Essential and unexpected role of YY1 to promote mesodermal cardiac differentiation. Mus musculus

Rationale: Cardiogenesis is regulated by a complex interplay between transcription factors and chromatin-modifying enzymes. However, little is known about how these interactions regulate the transition from mesodermal precursors to cardiac progenitor cells (CPCs). Objective: To identify novel regulators of mesodermal cardiac lineage commitment. Methods and Results: We performed a bioinformatic-based transcription factor-binding site analysis on upstream promoter regions of genes that are enriched in ES cell-derived CPCs. From 32 candidate transcription factors screened, we found that YY1, a repressor of sarcomeric gene expression, is present in CPCs in vivo. Interestingly, we uncovered the ability of YY1 to transcriptionally activate Nkx2.5, a key marker of early cardiogenic commitment. YY1 regulates Nkx2.5 expression via a 2.1 kb cardiac-specific enhancer as demonstrated by in vitro luciferase-based assays and in vivo chromatin immunoprecipitation (ChIP) and genome-wide sequencing analysis. Furthermore, the ability of YY1 to activate Nkx2.5 expression depends on its cooperative interaction with GATA4 at a nearby chromatin. Cardiac mesoderm-specific loss-of-function of YY1 resulted in early embryonic lethality. This was corroborated in vitro by ES cell-based assays where we show that the over-expression of YY1 enhanced the cardiogenic differentiation ES cells into CPCs in a cell autonomous manner. Conclusion: These results demonstrate an essential and unexpected role for YY1 to promote cardiogenesis as a transcriptional activator of Nkx2.5 and other CPC-enriched genes. Overall design: We report the identification of putative YY1 target genes in cardiac progenitor cells (CPCs). Two samples of independently FACS-purified eGFP+ CPCs were examined against the input.