Mechanisms of Islet1 Action in Heart Development

描述（由申请人提供）：了解心脏祖细胞通路与先天性和成人心脏病相关。LIM同源结构域转录因子Islet（Isl 1）在发育过程中的心脏祖细胞中起关键作用，并且还在啮齿动物和人类心脏中发现的出生后心脏祖细胞中表达。在心脏发生过程中，Isl 1是第二心脏领域祖细胞增殖、存活和迁移所必需的，并且在心源性中胚层和咽内胚层中表达。目前尚不清楚Isl 1是否需要在中胚层或内胚层的早期心脏发育。虽然Isl 1在绝大多数祖细胞进入心脏时下调，但最近的研究表明Isl 1在心脏内不同的亚区域中持续表达，包括流出道和窦房结的心肌谱系。在选定的分化心肌谱系中Isl 1的持续性表明，Isl 1尚未被探索的后期需求。在这个提议中要测试的假设是，Isl 1是需要在内胚层，心源性中胚层，并在分化的心肌细胞的亚域的心脏发育和功能的特定方面，并定义直接或间接的目标Isl 1将给予机械的洞察Isl 1的行动在心脏发生。（1）利用Mesp 1-cre或Foxa 2诱导的cre和isl 1的floxed等位基因，确定Isl 1在中胚层祖细胞或咽内胚层中的组织特异性需求;（2）通过利用前心野特异性CRE消融分化心肌谱系中的Isl 1，研究Isl 1在分化心肌谱系中的潜在作用。（MEF 2c-cre）或传导系统特异性诱导的cre（HCN 4-CreERT 2），以及Isl 1的floxed等位基因;和（3）通过鉴定早期心脏发生期间Isl 1的直接和间接下游靶标，深入了解Isl 1控制细胞行为的机制。这些研究的结果将提供机制洞察Isl 1控制细胞行为和心脏发育过程中的形态发生的途径。 公共卫生相关性Isl 1是一种标记未分化心脏祖细胞的转录因子，是其增殖、分化和迁移所必需的。Isl 1也在咽内胚层中表达，其与心源性中胚层相邻并作为诱导物。拟议的研究将提供关于在心脏发生过程中Isl 1在何处、何时以及如何影响细胞行为的机制见解。

DESCRIPTION (provided by applicant): Understanding cardiac progenitor pathways is relevant for both congenital and adult heart disease. The LIM homeodomain transcription factor Islet (Isl1) plays a pivotal role in cardiac progenitors during development, and is also expressed in postnatal cardiac progenitors found in rodent and human heart. During cardiogenesis, Isl1 is required for proliferation, survival, and migration of second heart field progenitors, and is expressed both within cardiogenic mesoderm and pharyngeal endoderm. It is not known whether Isl1 is required within mesoderm or endoderm for early heart development. Although isl1 is downregulated in the great majority of progenitors as they enter the heart, recent studies have demonstrated persistent Isl1 expression in distinct subdomains within the heart, including myocardial lineages of the outflow tract and sinoatrial node. Persistence of Isl1 in selected differentiated myocardial lineages suggests later requirements for Isl1 which have not been explored. The hypothesis to be tested in this proposal is that Isl1 is required in endoderm, cardiogenic mesoderm, and in subdomains of differentiated cardiomyocytes for specific aspects of heart development and function, and that defining direct or indirect targets of Isl1 will give mechanistic insights into Isl1 action during cardiogenesis. The Specific Aims of this proposal are: (1) To determine tissue specific requirements for Isl1 in mesodermal progenitors or pharyngeal endoderm, utilizing Mesp1-cre or Foxa2- inducible cre, and a floxed allele of isl1; (2) To investigate a potential role for Isl1 in differentiated myocardial lineages by ablation of isl1 in differentiated myocardial lineages utilizing an anterior heart field specific-cre (MEF2c-cre) or a conduction system specific-inducible cre (HCN4-CreERT2), and a floxed allele of isl1; and (3) To gain insight into mechanisms by which Isl1 controls cell behaviors, by identifying direct and indirect downstream targets of Isl1 during early cardiogenesis. Results of these studies will give mechanistic insight into pathways by which Isl1 controls cell behaviors and morphogenesis during heart development. PUBLIC HEALTH RELEVANCE Isl1 is a transcription factor which marks undifferentiated cardiac progenitors and is required for their proliferation, differentiation and migration. Isl1 is also expressed in pharyngeal endoderm, which is adjacent to cardiogenic mesoderm and acts as an inducer. The proposed studies will provide mechanistic insight as to where, when, and how Isl1 is required to effect cell behaviors during cardiogenesis.