The BAF60c-MyoD complex poises chromatin for rapid transcription

Journal of Biological Chemistry, 2001

Cell cycle arrest is critical for muscle differentiation, and the two processes are closely coordinated but temporally separable. SWI/SNF complexes are ATP-dependent chromatin-remodeling enzymes that have been shown to be required for muscle differentiation in cell culture and have also been reported to be required for Rb-mediated cell cycle arrest. We therefore looked more closely at how SWI/SNF enzymes affect the events that occur during MyoD-induced myogenesis, namely, cell cycle regulation and muscle-specific gene expression, in cells that inducibly express dominant negative versions of Brahma (BRM) and Brahma-related gene 1 (BRG1), the ATPase subunits of two distinct SWI/SNF complexes. Although dominant negative BRM and BRG1 inhibited expression of every muscle-specific regulator and structural gene assayed, there was no effect on MyoD-induced activation of cell cycle regulatory proteins, and thus, cells arrested normally. In particular, in the presence or absence of dominant negative BRM or BRG1, MyoD was able to activate expression of p21, cyclin D3, and Rb, all of which are critical for cell cycle withdrawal in the G 1 /G 0 phase of the cell cycle. These findings suggest that at least one basis for the distinct mechanisms that regulate cessation of cell proliferation and musclespecific gene expression during muscle differentiation is that SWI/SNF-mediated chromatin-remodeling enzymes are required only for the latter.

Developmental Dynamics, 2014

Background: Among the complexities of skeletal muscle differentiation is a temporal distinction in the onset of expression of different lineage‐specific genes. The lineage‐determining factor MyoD is bound to myogenic genes at the onset of differentiation whether gene activation is immediate or delayed. How temporal regulation of differentiation‐specific genes is established remains unclear. Results: Using embryonic tissue, we addressed the molecular differences in the organization of the myogenin and muscle creatine kinase (MCK) gene promoters by examining regulatory factor binding as a function of both time and spatial organization during somitogenesis. At the myogenin promoter, binding of the homeodomain factor Pbx1 coincided with H3 hyperacetylation and was followed by binding of co‐activators that modulate chromatin structure. MyoD and myogenin binding occurred subsequently, demonstrating that Pbx1 facilitates chromatin remodeling and modification before myogenic regulatory fact...

Frontiers in Genetics, 2020

Cellular commitment and differentiation involve highly coordinated mechanisms by which tissue-specific genes are activated while others are repressed. These mechanisms rely on the activity of specific transcription factors, chromatin remodeling enzymes, and higherorder chromatin organization in order to modulate transcriptional regulation on multiple cellular contexts. Tissue-specific transcription factors are key mediators of cell fate specification with the ability to reprogram cell types into different lineages. A classic example of a master transcription factor is the muscle specific factor MyoD, which belongs to the family of myogenic regulatory factors (MRFs). MRFs regulate cell fate determination and terminal differentiation of the myogenic precursors in a multistep process that eventually culminate with formation of muscle fibers. This developmental progression involves the activation and proliferation of muscle stem cells, commitment, and cell cycle exit and fusion of mononucleated myoblast to generate myotubes and myofibers. Although the epigenetics of muscle regeneration has been extensively addressed and discussed over the recent years, the influence of higher-order chromatin organization in skeletal muscle regeneration is still a field of development. In this review, we will focus on the epigenetic mechanisms modulating muscle gene expression and on the incipient work that addresses three-dimensional genome architecture and its influence in cell fate determination and differentiation to achieve skeletal myogenesis. We will visit known alterations of genome organization mediated by chromosomal fusions giving rise to novel regulatory landscapes, enhancing oncogenic activation in muscle, such as alveolar rhabdomyosarcomas (ARMS).

Oncogene, 2003

The conversion of skeletal myoblasts to terminally differentiated myocytes is negatively controlled by several growth factors and oncoproteins. In this study, we have investigated the molecular mechanisms by which v-Src, a prototypic tyrosine kinase, perturbs myogenesis in primary avian myoblasts and in established murine C2C12 satellite cells. We determined the expression levels of the cell cycle regulators pRb, cyclin D1 and D3 and cyclindependent kinase inhibitors p21 and p27 in v-Srctransformed myoblasts and found that, in contrast to myogenin, they are normally modulated by differentiative cues, implying that v-Src affects myogenesis independent of cell proliferation. We then examined the levels of expression, DNA-binding ability and transcription-activation potentials of myogenic regulatory factors in transformed myoblasts and in myotubes after reactivation of a temperature-sensitive allele of v-Src. Our results reveal two distinct potential modes of repression targeted to myogenic factors. On the one hand, we show that v-Src reversibly inhibits the expression of MyoD and myogenin in C2C12 cells and of myogenin in quail myoblasts. Remarkably, these loci become resistant to activation of the kinase in the postmitotic compartment. On the other hand, we demonstrate that v-Src efficiently inhibits muscle gene expression by repressing the transcriptional activity of myogenic factors without affecting MyoD DNAbinding activity. Indeed, forced expression of MyoD and myogenin allows terminal differentiation of transformed myoblasts. Finally, we found that ectopic expression of the coactivator p300 restores transcription from extrachromosomal muscle-specific promoters.

