The Development Of The Atrioventricular Canal And The Expression Pattern Of Lef1 In Mouse Embryonic Heart

ChapterⅠ The development of the atrioventricular canal and the expression pattern of Lef1 in mouse embryonic heartObjective:To investigate the septation and remodeling of the atrioventricula r canal and the expression pattern of Lef1 in mouse embryonic heart.Methods:Serial sections of twenty-five mouse embryos during embryonic day(ED)10 to ED15 were stained immunohistochemistry and immunofluorescence with antibodies against myosin light chain 2a(MLC2a),myosin regulatory light chain 2(MLC-2),T-box transcription factor 3(Tbx3)and lymphoid enhancer-binding factor 1(Lef1).Results:Immunohistochemistry and immunofluorescence staining for MLC2 a,Tbx3 and Lef1 showed that atrioventricular canal myocardium of mouse embryonic day 10 to day 15 were positive results,but for MLC2 was negative result.At ED10,the atrioventricular endocardial cushion was formed.During ED11 to ED12,Lef1 was highly expressed in the mesenchymal cells of the atrioventricular cushion.The epicardium began to be observed.At ED12 and ED13 of mouse,the bilateral atrioventricular canal cushions began to fuse each other and formed the atrioventricular valve.In the epicardium the mesenchymal cells derived from between the atrioventricular myocardium and epicardium were increased,a part of which showed the Lef1 immunohistochemistry positive staining.From ED 13 of mouse embryo,a part cells of epicardium derived from mesenchymal cells traversed through the myocardium to parietal atrioventricular valve.At ED15,the base of the atrioventricular valve was directly connected with the MLC2 a positive atrioventricular myocardium.Conclusion:The atrioventricular myocardium develops into the myocardium to support the base of the valves of the adult atrioventricular ring.Lef1 is expressed in the myocardium and epicardium derived mesenchymal cells during the process of the endocardial cushion fusion and the atrioventricular valve formation.ChapterⅡ Tbx3 and the development of the second heart field in mouse embryoObjective:To investigate the expression pattern and significance of Tbx3 in the SHF of mouse embryo.Methods:Serial sections of thirty mouse embryos during ED9 to ED15 were stained immunohistochemistry and immunofluorescence with antibodies against islet-1(isl1),myosin heavy chain(MHC),myosin light chain 2a(MLC2a),T-box transcription factor 3(Tbx3).Results:During ED10 to ED12,isl1 positive mesenchymal cells in pharynx ventral mesenchyme were increased gradually.At the stages,the expression of Tbx3 in endoderm of ventral pharynx was down-regulated,whereas the expression began to be seen in the mesenchyme cells adjacent to the ventral endoderm.During ED9 to ED11,isl1 positive cells in pharynx ventral mesenchyme were continuous with those in the aortic sac wall,pericardial dorsal wall and the distal outflow tract wall,where Tbx3 was negative.And MHC was weakly positive in the distal pole of the outflow tract wall.In the venous pole of the embryonic heart,isl1 positive cells of pharynx ventral mesenchyme extended to DMP through the dorsal mesocardium and Tbx3 positive cells was shown in DMP.During ED12 to ED13,in the arterial pole,isl1 positive cells of SHF extended to the septated arterial walls,and the latter was lack of Tbx3 expression.In the venous pole,DMP gradually began to be myocardialized,where Tbx3 positive cells were observed.At ED15,myocardialization of DMP was completed.Tbx3 positive cells in DMP were continuous with those of the atrioventricular bundle at the top of the interventricular septum.Conclusion:Tbx3 did not directly regulate the migration and differentiation of SHF precursor cells,but it may regulate the existence and proliferation of these cells.The regulation in p SHF may be different with that in the anterior SHF.