ATP-dependent chromatin remodeling complexes are a notable group of epigenetic modifiers that use the energy of ATP hydrolysis to change the structure of chromatin, thereby altering its accessibility to nuclear factors. BAF250a (ARID1a) is a unique and defining subunit of the BAF chromatin remodeling complex with the potential to facilitate chromosome alterations critical during development. Our studies show that ablation of BAF250a in early mouse embryos results in developmental arrest (about embryonic day 6.5) and absence of the mesodermal layer, indicating its critical role in early germ-layer formation. Moreover, BAF250a deficiency compromises ES cell pluripotency, severely inhibits self-renewal, and promotes differentiation into primitive endoderm-like cells under normal feeder-free culture conditions. Interestingly, this phenotype can be partially rescued by the presence of embryonic fibroblast cells. DNA microarray, immunostaining, and RNA analyses revealed that BAF250a-mediated chromatin remodeling contributes to the proper expression of numerous genes involved in ES cell self-renewal, including Sox2, Utf1, and Oct4. Furthermore, the pluripotency defects in BAF250a mutant ES cells appear to be cell lineage-specific. For example, embryoid body-based analyses demonstrated that BAF250a-ablated stem cells are defective in differentiating into fully functional mesoderm-derived cardiomyocytes and adipocytes but are capable of differentiating into ectodermderived neurons. Our results suggest that BAF250a is a key component of the gene regulatory machinery in ES cells controlling self-renewal, differentiation, and cell lineage decisions.BAF250a (ARID1a) ͉ lineage commitment ͉ mesoderm R egulatory factors that control chromatin architecture (directly or indirectly) are potential key proteins for maintaining the pluripotent state or directing differentiation of early embryonic cells into distinct cell types (1). Such factors include ATP-dependent chromatin remodeling complexes that hydrolyze ATP to noncovalently restructure, mobilize, or eject nucleosomes to modulate transcription factor access to chromosomal DNA (2). Among the various members of the ATPdependent chromatin remodeling superfamily is the SWI/SNF subfamily, consisting of two closely related SWI/SNF remodeling complexes BAF and PBAF in mammalian cells (3, 4).BAF250a, a defining subunit of the BAF chromatin remodeling complex (5, 6), is a trithorax group (TrxG) protein (7). TrxG proteins were initially identified by their ability to antagonize the Polycomb group (PcG) proteins to maintain proper expression of many differentiation regulators during development (8). Interestingly, many PcG and TrxG proteins are chromatin modifying factors. Recent studies mapping the targets of PcG action in mouse and human ES cells suggest these proteins also play a role in sustaining a heritable epigenetic state uniquely associated with pluripotency (9, 10).Given the influence of epigenetic factors in determining developmental potential (embryonic development, cellular ...

Dissecting the molecular mechanisms that guide the proper development of epicardial cell lineages is critical for understanding the etiology of both congenital and adult forms of human cardiovascular disease. In this study, we describe the function of BAF180, a polybromo protein in ATP-dependent SWI/SNF chromatin remodeling complexes, in coronary development. Ablation of BAF180 leads to impaired epithelial-to-mesenchymal-transition (EMT) and arrested maturation of epicardium around E11.5. Three-dimensional collagen gel assays revealed that the BAF180 mutant epicardial cells indeed possess significantly compromised migrating and EMT potentials. Consequently, the mutant hearts form abnormal surface nodules and fail to develop the fine and continuous plexus of coronary vessels that cover the entire ventricle around E14. PECAM and *-SMA staining assays indicate that these nodules are defective structures resulting from the failure of endothelial and smooth muscle cells within them to form coronary vessels. PECAM staining also reveal that there are very few coronary vessels inside the myocardium of mutant hearts. Consistent with this, quantitative RT-PCR analysis indicate that the expression of genes involved in FGF, TGF, and VEGF pathways essential for coronary development are down-regulated in mutant hearts. Together, these data reveal for the first time that BAF180 is critical for coronary vessel formation.

Background: Epigenetic mechanisms governing cardiac progenitor cell (CPC) differentiation are not well understood. Results: Chromatin remodeler BAF250a/SWI/SNF regulates CPC differentiation in vivo and in vitro by modeling the chromatin accessibility at a subset of key genes essential for cardiogenesis. Conclusion: BAF250a/SWI/SNF plays a key role in CPC differentiation. Significance: Understanding the SWI/SNF-mediated epigenetic mechanism in CPC differentiation may provide molecular basis for novel heart therapies.