Nature Genetics, 2004

During skeletal myogenesis, genomic reprogramming toward terminal differentiation is achieved by recruiting chromatin-modifying enzymes to muscle-specific loci. The relative contribution of extracellular signaling cascades in targeting these enzymes to individual genes is unknown. Here we show that the differentiation-activated p38 pathway targets the SWI-SNF chromatin-remodeling complex to myogenic loci. Upon differentiation, p38 kinases were recruited to the chromatin of muscle-regulatory elements. Blockade of p38 alpha/beta repressed the transcription of muscle genes by preventing recruitment of the SWI-SNF complex at these elements without affecting chromatin binding of muscle-regulatory factors and acetyltransferases. The SWI-SNF subunit BAF60 could be phosphorylated by p38 alpha-beta in vitro, and forced activation of p38 alpha/beta in myoblasts by expression of a constitutively active MKK6 (refs. 5,6,7) promoted unscheduled SWI-SNF recruitment to the myogenin promoter. Conversely, inactivation of SWI-SNF enzymatic subunits abrogated MKK6-dependent induction of muscle gene expression. These results identify an unexpected function of differentiation-activated p38 in converting external cues into chromatin modifications at discrete loci, by selectively targeting SWI-SNF to muscle-regulatory elements.

Nucleic acids research, 2015

During skeletal muscle differentiation, the activation of some tissue-specific genes occurs immediately while others are delayed. The molecular basis controlling temporal gene regulation is poorly understood. We show that the regulatory sequences, but not other regions of genes expressed at late times of myogenesis, are in close physical proximity in differentiating embryonic tissue and in differentiating culture cells, despite these genes being located on different chromosomes. Formation of these inter-chromosomal interactions requires the lineage-determinant MyoD and functional Brg1, the ATPase subunit of SWI/SNF chromatin remodeling enzymes. Ectopic expression of myogenin and a specific Mef2 isoform induced myogenic differentiation without activating endogenous MyoD expression. Under these conditions, the regulatory sequences of late gene loci were not in close proximity, and these genes were prematurely activated. The data indicate that the spatial organization of late genes con...

Skeletal Muscle

Background The AP-1 transcription factor, FBJ osteosarcoma oncogene (FOS), is induced in adult muscle satellite cells (SCs) within hours following muscle damage and is required for effective stem cell activation and muscle repair. However, why FOS is rapidly downregulated before SCs enter cell cycle as progenitor cells (i.e., transiently expressed) remains unclear. Further, whether boosting FOS levels in the proliferating progeny of SCs can enhance their myogenic properties needs further evaluation. Methods We established an inducible, FOS expression system to evaluate the impact of persistent FOS activity in muscle progenitor cells ex vivo. We performed various assays to measure cellular proliferation and differentiation, as well as uncover changes in RNA levels and three-dimensional (3D) chromatin interactions. Results Persistent FOS activity in primary muscle progenitor cells severely antagonizes their ability to differentiate and form myotubes within the first 2 weeks in culture...

Journal of Biological Chemistry, 1997

Nucleic Acids Research, 2012

The bHLH transcription factor MyoD, the prototypical master regulator of differentiation, directs a complex program of gene expression during skeletal myogenesis. The up-regulation of the cdk inhibitor p57 kip2 plays a critical role in coordinating differentiation and growth arrest during muscle development, as well as in other tissues. p57 kip2 displays a highly specific expression pattern and is subject to a complex epigenetic control driving the imprinting of the paternal allele. However, the regulatory mechanisms governing its expression during development are still poorly understood. We have identified an unexpected mechanism by which MyoD regulates p57 kip2 transcription in differentiating muscle cells. We show that the induction of p57 kip2 requires MyoD binding to a long-distance element located within the imprinting control region KvDMR1 and the consequent release of a chromatin loop involving p57 kip2 promoter. We also show that differentiation-dependent regulation of p57 kip2 , while involving a region implicated in the imprinting process, is distinct and hierarchically subordinated to the imprinting control. These findings highlight a novel mechanism, involving the modification of higher order chromatin structures, by which MyoD regulates gene expression. Our results also suggest that chromatin folding mediated by KvDMR1 could account for the highly restricted expression of p57 kip2 during development and, possibly, for its aberrant silencing in some pathologies.

Development, 2014

Higher-order chromatin structures appear to be dynamically arranged during development and differentiation. However, the molecular mechanism underlying their maintenance or disruption and their functional relevance to gene regulation are poorly understood. We recently described a dynamic long-range chromatin interaction between the gene promoter of the cdk inhibitor p57 kip2 (also known as Cdkn1c) and the imprinting control region KvDMR1 in muscle cells. Here, we show that CTCF, the best characterized organizer of long-range chromatin interactions, binds to both the p57 kip2 promoter and KvDMR1 and is necessary for the maintenance of their physical contact. Moreover, we show that CTCF-mediated looping is required to prevent p57 kip2 expression before differentiation. Finally, we provide evidence that the induction of p57 kip2 during myogenesis involves the physical interaction of the muscle-regulatory factor MyoD with CTCF at KvDMR1, the displacement of the cohesin complex subunit Rad21 and the destabilization of the chromatin loop. The finding that MyoD affects chromatin looping at CTCF-binding sites represents the first evidence that a differentiation factor regulates chromatin-loop dynamics and provides a useful paradigm for gaining insights into the developmental regulation of long-range chromatin contacts.

