The Development Of Atrium And Posterior Second Heart Field In Mouse Embryo

Objective:To investigate the distribution pattern of ISL-1 positive posterior second heart field(p SHF), the formation of dorsal mesenchymal protrusion(DMP) and its contribution to atrium septation in mouse embryonic heart.Methods:Serial sections of mouse embryos during embryonic day(ED) 9 to ED15 were stained immunohistochemically with antibodies against α-smooth muscle actin(α-SMA), myosin heavy chain(MHC), Islet1(ISL-1) and Nkx2.5.Results:From ED9 to ED12, the ISL-1 positive cells located in the pharyngeal mesenchyme, splanchnic mesoderm of the pericardial cavity dorsal wall, dorsal mesocardium, sinuatrial node and valve of the caval vein. At ED13, ISL-1 positive cells only distributed in the wall of the intrapericardial right caval vein and sinuatrial node. After ED14, the ISL-1 positive cells were not detectable in the atrium and the caval vein wall. During ED10 and ED11, dorsal mesenchymal protrusion(DMP) was formed. The sporadic ISL-1 positive cells were located at dorsal mesocardium and extended into the DMP. At ED12, DMP fused with atrio-ventricular cushion and septum primum. From ED9 to ED10, the left and right common cardinal vein connected symmetrically with venous sinus horn. During ED13 to ED15, the myocardialization was observed in DMP, the wall of intrapericardial caval vein and coronary sinus.Conclusion:ISL-1 positive precursor cells of posterior Second Heart Field shows different distribution pattern during the different development period, and participate in the development of atrial, sinuatrial node and wall of the caval vein. DMP is derived from the posterior Second Heart Field. When the atrio-ventricular cushions became close to each other and fused to septate the atrio-ventricular canal, DMP fused with the septum primum and the atrio-ventricular cushion to take part in the closing of foramen primum. Myocardialization of DMP is completed by myocardial cell migration of the septum primum. Different gene expression pattern was shown between the coronary sinus and the right caval vein. The myocardiolization mechanism was also different between them.