Development of the Secondary Heart Field

描述（由申请人提供）：先天性心脏病是所有出生缺陷中最常见的，由“心脏或胸内大血管的总体结构异常”引起。要了解先天性心脏病的病因，了解正常心脏发育是至关重要的。我们最近通过研究lim同源结构域转录因子islet1 （isl1）发现了心脏发育的新范式。isl1纯合子缺失的小鼠胚胎期死亡，心脏明显异常。详细的组织学和标记分析表明，isl突变心脏缺乏流出道、右心室和相对较少的心房组织，isl不在原代心脏新月中表达，而是在邻近的中胚层细胞群中表达。令人惊讶的是，对isl表达细胞的谱系分析表明，isl的后代在胚胎心脏中产生流出道、右心室和大多数心房细胞。总之，我们的结果需要重新定义继发心田，因为它比以前怀疑的要广泛得多，胰岛的表达既标志着重新定义的继发心田，也是继发心田产生胚胎心脏主要部分所必需的。在isl突变体中，似乎有更少的胰岛表达细胞，许多成纤维细胞和骨形态发生蛋白生长因子的表达在继发性心脏区下调。这些观察结果表明，胰岛通过调节FGF和BMP生长因子途径，决定了心脏祖细胞在继发性心脏领域的生长、存活、迁移和特异性。该研究将通过进一步研究isl突变表型，以及在继发性心脏场中选择性消融FGF和BMP受体来验证这一假设。我们的实验将对维持心源性干细胞状态所需的途径，以及二级心脏场产生的心脏内不同谱系的规范所需的途径产生新的见解。

DESCRIPTION (provided by applicant): Congenital heart disease is the most common of all birth defects, and results from a "gross structural abnormality of the heart or intrathoracic great vessels". To understand the etiology of congenital heart disease, it is of utmost importance to understand normal heart development. We have recently discovered a new paradigm for heart development, through studies of a LIM-homeodomain transcription factor, islet1 (isl1). Mice homozygous null for isl1 die embryonically, with strikingly abnormal hearts. Detailed histological and marker analysis has demonstrated that isl mutant hearts are lacking an outflow tract, right ventricle, and have relatively little atrial tissue, isl is not expressed in the primary cardiac crescent but rather is expressed in a population of adjacent mesendodermal cells. Surprisingly, lineage analysis of isl expressing cells has demonstrated that descendents of isl give rise to the outflow tract, right ventricle, and a majority of atrial cells in the embryonic heart. Together, our results necessitate a redefinition of the secondary heart field, as being far more extensive than previously suspected, islet expression both marks this redefined secondary heart field, and is required for the secondary heart field to give rise to major segments of the embryonic heart. In isl mutants, there appear to be fewer islet expressing cells, and expression of a number of fibroblast and bone morphogenetic protein growth factors is downregulated in the secondary heart field. These observations suggest the hypothesis that islet dictates growth, survival, migration, and specification of cardiac progenitors in the secondary heart field by its regulation of FGF and BMP growth factor pathways. The proposed studies will investigate this hypothesis by further studies of the isl mutant phenotype, and selective ablation of FGF and BMP receptors within the secondary heart field. Our experiments will yield novel insight into pathways required for maintenance of the cardiogenic stem cell state, and pathways required for specification of distinct lineages within the heart which arise from secondary heart field.