Myeloid Zinc Finger 1 (Mzf1) Differentially Modulates Murine Cardiogenesis by Interacting with an <i>Nkx2.5</i> Cardiac Enhancer

<div><p>Vertebrate heart development is strictly regulated by temporal and spatial expression of growth and transcription factors (TFs). We analyzed nine TFs, selected by <i>in silico</i> analysis of an <i>Nkx2.5</i> enhancer, for their ability to transactivate the respective enhancer element that drives, specifically, expression of genes in cardiac progenitor cells (CPCs). <i>Mzf1</i> showed significant activity in reporter assays and bound directly to the <i>Nkx2.5</i> cardiac enhancer (<i>Nkx2.5</i> CE) during murine ES cell differentiation. While Mzf1 is established as a hematopoietic TF, its ability to regulate cardiogenesis is completely unknown. <i>Mzf1</i> expression was significantly enriched in CPCs from <i>in vitro</i> differentiated ES cells and in mouse embryonic hearts. To examine the effect of <i>Mzf1</i> overexpression on CPC formation, we generated a double transgenic, inducible, tetO<i>Mzf1-Nkx2.5</i> CE eGFP ES line. During <i>in vitro</i> differentiation an early and continuous <i>Mzf1</i> overexpression inhibited CPC formation and cardiac gene expression. A late <i>Mzf1</i> overexpression, coincident with a second physiological peak of <i>Mzf1</i> expression, resulted in enhanced cardiogenesis. These findings implicate a novel, temporal-specific role of <i>Mzf1</i> in embryonic heart development. Thereby we add another piece of puzzle in understanding the complex mechanisms of vertebrate cardiac development and progenitor cell differentiation. Consequently, this knowledge will be of critical importance to guide efficient cardiac regenerative strategies and to gain further insights into the molecular basis of congenital heart malformations.</p>