ES cell pluripotency and germ-layer formation require the SWI/SNF chromatin remodeling component BAF250a

Abstract

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 ...

Loss of ARID1A expression and its relationship with PI3K-Akt pathway alterations, TP53 and microsatellite instability in endometrial cancer

“…This finding corresponds to a study that showed altered levels of SWI/SNF subunit expression in mouse ES cells with knockout of one or both alleles of ARID1A. 34 Taken together, these data suggest that SMARCB1 and SMARCD3 expression are not independently affected in endometrial cancer, but the expression level may be reduced when the stability of the SWI/ SNF complex is disturbed because of ARID1A loss.…”

NuRD Blocks Reprogramming of Mouse Somatic Cells into Pluripotent Stem Cells

“…For example, the SWI/SNF remodeling complex BAF (BRG1-associated factor) promotes iPSC generation by increasing binding of reprogramming factors to the promoters of pluripotent genes [11]. Homozygous knockout or knockdown of any of several BAF subunits results in defects in ESC self-renewal and differentiation, highlighting their critical roles in maintaining the ESC gene expression pattern [10]. Here, we show that NuRD, a well-characterized corepressor complex that represses transcription in a variety of developmental contexts, blocks epigenetic resetting during the transition of somatic cells into iPSCs by silencing some pluripotency-associated genes.…”

“…Consistent with epigenetic reprogramming playing a key role in cell-fate conversion, small molecules that target chromatin-modifying enzymes greatly enhance reprogramming efficiency, yielding iPSCs that are similar to ESCs [7][8][9]. An ESC-specific chromatin remodeling complex, esBAF (embryonic stem cell specific Brg/Brahmaassociated factor), has been shown to be important for the maintenance of pluripotency and the differentiation capacity of ESCs [10,11]. However, the epigenetic pathways that orchestrate chromatin remodeling of specific target genes remain largely unknown.…”

The SWI/SNF complex and cancer

“…A dominant-negative BRG1 allele blocks myeloid differentiation of 32Dcl3 cells (Vradii et al, 2006), whereas loss of BRG1 in keratinocytes results in defects in limb patterning (Indra et al, 2005). Studies in embryonic stem cells have revealed that lack of BAF250 can compromise cell pluripotency and severely inhibit self-renewal, whereas functional BAF250 contributes to the proper expression of numerous genes involved in embryonic stem cell self-renewal, including Sox2, Utf1 and Oct4 (Yan et al, 2008) (Gao et al, 2008). Furthermore, pluripotency defects in BAF250a mutant embryonic stem cells appear to be cell lineage specific (Gao et al, 2008;Yan et al, 2008).…”

“…Studies in embryonic stem cells have revealed that lack of BAF250 can compromise cell pluripotency and severely inhibit self-renewal, whereas functional BAF250 contributes to the proper expression of numerous genes involved in embryonic stem cell self-renewal, including Sox2, Utf1 and Oct4 (Yan et al, 2008) (Gao et al, 2008). Furthermore, pluripotency defects in BAF250a mutant embryonic stem cells appear to be cell lineage specific (Gao et al, 2008;Yan et al, 2008). Thus, SWI/ SNF activity appears to be essential for differentiation in yeasts, flies and mammals.…”