GSE172511
hapln1 defines an epicardial cell subpopulation that establishes cardiogenic hotspots during heart morphogenesis and regeneration
The epicardium, a thin mesothelial tissue layer that encompasses the heart, is a dynamic structure that is essential for cardiac regeneration in species with elevated regenerative capacity like zebrafish. To dissect epicardial cell states and associated pro-regenerative functions, we performed single-cell RNA-sequencing and identified 7 epicardial cell clusters in adult zebrafish, with 3 of these clusters enhanced during regeneration. ECM components encoded by hapln1 paralogs label an enriched epicardial cell type that accumulates and encloses dedifferentiated and proliferating cardiomyocytes during regeneration. Genetic inactivation of hapln1b, or induced genetic depletion of hapln1a-expressing cells, disrupted cardiomyocyte proliferation and heart regeneration.  hapln1a+ cells first emerge at the juvenile stage, when they associate with and are required for cardiogenic foci that direct growth of the juvenile heart. Our findings identify a subset of epicardial cells that emerges in post-embryonic animals and sponsors regions of active cardiomyogenesis during heart growth and regeneration Overall design: Single cell RNA sequencing of FACS isolated eppicaridal cells  (tcf21:nucEGFP) from uninjured and regenerating hearts