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Myocardin-related Transcription Factors Are Required for Skeletal Muscle Development

ABSTRACT: Myocardin-related transcription factors (MRTFs) play a central role in the regulation of actin expression and cytoskeletal dynamics. Stimuli that promote actin polymerization allow for shuttling of MRTFs to the nucleus where they activate serum response factor (SRF), a regulator of actin and other cytoskeletal protein genes. SRF is an essential regulator of skeletal muscle differentiation and numerous components of the muscle sarcomere, but the potential involvement of MRTFs in skeletal muscle development has not been examined. We explored the role of MRTFs in muscle development in vivo by generating mutant mice harboring a skeletal muscle-specific deletion of MRTF-B and a global deletion of MRTF-A. These double knockout (dKO) mice were able to form sarcomeres during embryogenesis. However, the sarcomeres were abnormally small and disorganized, causing skeletal muscle hypoplasia and perinatal lethality. Transcriptome analysis demonstrated dramatic dysregulation of actin genes in MRTF dKO mice, highlighting the importance of MRTFs in actin cycling and myofibrillogenesis. MRTFs were also necessary for the survival of skeletal myoblasts and for the efficient formation of intact myotubes. Our findings reveal a central role for MRTFs in sarcomere formation during skeletal muscle development and point to the potential involvement of these transcriptional coactivators in skeletal myopathies.

ORGANISM(S): Mus musculus

PROVIDER: GSE84063 | GEO | 2016/08/02

SECONDARY ACCESSION(S): PRJNA327918

REPOSITORIES: GEO

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Project description:Myocardin-related transcription factors (MRTFs) play a central role in the regulation of actin expression and cytoskeletal dynamics. Stimuli that promote actin polymerization allow for shuttling of MRTFs to the nucleus where they activate serum response factor (SRF), a regulator of actin and other cytoskeletal protein genes. SRF is an essential regulator of skeletal muscle differentiation and numerous components of the muscle sarcomere, but the potential involvement of MRTFs in skeletal muscle development has not been examined. We explored the role of MRTFs in muscle development in vivo by generating mutant mice harboring a skeletal muscle-specific deletion of MRTF-B and a global deletion of MRTF-A. These double knockout (dKO) mice were able to form sarcomeres during embryogenesis. However, the sarcomeres were abnormally small and disorganized, causing skeletal muscle hypoplasia and perinatal lethality. Transcriptome analysis demonstrated dramatic dysregulation of actin genes in MRTF dKO mice, highlighting the importance of MRTFs in actin cycling and myofibrillogenesis. MRTFs were also necessary for the survival of skeletal myoblasts and for the efficient formation of intact myotubes. Our findings reveal a central role for MRTFs in sarcomere formation during skeletal muscle development and point to the potential involvement of these transcriptional coactivators in skeletal myopathies. Gene expression profile was generated comparing wild type (WT) and HSA-Cre, MRTF-A/B double knockout mice, by deep seqencing, with three biological replicates, using Illumina HiSeq 2500.

2016-08-02 | E-GEOD-84063 | biostudies-arrayexpress

Project description:Myocardin-Related Transcription Factors A and B (MRTF-A and MRTF-B) are highly homologous proteins that function as powerful coactivators of serum response factor (SRF), a ubiquitously expressed transcription factor essential for cardiac development. The SRF/MRTF complex binds to CArG boxes found in the control regions of genes that regulate cytoskeletal dynamics and muscle contraction, among other processes. While SRF is required for heart development and function, the role of MRTFs in the developing or adult heart has not been explored. Through cardiac-specific deletion of MRTF alleles in mice, we show that either MRTF-A or MRTF-B is dispensable for cardiac development and function, whereas deletion of both MRTF-A and MRTF-B causes a spectrum of structural and functional cardiac abnormalities. Defects observed in MRTF-A/B null mice ranged from reduced cardiac contractility and adult onset heart failure to neonatal lethality accompanied by sarcomere disarray. RNA-seq analysis on neonatal hearts identified the most altered pathways in MRTF double knockout hearts as being involved in cytoskeletal organization. Together, these findings demonstrate redundant but essential roles of the MRTFs in maintenance of cardiac structure and function and as indispensible links in cardiac cytoskeletal gene regulatory networks.

