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Chromatin remodeler Brahma safeguards labile canalization of cardiac mesoderm differentiation

ABSTRACT: Differentiation proceeds along a continuum of increasingly fate-restricted intermediates, referred to as canalization. Canalization is essential for stabilizing cell fate, but mechanisms underlying robust canalization are unclear. Here we show that the BRG1/BRM-associated factor (BAF) chromatin remodeling complex ATPase gene Brm safeguards cell identity during directed cardiogenesis of mouse embryonic stem cells. Despite establishment of well-differentiated precardiac mesoderm, Brm-null cells predominantly became neural precursors, violating germ layer assignment. Trajectory inference showed sudden acquisition of non-mesodermal identity in Brm-null cells, consistent with a new transition state referred to as a saddle-node bifurcation. Mechanistically, loss of Brm prevented de novo accessibility of cardiac enhancers while increasing expression of neurogenic factor POU3F1, preventing expression of neural suppressor REST, and disrupting composition of BRG1 complexes. Brm mutant identity switch was overcome by increasing BMP4 levels during mesoderm induction. Mathematical modeling supports all our observations. In the mouse embryo, Brm deletion exacerbated mesoderm-deleted Brg1 mutant phenotypes, severely compromising cardiogenesis, unmasking an in vivo role for Brm. Our results reveal Brm as a compensable safeguard of the fidelity of mesoderm chromatin states, and support a model in which developmental canalization is not a rigid irreversible path, but a highly plastic trajectory.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Stem Cell

DISEASE(S): Cardiovascular System Disease

SUBMITTER: Ruth Huttenhain

LAB HEAD: Ruth Huttenhain

PROVIDER: PXD026638 | Pride | 2021-11-03

REPOSITORIES: Pride

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Brahma safeguards canalization of cardiac mesoderm differentiation.

Hota Swetansu K SK Rao Kavitha S KS Blair Andrew P AP Khalilimeybodi Ali A Hu Kevin M KM Thomas Reuben R So Kevin K Kameswaran Vasumathi V Xu Jiewei J Polacco Benjamin J BJ Desai Ravi V RV Chatterjee Nilanjana N Hsu Austin A Muncie Jonathon M JM Blotnick Aaron M AM Winchester Sarah A B SAB Weinberger Leor S LS Hüttenhain Ruth R Kathiriya Irfan S IS Krogan Nevan J NJ Saucerman Jeffrey J JJ Bruneau Benoit G BG

Nature 20220126 7895

Differentiation proceeds along a continuum of increasingly fate-restricted intermediates, referred to as canalization<sup>1,2</sup>. Canalization is essential for stabilizing cell fate, but the mechanisms that underlie robust canalization are unclear. Here we show that the BRG1/BRM-associated factor (BAF) chromatin-remodelling complex ATPase gene Brm safeguards cell identity during directed cardiogenesis of mouse embryonic stem cells. Despite the establishment of a well-differentiated precardiac ...[more]

PMID: 35082446

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Project description:The two catalytic subunits of the SWI/SNF chromatin remodeling complex - Brg1 and Brm - have been often implicated as essential components of common biological processes, suggesting a functional redundancy between these two proteins. For instance, earlier works indicated that both proteins are required for the activation of the myogenic program. However, their mutually exclusive pattern of incorporation in SWI/SNF complexes with variable composition and functional heterogeneity predicts that Brg1- and Brm-based SWI/SNF complexes execute specific functions to coordinate gene expression in multistep programs, such as skeletal myogenesis. We detected a distinct expression profile of Brg1 and Brm during the myogenic program, with Brm being upregulated in differentiating myocytes. Genetic knockdown of either Brg1 or Brm in skeletal myoblasts, followed by gene expression analysis, revealed discrete functions during myogenic differentiation. While Brm is required for the exit from the cell cycle at the early stages of differentiation, by repressing CyclinD1 transcription, Brg1 is required for the activation of muscle gene transcription. Interestingly, at later stages of differentiation Brg1 and Brm cooperate to the activation of a cluster of common target genes. Thus, Brg1 and Brm appear to coordinate activation and repression of distinct subsets of genes during initial phase myogenesis, and converge to cooperatively activate the expression of muscle genes at later stages. C2C12 myoblasts treated with siBRM or siBRG1 or siSCR in growth medium (GM) and differentiated by medium replacemnte (DM ). Celles were collected at 18h and 48h from the onset of DM for RNA extraction and microarray analysis. Arrays were used to generate 6 data sets in duplicate.To address the question of which genes were regulated by BRM and/or BRG1 the fold changes in gene expression were calculated between Scrambled siRNA and the BRM or BRG1 siRNA. The experiments were repeated at 2 different time points (18 hours and 48 hours) .

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