Abstract 16207: RNA Polymerase II-associated Factor 1 Complex Drives Cardiac Progenitor Formation and Differentiation

Cardiac differentiation from pluripotent progenitor cells requires well-orchestrated transcriptional and epigenetic regulations. The evolutionarily conserved RNA polymerase II-associated factor 1 complex (PAF1C) functions as a transcription platform required for a wide range of cell signaling processes. From zebrafish genetic screens, we identify critical roles for PAF1C in the formation and differentiation of cardiac progenitor cells. Overexpression of Rtf1, a PAF1C component, activates cardiac transcription program and promotes the formation of cardiac progenitor cells in zebrafish. Conversely, knockdown of Rtf1 prevents cardiac differentiation in mouse embryonic stem cells and Rtf1 ablation in zebrafish and mice eliminates the entire cardiac progenitor population resulting in a heartless embryo. Molecular dissection identifies the histone modification and DNA binding domains of Rtf1. Structure-function analysis in zebrafish reveals distinct requirements for these domains in heart development; the DNA binding domain of Rtf1 is essential for the specification of the cardiac fate whereas the histone modification domain is dispensable for the formation of cardiac progenitor cells, but is required for the maturation of cardiomyocytes. Chromatin immunoprecipitation and luciferase reporter assays show that Rtf1 regulates the expression of cardiac transcription factors such as Nkx2.5 and Tbx20 by direct interaction with these promoters via the DNA binding domain. In addition, mutations in the histone modification domain reduce the abundance of epigenetic marks associated with actively transcribed genes and compromise the maturation of cardiomyocytes. Together these findings demonstrate that Rtf1 regulates cardiac differentiation by controlling transcription and epigenetic modification.