亡及转分化对流出道快速缩短的作用甚微。

Ventricularization of the proximal cardiac outflow tract contributes to trabeculated right ventricle in mouse embryo

Objective To explore the mechanism underlying the rapid shortening of outflow tract and the formation of the right ventricle of the embryonic mouse heart. Methods Serial sections of embryonic mouse hearts from embryonic day 9 (E9) to E12（3 to 5 embryos for each stage）were stained with antibodies against α-sarcomeric actin (SCA), α-smooth muscle actin (SMA), GATA-4, myosin heavy chain (MHC), proliferating cell nuclear antigen (PCNA) or active caspase-3 (CAS-3). Results At E11, the aortic sac and the distal border of cardiac outflow tract had regressed towards the ventricle into the pericardial cavity, while GATA-4、SCA and SMA staining showed that precursors from the second heart field were differentiating into cardiomyocytes adding to the arterial pole of the heart to lengthen the outflow tract. The length of outflow tract rapidly shortened at E12. Before and during its shortening, no CAS-3 positive cell was detected in the entire outflow tract. During E10-12, the cardiomyocytes in the right ventricle and proximal outflow tract wall proliferated inward to form trabeculae, with some trabeculae extending into the ridges. Proximal extremities of the outflow tract ridges were gradually myocardialized remodeling into the trabeullar right ventricle wall. At E12, scattered SCA and SMA staining cells and SCA and SMA weak positive mesenchymal cell clusters, which were continuous with the outflow tract myocardium were detected in the mesenchymal proximal outflow tract ridges. These results suggested that the proximal outflow tract was remodeled into the right ventricle by trabecularization, during which mesenchymal ridges were trabecularlly myocardialized. Conclusion Ventricularization of the proximal outflow tract contributes to the trabecular right ventricle and resultes in the
vapid shortening of outflow tract in the mouse embryonic heart. Cardiomyocyte appoptosis and transdifferentiation are found to play a more limited contribution during this process.