what is the role of MEF-2 in cardiomyocyte differentiation?
The myocyte enhancer factor-2 (MEF2) proteins are MADS-box transcription factors that are essential for differentiation of all muscle lineages but their mechanisms of action remain largely undefined. MEF2C expression initiates cardiomyogenesis, resulting in the up-regulation of Brachyury T, bone morphogenetic protein-4, Nkx2-5, GATA-4, cardiac alpha-actin, and myosin heavy chain expression. Inactivation of the MEF2C gene causes cardiac developmental arrest and severe downregulation of a number of cardiac markers including atrial natriuretic factor (ANF). BMP-2, a regulator of cardiac development during embryogenesis, was shown to increase PI 3-kinase activity in cardiac precursor cells, resulting in increased expression of sarcomeric myosin heavy chain (MHC) and MEF-2A. Furthermore, expression of MEF-2A increased MHC expression in a PI 3-kinase-dependent manner. Other studies showed that Gli2 and MEF2C proteins form a complex, capable of synergizing on cardiomyogenesis-related promoters. Dominant interference of calcineurin/mAKAP binding blunts the increase in MEF2 transcriptional activity seen during myoblast differentiation, as well as the expression of endogenous MEF2-target genes. These findings show that MEF-2 can direct early stages of cell differentiation into a cardiomyogenic pathway.