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胰岛（Isl1）在心脏祖细胞发育过程中起着关键作用，也在啮齿动物和人类心脏的出生后心脏祖细胞中表达。在心脏发生过程中，Isl1是第二心野祖细胞增殖、存活和迁移所必需的，在心源性中胚层和咽内胚层中均有表达。目前尚不清楚早期心脏发育是否需要中胚层或内胚层中的Isl1。尽管isl1在进入心脏的绝大多数祖细胞中下调，但最近的研究表明，isl1在心脏的不同亚域中持续表达，包括流出道和窦房结的心肌谱系。Isl1在选定的分化心肌谱系中的持续存在表明对Isl1的后期需求尚未探索。本提案中有待验证的假设是，在心脏发育和功能的特定方面，内胚层、心源性中胚层和分化心肌细胞的亚结构域需要Isl1，并且确定Isl1的直接或间接靶点将为心脏发生过程中Isl1的作用提供机制见解。本研究的具体目的是：(1)利用Mesp1-cre或Foxa2诱导的cre，以及Isl1的一个固定等位基因，确定Isl1在中胚层祖细胞或咽内胚层中的组织特异性需求；(2)利用前心田特异性cre （MEF2c-cre）或传导系统特异性诱导cre （HCN4-CreERT2）和一个锁定的Isl1等位基因消融分化心肌谱系中的Isl1，研究Isl1在分化心肌谱系中的潜在作用；(3)通过识别早期心脏发生过程中Isl1的直接和间接下游靶点，深入了解Isl1控制细胞行为的机制。这些研究结果将为心脏发育过程中Isl1控制细胞行为和形态发生的途径提供机制见解。

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.