目的 探讨小鼠胚胎心流出道分隔过程中，前肠呼吸内胚层与咽前第二生心区细胞发育的形态学关系及机制。 方法 胚龄9～13d小鼠胚胎标本各6例，连续石蜡切片，用抗转录因子叉头框蛋白A2（Foxa2）、抗胰岛因子1(ISL-1)、抗patched1(Ptc1)、抗patched 2(Ptc2)、抗α-平滑肌肌动蛋白(α-SMA)及抗心肌肌球蛋白重链(MHC)抗体进行免疫组织化学及免疫荧光染色。 结果 胚龄9～9.5d，前肠腹侧壁ISL-1阳性内胚层局部增厚，呼吸内胚层开始发育， ISL-1阳性间充质细胞紧随其后开始出现在呼吸内胚层周围的基质中。胚龄10～11.5d，呼吸内胚层向动脉囊方向生长延伸向喉-气管沟演变，ISL-1阳性咽前间充质细胞围绕呼吸内胚层呈对称的特征性锥体形结构分布，锥体顶端突入动脉囊腔向主-肺动脉隔发育。在喉-气管沟发育过程中，总能观察到1条实心内胚层细胞索位于其腹侧顶端，Ptc1和Ptc2主要局限于发育中的喉-气管沟及实心细胞索表达，喉-气管沟及实心细胞索的内胚层则位于锥体结构的中心。胚龄12～13d，在流出道水平前肠分隔形成气管，内胚层细胞索逐渐消失，气管上皮逐渐失去Ptc1和Ptc2表达，气管腹侧的ISL-1阳性间充质细胞密度明显减低，并逐渐停止向流出道添加，动脉囊分隔完成。 结论 呼吸内胚层的分化发育与咽前ISL-1阳性第二生心区细胞的发育聚集密切耦联。音猬因子（SHH）信号系统在呼吸内胚层发育过程中活跃程度较高，发育中的呼吸内胚层可能作为组织中心，通过SHH信号通路诱导ISL-1阳性细胞的聚集，并通过内胚层生长延伸造成的机械牵拉力驱动ISL-1阳性细胞迁移，参与流出道正常形态发生。

Objective To explore the morphological relationship and mechanism of pulmonary endoderm with the development of the prepharyngeal mesenchyme from second heart field during the outflow tract septation in mouse embryonic heart. Methods Both the immunohistochemical and immunofluorescence staining methods were used to observe forkhead box A2(Foxa2), islet-1(ISL-1), patched-1(Ptc1), patched-2(Ptc2), α-smooth muscle actin(α-SMA）and myosin heavy chain(MHC) distribution in serial sections of six mouse embryos each day from embryonic day(ED) 9 to embryonic day(ED) 13. Results At ED 9-ED 9.5, locally thickened ISL-1 positive endoderm in the ventral foregut wall predicted the initiation of pulmonary endoderm differentiation. As soon as the lanryngo-tracheal groove from pulmonary endoderm was initiated, ISL-1 positive cells began to appear in the matrix surrounding pulmonary endoderm. With the elongation of the lanryngo-tracheal groove in the direction of aortic sac from ED 10 to ED 11.5, ISL-1 positive prepharyngeal cells formed a cone-shaped structure centered by pulmonary endoderm, and its ventral end protruded into the cavity of aortic sac to form aorto-pulmonary septum. During the development of lanryngo-tracheal groove, a solid endoderm cord could always be observed at the ventral end of lanryngo-tracheal groove, and pulmonary endoderm of lanryngo-tracheal groove and its solid cord, to which strong Ptc1 and Ptc2 expression were mainly confined, was located in the center of the ISL-1 cone-shaped structure. From ED 12 to ED 13，separation of foregut at the level of outflow tract led to the formation of trachea, endoderm cord no longer be found and Ptc1 and Ptc2 positive expression disappeared in the tracheal epithelial. The density of the ISL-1 positive mesenchyme cells reduced sharply in the ventral to trachea, which gradually stopped to be added to outflow tract, and aortic sac was separated eventually.  Conclusion The differentiation and development of pulmonary endoderm are closely associated with the ISL-1 positive prepharyngeal mesenchyme of second heart field aggregation. The activity of sonic hedgehog(SHH) signaling system is in a high level during the pulmonary endoderm development, the developing pulmonary endoderm probably acts as an organizing center via SHH pathway to induce aggregation of ISL-1 positive cells, and the mechanical tension produced by endoderm growth is also to drive those ISL-1 positive cells migration for the normal morphogenesis of outflow tract.