Role of TBX20 in endocardial cushion formation during chick heart development

T-box基因家族是转录因子家族中的一个新成员，含有一个约200个氨基酸的DNA结合域（T-box）。T盒基因被认为与许多发育过程有关。我们从鸡胚中分离到一个Tbx 20基因，发现它在鸡胚心脏中有强表达。原位杂交结果显示，Tbx 20基因表达于心前区中胚层，在环状心脏中，其转录产物定位于流出道、心球、房室管和心房。Tbx 20基因在OT区和AV区的内膜垫组织中表达较强。结果提示Tbx 20基因可能在心肌发生中起重要作用。Tbx 2、-5和-20在心房发育过程中均有表达。发育解剖学研究表明，右心房和左心房是由静脉窦、原始心房和背侧系膜经过静脉窦并入心房、心房分隔和肺静脉发育等顺序的胚胎过程发育而来的。然而，调节这些过程的机制仍然未知。我们通过原位杂交检测了Tbx 2，-5，-20在发育14 - 27期心房中的表达模式。结果提示，Tbx 2、-5、-20在心房发育过程中可能起重要作用，如心房分隔和肺静脉的发育。然后，为了确定Tbx 20是否是垫组织形成所必需的，我们构建了Tbx 20-锚定2（Tbx 20的显性阴性形式）并转染到胶原凝胶网格上的13期心脏的AV外植体中。结果表明，Tbx 20-enrailed 2抑制内皮细胞到间质细胞的转化在体外。这些结果表明，Tbx 20可能在鸡心脏发育过程中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.