The EMBO Journal, 2010

The chromatin-remodelling complex SNF2-related CBP activator protein (SRCAP) regulates chromatin structure in yeast by modulating the exchange of histone H2A for the H2A.Z variant. Here, we have investigated the contribution of H2A.Z-mediated chromatin remodelling to mammalian cell differentiation reprogramming. We show that the SRCAP subunit named ZNHIT1 or p18 Hamlet , which is a substrate of p38 MAPK, is recruited to the myogenin promoter at the onset of muscle differentiation, in a p38 MAPK-dependent manner. We also show that p18 Hamlet is required for H2A.Z accumulation into this genomic region and for subsequent muscle gene transcriptional activation. Accordingly, downregulation of several subunits or the SRCAP complex impairs muscle gene expression. These results identify SRCAP/H2A.Z-mediated chromatin remodelling as a key early event in muscle differentiation-specific gene expression. We also propose a mechanism by which p38 MAPK-mediated signals are converted into chromatin structural changes, thereby facilitating transcriptional activation during mammalian cell differentiation.

The EMBO Journal, 2001

The molecular mechanism(s) that are responsible for suppressing MyoD's transcriptional activities in undifferentiated skeletal muscle cells have not yet been determined. We now show that MyoD associates with a histone deacetylase-1 (HDAC1) in these cells and that this interaction is responsible for silencing MyoDdependent transcription of endogenous p21 as well as muscle-speci®c genes. Speci®cally, we present evidence that HDAC1 can bind directly to MyoD and use an acetylated MyoD as a substrate in vitro, whereas a mutant version of HDAC1 (H141A) can not. Furthermore, this mutant also fails to repress MyoD-mediated transcription in vivo, and unlike wild-type HDAC1 it can not inhibit myogenic conversion, as judged by confocal microscopy. Finally, we show that an endogenous MyoD can be acetylated upon its conversion to a hypophosphorylated state and only when the cells have been induced to differentiate. These results provide for a model which postulates that MyoD may be co-dependent on HDAC1 and P/CAF for temporally controlling its transcriptional activity before and after the differentiation of muscle cells.

Molecular and Cellular Biology, 2003

PLoS ONE, 2013

Heterochromatin protein 1 (HP1) is an essential heterochromatin-associated protein typically involved in the epigenetic regulation of gene silencing. However, recent reports have demonstrated that HP1 can also activate gene expression in certain contexts including differentiation. To explore the role of each of the three mammalian HP1 family members (a, b and c) in skeletal muscle, their expression was individually disrupted in differentiating skeletal myocytes. Among the three isoforms of HP1, HP1a was specifically required for myogenic gene expression in myoblasts only. Knockdown of HP1a led to a defect in transcription of skeletal muscle-specific genes including Lbx1, MyoD and myogenin. HP1a binds to the genomic region of myogenic genes and depletion of HP1a results in a paradoxical increase in histone H3 lysine 9 trimethylation (H3K9me3) at these sites. JHDM3A, a H3K9 demethylase also binds to myogenic gene's genomic regions in myoblasts in a HP1a-dependent manner. JHDM3A interacts with HP1a and knockdown of JHDM3A in myoblasts recapitulates the decreased myogenic gene transcription seen with HP1a depletion. These results propose a novel mechanism for HP1adependent gene activation by interacting with the demethylase JHDM3A and that HP1a is required for maintenance of myogenic gene expression in myoblasts.

… and cellular biology, 2006

The MyoD family of basic helix-loop-helix transcription factors function as heterodimers with members of the E-protein family to induce myogenic gene activation. The E-protein HEB is alternatively spliced to generate ␣ and ␤ isoforms. While the function of these molecules has been studied in other cell types, questions persist regarding the molecular functions of HEB proteins in skeletal muscle. Our data demonstrate that HEB␣ expression remains unchanged in both myoblasts and myotubes, whereas HEB␤ is upregulated during the early phases of terminal differentiation. Upon induction of differentiation, a MyoD-HEB␤ complex bound the E1 E-box of the myogenin promoter leading to transcriptional activation. Importantly, forced expression of HEB␤ with MyoD synergistically lead to precocious myogenin expression in proliferating myoblasts. However, after differentiation, HEB␣ and HEB␤ synergized with myogenin, but not MyoD, to activate the myogenin promoter. Specific knockdown of HEB␤ by small interfering RNA in myoblasts blocked differentiation and inhibited induction of myogenin transcription. Therefore, HEB␣ and HEB␤ play novel and central roles in orchestrating the regulation of myogenic factor activity through myogenic differentiation.