Early Cardiac Progenitors

点击翻译按钮获取中文摘要

SUMMARY The mammalian heart forms early in embryogenesis, and defects in its formation are at the root of congenital heart defects (CHDs), affecting 1–2% of live births. The gene regulatory networks that are disturbed in CHDs have begun to be elucidated from large-scale human genetic studies. Many of the genes causing CHD are transcriptional regulators, and several of these are also associated with genetics of adult heart disease, such as cardiomyopathy and arrhythmias. A complete understanding of the birth of cardiac progenitors and the first steps that lead to the formation of the embryonic heart has implications for both CHD and adult heart disease. The origins of the heart in embryogenesis have been defined as beginning in mesoderm that arises during gastrulation. We previously defined a specific enhancer of Smarcd3 that labels a very restricted subpopulation of Mesp1 lineage-labeled mesoderm, which contribute almost exclusively to the heart. Embryogenesis is a highly dynamic process, whereby complex coordinated cell movements position organ precursors for precise morphogenesis, and control the response to potent morphogenetic signaling gradients. While aspects of dynamic cardiac morphogenesis have been visualized in the avian embryo, our knowledge of cardiac progenitor emergence and behaviour in the mouse embryo is lacking. We have been able to culture and image live lineage- labeled mouse embryos, and will leverage this exciting approach to investigate mammalian cardiac development. We hypothesize that differentiation, migration, and contribution to early heart formation of early cardiac progenitors are regulated by a specific gene regulatory network composed of temporally-modulated DNA regulatory elements and the coordinated function of a cascade of transcriptional regulators. We will test this hypothesis in two Specific Aims. Specific Aim 1: To define genome-wide the gene regulatory networks that control the emergence of early cardiac progenitors. We will define genome-wide regulatory networks that control the specification, migration, and differentiation of early cardiac precursor using transgenic reporter lines combined with single cell RNA-seq and single cell ATACseq (for chromatin accessibility) in normal and mutant embryonic heart development Specific Aim 2. To visualize the birth and migration of early cardiac progenitors with live embryo imaging. In this aim, we will use live embryo light sheet microscopic imaging of lineage-labeled mouse embryos to visualize in 4D the live dynamic emergence of cardiac progenitors, their migration, and their collective behaviours during early cardiac morphogenesis. We will further image in live embryos in 4D early cardiac progenitors in the context of impaired migration (Mesp1 knockout embryos) and defective differentiation of first or second heart fields (Tbx5 and Mef2c knockout embryos). From transcription factor footprints in the genome, to transcriptomes, to live cells in vivo, our project will elucidate at the single cell level the molecular nature of the earliest cardiac precursors.