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Definition of the fibroblast SRF-mediated immediate-early transcriptional response

Project description:To control transcription, SRF recruits signal-regulated co-activators, the Ternary Complex Factors (TCFs) and the Myocardin-related Transcription Factors (MRTFs), which compete for a common site on its DNA-binding domain. The TCFs - SAP-1, Elk-1 and Net - are Ets proteins that link SRF activity to Ras-ERK signalling. In contrast, the two MRTFs, MRTF-A and MRTF-B, link SRF activity to Rho-actin signalling. In this novel signalling pathway, the actin-binding MRTF RPEL domain acts as a G-actin sensor, controlling MRTF nuclear accumulation in response to signal-induced depletion of the G-actin pool. Previous studies have suggested that the Ras-ERK signalling and Rho-actin pathways control specific subsets of SRF target genes. We used ChIP-seq and RNA-seq to analyse the immediate-early transcriptional response in NIH3T3 fibroblasts, using pathway-specific inhibitors to identify the contributions of Ras-ERK and Rho-actin signalling Chromatin immunoprecipitation and sequencing (ChIP-seq) in NIH3T3 fibroblast after serum stimulation in presence or absence of LatrunculinB or U0126 drugs and using antibodies against SRF, MRTF-A, MRTF-B, SAP1, ELK1, NET, Pol II, PolII S5P, PolII S2P and total H3. Validation by ChIP-PCR. Strand specific total-RNA-seq following DSN normalisation and validation by qRT-PCR from NIH3T3 stimulated by serum or Cytochalasin D in presence or absence of LatrunculinB and/or U0126 drugs.

2014-04-24 | E-GEOD-45888 | biostudies-arrayexpress

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CCG-1423-derived compounds reduce global RNA synthesis and inhibit transcriptional responses (PRO-seq)

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CCG-1423-derived compounds reduce global RNA synthesis and inhibit transcriptional responses (ChIP-seq)

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Myopalladin promotes muscle growth through modulation of the serum response factor pathway

Project description:Myopalladin (MYPN) is a striated muscle-specific protein located in the Z-line and I-band of the sarcomere as well as the nucleus. Analysis of MYPN knockout (MKO) mice showed a 48% reduction in myofiber cross-sectional area in MKO mice and a consequent reduction in isometric force generation and power output. Similarly, reduced myotube width was observed in MKO primary myoblast cultures. RNA-Seq studies revealed downregulation of serum response factor (SRF)-target genes in MKO mice, important for muscle growth and differentiation, and further studies revealed that MYPN, like its homologue PALLD, can bind and bundle filamentous actin as well as interact with MRTF-A, both major players in the regulation of the SRF pathway. Consistently, MYPN increased MRTF-A-mediated activation of SRF signaling in myogenic cells, and transduction of MKO myoblasts with constitutive active SRF rescued the reduced myotube width, demonstrating that MYPN promotes skeletal muscle growth through activation of the SRF pathway.

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MRTF-SRF signalling in the T cell IL2 response

Project description:The transcription factor SRF is a master regulator of growth factor inducible and cytoskeletal gene expression. Two transcription cofactor families, the TCFs & the MRTFs, are responsible for SRF's activity to direct transcriptional programme in response to extracellular signalling through the Ras-ERK and Rho-actin pathways respectively. We are investigating the role of the SRF network in the response to infection, using the Listeria monocytogenes model. We find that inactivation of the network impairs the ability of CD8 T cells to proliferate in response to listeria and to generate memory cells. Surprisingly, the defect reflects impaired MRTF-SRF signalling rather than the TCF-SRF signalling pathway usually associated with proliferation. Moreover, the defec doesn'tt lie downstream of the initial activation of the TCR, appearing instead to arise from an inability of CD8 T cells to present IL-2 to each other in paracrine fashion. Consistent with these observations, we find that while cultured CD8 MRTF-null T cells can be effectively activated by TCR crosslinking invitro, their ability to form clusters, which is IL-2-dependent, is impaired. Moreover, as expected, pilot experiments indicate that these cells exhibit deficits both in the basal levels of MRTF-SRF target gene expression, and in their ability to induce these genes in response to IL-2 stimulation:

2023-10-23 | GSE241689 | GEO

Lap2α is required for MRTF-A-SRF transcriptional activity [ChIP-seq]

Project description:Myocardin-related transcription factor A (MRTF-A) in complex with the serum response factor (SRF) regulates the expression of cytoskeletal genes in response to cytoplasmic and nuclear actin dynamics. Different components of nucleoskeleton, besides nuclear actin, also regulate the activity of MRTF-A. Here we extend these studies by showing that lamina-associated polypeptide 2α (Lap2α), the nucleoplasmic isoform of Lap2, is a novel regulator, and a direct binding partner of MRTF-A. Lap2α is a nucleoplasmic protein that interacts with A-type lamins and the retinoblastoma protein (pRb) and contributes to chromatin organization. Unlike other known MRTF-A regulators, Lap2α is not required for MRTF-A nucleo-cytoplasmic shuttling; it functions within the nucleus where it binds MRTF-A directly via its unique C-terminal domain prior to MRTF-A forming the complex with chromatin and SRF. Such interaction affects MRTF-A transcriptional activity since genome-wide analysis revealed reduced binding of MRTF-A to SRF target genes in Lap2α knockout cells compared to control cells that consequently led to impaired expression of target genes. Our studies therefore add another regulatory layer to the control MRTF-A-SRF-mediated gene expression, and broaden the role of Lap2α in transcriptional regulation.

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