Reduced dosage of β-catenin genetically rescues intracardiac anomalies in a Tbx1 conditional null mouse model of 22q11.2 deletion syndrome. Mus musculus

Approximately 60-70% of patients with 22q11.2 deletion syndrome (22q11.2DS; velo-cardio-facial syndrome/DiGeorge syndrome) have cardiac outflow tract anomalies including persistent truncus arteriosus (PTA) as the most severe defect. Among the genes in the 22q11.2 region, TBX1, encoding a T-box transcription factor is a major candidate for cardiovascular malformations and its inactivation in mice results in a PTA. To identify novel signaling mechanisms that function downstream, we found that Tbx1 restricts canonical Wnt signaling in the pharyngeal apparatus. To test for tissue specificity within the pharyngeal apparatus, we inactivated Tbx1 in the anterior portion of the secondary heart field (AHF) mesoderm using the Mef2c-AHF-Cre allele and observed a full penetrant PTA (n = 30). Tbx1 promotes progenitor cells but restricts differentiation whereas Wnt signaling, in the AHF, promotes cardiomyocyte differentiation. To determine whether Tbx1 and canonical Wnt signaling act in opposing pathways, both alleles of Tbx1 and one β-catenin allele were inactivated in the AHF and 85% of them (n = 35) showed partial or complete rescue. The antagonistic function of the two pathways was further confirmed by gene expression profiling, indicating that these two pathways provide a key balance in the AHF to prevent premature differentiation of progenitor cells prior to reaching the cardiac outflow tract. Overall design: We inactivatedTbx1 and beta-catenin allele to identify function of Tbx1 and beta-catenin in the anterior portion of the secondary heart field (AHF) mesoderm. We also inactivated both alleles of Tbx1 and one β-catenin alleles (rescue design) to determine whether Tbx1 and canonical Wnt signaling act in opposing pathways

约60%-70%的22q11.2缺失综合征（22q11.2 deletion syndrome, 22q11.2DS；又称腭心面综合征/迪乔治综合征）患者存在心脏流出道畸形，其中以永存动脉干（persistent truncus arteriosus, PTA）为最严重的表型缺陷。在22q11.2区域的基因中，编码T-box转录因子的TBX1是心血管畸形的主要候选致病基因，且该基因在小鼠体内失活可诱导出永存动脉干表型。为鉴定其下游调控的新型信号通路机制，本研究发现Tbx1可在咽区结构（pharyngeal apparatus）中抑制经典Wnt信号通路。为验证该调控作用在咽区结构内的组织特异性，本研究借助Mef2c-AHF-Cre等位基因，在次级心区前部（anterior portion of the secondary heart field, AHF）中胚层特异性敲除Tbx1，结果显示所有受试小鼠（n=30）均出现完全外显的永存动脉干表型。Tbx1可促进祖细胞增殖却抑制其分化，而次级心区中的Wnt信号通路则可促进心肌细胞分化。为验证Tbx1与经典Wnt信号通路是否呈拮抗调控关系，本研究在次级心区中同时敲除Tbx1的两个等位基因与一个β-连环蛋白（β-catenin）等位基因，结果显示85%的受试小鼠（n=35）的表型得到部分或完全挽救。基因表达谱分析进一步验证了两条通路的拮抗作用，提示这两条通路在次级心区中形成关键的平衡机制，以阻止祖细胞在抵达心脏流出道前提前分化。研究设计：本研究通过敲除次级心区前部中胚层的Tbx1与β-连环蛋白等位基因，以明确二者在该区域的功能；同时通过同时敲除Tbx1双等位基因与单个β-连环蛋白等位基因（挽救实验设计），验证Tbx1与经典Wnt信号通路是否存在拮抗调控关系