Transcription factor EBF1 non-cell autonomously regulates cardiac growth and differentiation
Reciprocal interactions between non-myocytes and cardiomyocytes are implicated in the control of cardiac growth and differentiation.  Here, we report the identification of early B-cell factor 1 (Ebf1) as a transcription factor highly enriched in non-myocytes that potently regulates heart development.  Postnatal Ebf1 deficient hearts are characterized by marked myocardial hypercellularity and reduced cardiomyocyte size, as well as ventricular conduction system hypoplasia and conduction system disease.  Growth abnormalities in Ebf1 knockout hearts are observed as early as embryonic day 13.5, with dysregulated cell cycling, myocardial hyperplasia, and immature trabecular morphology.  Transcriptional profiling of Ebf1-deficient non-myocytes isolated from embryonic hearts demonstrates dysregulation of Polycomb repressive complex 2 (PRC2) targets, while ATAC-Seq reveals differences in chromatin accessibility near many of these same genes. Gene set enrichment analysis of differentially expressed genes in cardiomyocytes isolated from E13.5 hearts of wildtype and Ebf1 deficientmice reveals significant enrichment of MYC targets, and consistent with this finding, we observe increased abundance of MYC in mutant hearts.  Mechanistically, we show that EBF1-deficient non-myocytes, but not wildtype non-myocytes, are sufficient to induce excessive accumulation of nuclear-localized MYC protein in co-cultured wildtype cardiomyocytes. Finally, we demonstrate that BMP signaling induces Ebf1 expression in embryonic heart cultures and controls a gene program enriched in EBF1 targets.  Taken together, these results reveal a novel non-cell autonomous pathway controlling cardiac growth and development. Overall design: Gene transcirptional profiling was performed on embryonic day 13.5 mouse heart cells after dissociation and FACS sorting using PECAM1 antibody and TMRM dye to identify endocardial cells and cardiomyocytes respectively. ATAC-Seq was performed on non-myocyte cells from E13.5 mouse hearts isolated by preplating.