Expression Of The Transcription Factor TBX3 During Development Of Mouse Embryonic Aortic Sac And Arch Arteries

Background:At the 8th embroynic day, with the combine left and right heart tube into one heart tube, the arterial pole of heart tube associated with aortic sac. Aortic sac has sprouted six pairs of arch arteries. Arch arteries are originated from the aortic sac and ended in the dorsal aorta and finally contribute to specific arteries. Six pairs of arch arteries does not occur simultaneously in embryonic mice, the first and second pairs of arch arteries disappear degeneration in early, the fifth pair of arch arteries are hypoplasia and degradation. We mainly observe and study the third, fourth and sixth arch arteries. The aortic arch and major branch arteries are formed from the three pairs of pharyngeal arch arteries during embryonic development. All arch arteries undergo a remodeling process to correctly establish an embryonic and postnatal circulatory system. Asymmetrically programmed regression and persistence of specific arch arteries are involved in the remodeling process. The aortic arch is formed by remodeling of the aortic sac, the left fourth arch artery and left dorsal aorta. The right fourth arch artery contributes to the brachiocephalic artery and proximal part of the right subclavian artery. The left sixth arch artery remodels into the pulmonary trunk and ductus arteriosus, while the right sixth artery regresses and ultimately disappears. The right and left third arch artery reform into the bilateral common carotid arteries. Aortic sac can correctly separated is related to whether can be formed morphologically normal arch arteries, and the arch arteries remodeled and participated in other arterial morphogenesis. T-box containing transcription factors control multiple aspects of embryonic development including morphogenesis and patterning of the heart. Haploinsufficiency or mutation of a number of T-box genes in humans and mice result in congenital heart defects. At least seven family members are expressed in thedeveloping mammalian heart. TBX3 is a T-box transcription factor involved in developmental patterning, regulation of proliferation, senescence, cell cycle exit, and apoptosis. It has been previously reported that TBX3 homozygous mutant embryos are delayed in their overall development compared with littermates. TBX3 deficiency results in variable heart defects including increased cell division in the atrioventricular canal,incomplete ventricular septation, double outlet right ventricle, and delayed aortic arch formation. In the mouse heart, TBX3 expression is first detected in the inflow tract at the onset of heart looping. Its expression delineates the developing cardiac conduction system,endocardial cushions in the atrioventricular canal, and the mesenchyme of the outflow tract.Aortic sac continues with the distal end of outflow tract, the outflow tract of morphogenesis is closely related to the separation of aortic sac.TBX3 is expressed in pharyngeal mesenchyme and cardiac neural crest cells that populate the outflow tract and are involved in its septation. Previous studies on TBX3 more concentrated in the central conduction system in the embryonic heart. TBX3 genetic knockout or mutation in TBX3 in mice leads to working myocardial muscle specific genes in the central sinus node, the atrioventricular node and the atrioventricular bundle of ectopic expression of cardiac conduction system, or formed in atrial or ventricular ectopic rhythm and the role of human ulna and mammary, TBX3 genetic mutations cause ulnar-mammary syndrome in humans.Although reported TBX3 genetic knockout or mutant can cause severe outflow tract abnormalities in mice, including pulmonary trunk and aortic arch anomalies, in previous reported that it was usually appeared as the separation of aortic sac produced by ISL-1positive pharyngeal mesenchyme cells of the second heart field. Although the characteristics of temporal and spatial expression of TBX3 in the second heart field has been described, the reports of separation of aortic sac were lacked. In the development of heart, the transcription factor TBX3 mainly expressed in the cardiac precursor cells of central conduction system. The immunohistochemical method was used in this experiment observe the temporal and spatial expression patterns of antibodies against T-box transcription factor3(TBX3), islet-1(ISL-1) and α-smooth muscle actin(α-SMA) in mouse embryonic hearts from embryonic 9 days to 12 days(E9~E12). The transcriptionfactor TBX3 possible role in the development of aortic sac and arch arteries, which provide morphologic evidence for congenital malformations of aortic arch.Objective:To explore the relationship between transcription factor TBX3(T-box transcription factor) and the development of aortic sac and arch arteries during early development mouse embryo.Methods:Serial paraffin sections of embryonic days 9 ~ 12 mouse hearts(E9 ~ E12) were stained with antibodies against T-box transcription factor3(TBX3), islet-1(ISL-1) andα-smooth muscle actin(α-SMA) by the immunohistochemical method.Results:At E9, TBX3 and ISL-1 positive cells gathered in the pulmonary endoderm. ISL-1positive cells were seen extending to the proximal pole, whereas α-SMA expression is positive in the outflow tract. At E10, with further growth in the outflow tract, α-SMA positive cells extended to invayination of the back wall of pericardial cavity and ISL-1positive cells increased in the pharyngeal endoderm. The proliferative ISL-1 positive cells of branchial arch core mesenchymal add to the communication between aortic sac and third arch arteries. On both sides of pharyngeal mesenchyme TBX3 present strong positive expression. TBX3 and ISL-1 positive cells were observed at the communication between aortic sac and third arch arteries. At E11, α-SMA positive cells were extending from the outflow to the entire aortic sac wall. ISL-1 positive prepharyngeal mesenchyme surrounding the pulmonary endoderm formed a symmetrically distinctive cone-shaped structure,which projected into the aortic sac to form the primary aorta-pulmonary septum primordia. There were TBX3 positive cells in this cone-shaped structure. With the increasing of the second heart field mesenchymal cells number, TBX3 positive cells significantly increased in pharyngeal mesenchyme. The proliferative ISL-1 positive cellsadded to the con-shaped structure. The con-shaped structure elongated longitudinally to the ventral wall of aortic sac which separated aortic sac and form the fourth and sixth arch arteries. Around the fourth and sixth arch arteries where TBX3 positive cells were observed clearly. At E12, outflow tract was shortened. TBX3 and ISL-1 expression was mainly focused on pharyngeal mesenchyme and aortic sac was divided into the ascending aortic artery and pulmonary trunk. Positive expression of α-SMA was observed in the aorta and pulmonary trunk and ends at the root of aortic artery.Conclusions:The cardiac conduction system of positive TBX3 precursor cells and second heart field positive islet factor-1(ISL-1) precursor cells involved in aortic sac morphogenesis. At E10, TBX3 and ISL-1 positive cells participated in the partition of aortic sac and the third arch arteries. At E11, ISL-1 positive cells involved in the formation of aorto-pulmonary septum. TBX3 positive cells were observed around the area of the fourth and sixth arch arteries. At E12, positive expression of α-SMA was observed in wall of the aorta and pulmonary trunk and began to differentiate into smooth muscle.