Role of TBX20 in endocardial cushion formation during chick heart development

T-box基因家族包含一个约200个氨基酸的DNA结合区(T-box)，是转录因子的新成员。T-box基因被认为与许多发育过程有关。我们从鸡胚胎中分离到一个Tbx20基因，并发现它在胚胎心脏中有很强的表达。原位杂交结果显示，Tbx20基因在心脏前中胚层表达，之后在心脏环状结构中，其转录产物定位于流出道(OT)、心球、房室管和心房。此外，Tbx20基因在OT区和房室区心内膜垫组织中有较强的表达。提示Tbx20基因可能在心脏发生中起重要作用。Tbx2、-5和-20在心房发育过程中均有表达。发育解剖学表明，右、左心房由静脉窦、原始心房和心脏背侧系膜发育而来，经历了静脉窦与心房并入、房间隔发育和肺静脉发育等一系列胚胎过程。然而，调控这些过程的机制仍不清楚。我们用原位杂交的方法检测了Tbx2、-5、-20在14-27期发育中的心房中的表达模式。结果提示，Tbx2、-5、-20的差异表达可能在房间隔、肺静脉发育等心房发育中起重要作用。然后，为了确定Tbx20是否对缓冲组织的形成是必需的，我们构建了Tbx20-Engrailed2(Tbx20的显性阴性形式)，并在胶原凝胶晶格上将Tbx20导入第13期心脏的房室外植体。结果表明，Tbx20修饰的Tbx2在体外可抑制内皮细胞向间充质细胞的转化。这些结果表明，Tbx20在雏鸡心脏发育过程中可能在缓冲组织的形成中起重要作用。

The T-box gene family, which contains a DNA-binding domain of about 200 amino acids (T-box), is a new member of transcription factors. T-box genes thought to be concerned with many developmental processes. We have isolated a Tbx20 gene from chick embryo and found its strong expression in the embryonic heart. In situ hybridization showed that Tbx20 gene expressed in the precardiac mesoderm, and thereafter, in the looped heart, its transcripts were localized in the outflow tract (OT), bulbus cordis, atrioventricular (AV) canal and atrium. Moreover Tbx20 gene expressed strongly in the endocardial cushion tissue of OT and AV regions. Results suggest that Tbx20 gene may play an imporatant role in the cardiogenesis. And Tbx2,-5 and -20 were expressed during atrium development. Developmental anatomy shows that right and left atrium are developed from the sinus venosus, primitive atrium and dorsal mesocardium via the sequential embryonic processes such as, incorporation of the sinus venosus to the atrium, atrial septation and pulmonary venous development. However, mechanisms regulating these processes remain unknown. We examined expression patterns of Tbx2,-5,-20 in the developing atrium from stage 14 to 27 by in situ hybridization. Results suggest that differentially expressed Tbx2,-5,-20 may play an important role in the atrial development, such as septation and pulmonary venous development. Then, to determine whether Tbx20 is necessary for cushion tissue formation, we constructed Tbx20-engrailed2 (dominant negative form to Tbx20) and transfected into AV explants of stage 13 hearts on collagen gel lattice. Results indicated that Tbx20-engrailed2 inhibited endothelial to mesencymal transformation in vitro. These results suggested that Tbx20 may play a important role in cushion tissue formation during chick heart development.