转录因子Nkx2.5、ISL-1表达与小鼠胚胎心的早期发育

Expression patterns of Nkx2.5 and ISL-1 during early development of mouse embryonic heart

目的：探讨转录因子Nkx2.5和ISL-1的表达与小鼠胚胎早期心发育的关系.方法：胚龄7.5～13d小鼠胚胎连续石蜡切片,用抗α-平滑肌肌动蛋白（α-SMA）、抗心肌肌球蛋白重链（MHC）、抗转录因子ISL-1、抗Nkx2.5抗体,进行免疫组织化学显色.结果：转录因子Nkx2.5在胚龄7.5d生心板表达早于心肌特异性蛋白MHC及SMA.随心外形建立,Nkx2.5在心各部表达逐渐增强.胚龄9d, Nkx2.5阳性表达从原始心管动脉端延伸至心包腔背侧脏壁中胚层及咽周围轴旁中胚层.Isl-1开始表达于胚龄8d原始心管心背系膜及前肠腹侧脏壁中胚层间充质,阳性细胞数量在11～12d达顶峰,形成前肠腹侧连接流出道远端和心房背侧壁的ISL-1阳性细胞带.11～12d,流出道远端出现Nkx2.5和MHC阴性,ISL-1、SMA阳性表达区.胚龄13d后,Nkx2.5和ISL-1在心和前肠腹侧间充质的表达强度下降.结论：Nkx2.5是原始生心区心肌前体细胞早期分化的标记蛋白,在第2生心区表达限于胚龄9d、咽周脏壁和轴旁中胚层心肌前体细胞亚群.第2生心区标记蛋白ISL-1主要表达在胚龄8～12d前肠腹侧脏壁中胚层心肌前体细胞,并向心管添加心肌细胞,参与流出道发育及心管成襻.11d后,第2生心区间充质细胞开始分化为升主动脉和肺动脉干平滑肌.

Objective： To investigate the relationship of Nkx2.5 and ISL-1 expression with early development of the mouse embryonic heart. Methods： Serial sections of mouse embryos from embryonic day （ED） 7.5 to ED 13 were stained with antibodies against ccSMA, MHC, Nkx2.5 and ISL-1. Results： At ED 7.5, the expression of Nkx2.5 was found in the cardiogenie plate, earlier than that of heart specific proteins, MHC and SMA. Following morphological establishment of heart, the expression of Nkx2.5 in the heart became stronger. Moreover, at ED 9, the Nkx2.5 expression could be seen extending from the arterial pole of the primary heart tube to the splanchnic mesoderm dorsal to the pericardial cavity and paraxial mesoderm around the primary pharynx. The initial expression of ISL-1 was detected in the dorsal mesocardium and the splanchnic mesoderm of the dorsal pericardial cavity wall ventral to the foregut at ED 8. The number of ISL-1 positive cells reached highest level at ED 11-12, forming a continuous band ventral to the foregut that connected the distal pole of the outflow tract with the dorsal wall of the atrium. At ED 11-12, the cells in the distal pole of the outflow tract gradually shed Nkx2.5 and MHC expression with increasing SMA and ISL-1 expression. After ED 13, the expression of Nkx2.5 in the heart and ISL- 1 in mesenchymal cells ventral to the foregut gradually decreased. Conclusion： Nkx2. 5 is an early marker of the cardiac precursor cells in the primary heart field, its expression in the second heart field subset is confined to the splanchnic mesoderm and paraxial mesoderm surrounding the pharynx at ED 9. Confinement of the expression of the second heart field marker ISL-1 to the splanchnic mesoderm ventral to the foregut during the period of ED 8 to ED 12 and addition myocardial cells to the developing heart from the second heart field during this period suggest that the second heart field subset is involved in the development of the outflow tract myocardium and heart looping. After ED 11, the mesenchymal cells derived from the second heart field begin differentiating into smooth muscle in the walls of the aorta and pulmonary trunk.