Project description:Skeletal muscle stem cells, or satellite cells (SCs), are essential to regenerate and maintain muscle. Quiescent SCs reside in an asymmetric niche between the basal lamina and myofiber membrane. To repair muscle, SCs activate, proliferate, and differentiate, fusing to repair myofibers or reacquiring quiescence to replenish the SC niche. Little is known about when SCs reacquire quiescence during regeneration or the cellular processes that direct SC fate decisions and progression through myogenesis. Single cell sequencing of myogenic cells in regenerating muscle identifies SCs reacquiring quiescence and reveals that non-cell autonomous signaling networks influence SC fate decisions during regeneration. Single cell RNA-sequencing of regenerating skeletal muscle reveals that RBP expression, including numerous neuromuscular disease-associated RBPs, is temporally regulated in skeletal muscle stem cells and correlates to stages of myogenic differentiation. By combining machine learning with RBP engagement scoring, we discover that the neuromuscular disease associated RBP Hnrnpa2b1 is a differentiation-specifying regulator of myogenesis controlling myogenic cell fate transitions during terminal differentiation.
Project description:Functional crosstalk between histone modifications and chromatin remodeling has emerged as a key regulatory mode of transcriptional control during cell fate decisions, but the underlying mechanisms are not fully understood. Here we demonstrate that HRP2-DPF3a-BAF complex coordinates histone H3 lysine 36 methylation (H3K36me) and ATP-dependent chromatin remodeling to regulate chromatin dynamic and gene transcription during myogenic differentiation. Mechanistically, through its HIV integrase binding domain (IBD), HRP2 associates with BRG1/BRM associated factor (BAF) chromatin remodeling complex by direct interaction with BAF45c (DPF3a) subunit. Through its Pro-Trp-Trp-Pro (PWWP) domain, HRP2 preferentially binds to H3K36me2. Integrative transcriptomic and cistromic analyses, coupled with ATAC-seq, reveal that HRP2 and DPF3a activate myogenic genes by increasing chromatin accessibility through recruitment of BRG1, the ATPase subunit of the BAF complex.
Project description:RNA-binding proteins (RBPs) are essential for skeletal muscle regeneration and RBP dysfunction causes muscle degeneration and neuromuscular disease (NMD). How the timing of RBP function governs the complex cell fate decisions during muscle regeneration is poorly understood. Here, single cell analysis of skeletal muscle regeneration reveals the timing of NMD-associated RBPs expression in muscle progenitors, including a massive upregulation of Hnrnpa2b1 (A2b1). A2b1 promotes muscle progenitor plasticity by regulating the splicing of RNAs expressed at specific times during the trajectory of muscle differentiation. Using RBP-RNA engagement scoring and machine learning, we accurately predict NMD-associated RBP functionality in directing myogenesis. Together our analysis reveals how A2b1 regulates myogenic plasticity and provides a broadly applicable single cell methodology for examining how RBPs influence complex cell fate trajectories.
Project description:Functional crosstalk between histone modifications and chromatin remodeling has emerged as a key regulatory mode of transcriptional control during cell fate decisions, but the underlying mechanisms are not fully understood. Here we demonstrate that HRP2-DPF3a-BAF complex coordinates histone H3 lysine 36 methylation (H3K36me) and ATP-dependent chromatin remodeling to regulate chromatin dynamic and gene transcription during myogenic differentiation. Mechanistically, through its HIV integrase binding domain (IBD), HRP2 associates with BRG1/BRM associated factor (BAF) chromatin remodeling complex by direct interaction with BAF45c (DPF3a) subunit. Through its Pro-Trp-Trp-Pro (PWWP) domain, HRP2 preferentially binds to H3K36me2. Consistent with the biochemical studies, genome-wide analyses show that HRP2 colocalizes with DPF3a at gene promoters enriched for H3K36me2.
Project description:Direct lineage reprogramming provides a unique system to study cell fate transitions and unearth molecular mechanisms that safeguard cellular identity. We previously reported on direct conversion of mouse fibroblasts into induced myogenic progenitor cells (iMPCs) by transient MyoD overexpression in concert with small molecules treatment. Here we employed integrative multi-omic approaches to delineate the molecular landscape of fibroblast reprogramming into iMPCs in comparison to transdifferentiation into myogenic cells solely by MyoD overexpression. Utilizing bulk RNA-sequencing and mass spectrometry, we uncovered molecular regulators and pathways that endow a myogenic stem cell identity on fibroblasts only in the presence of small molecule treatment. In addition, we demonstrate that Pax7+ cells in iMPCs share molecular attributes with myoblasts, however in addition express unique genes, proteins and pathways that are indicative of a more activated satellite cell-like state in vitro. Collectively, this study charts a molecular blueprint for reprogramming fibroblasts into muscle stem and progenitor cells and further establishes the fidelity of stable iMPC cultures in capturing skeletal muscle regeneration in vitro for disease modeling and basic research applications.
Project description:Notch signalling plays crucial roles in mediating cell fate choices in all metazoans largely by specifying the transcriptional output of one cell in response to a neighbouring cell. The DNA-binding protein RBPJ is the principle effector of this pathway in mammals and together with the transcription factor moiety of Notch (NICD) it regulates the expression of target genes. The prevalent view presumes that RBPJ statically occupies consensus binding sites while exchanging repressors for activators in response to NICD. We present the first specific RBPJ chromatin immunoprecipitation and high-throughput sequencing study in mammalian cells. To dissect the mode of transcriptional regulation by RBPJ and identify its direct targets, whole genome binding profiles were generated for RBPJ, its coactivator p300, NICD and the histone H3 modifications H3K4me3, H3K4me1 and H3K27ac in myogenic cells under active or inhibitory Notch signalling conditions. Our results demonstrate dynamic binding of RBPJ in response to Notch activation at essentially all sites co-occupied by NICD. Additionally, we identify a distinct set of sites where RBPJ recruits neither NICD nor p300, and binds DNA statically, irrespective of Notch activity. These findings significantly modify our views on how RBPJ and Notch signalling mediate their activities and consequently impact on cell fate decisions.
Project description:Notch signalling plays crucial roles in mediating cell fate choices in all metazoans largely by specifying the transcriptional output of one cell in response to a neighbouring cell. The DNA-binding protein RBPJ is the principle effector of this pathway in mammals and together with the transcription factor moiety of Notch (NICD) it regulates the expression of target genes. The prevalent view presumes that RBPJ statically occupies consensus binding sites while exchanging repressors for activators in response to NICD. We present the first specific RBPJ chromatin immunoprecipitation and high-throughput sequencing study in mammalian cells. To dissect the mode of transcriptional regulation by RBPJ and identify its direct targets, whole genome binding profiles were generated for RBPJ, its coactivator p300, NICD and the histone H3 modifications H3K4me3, H3K4me1 and H3K27ac in myogenic cells under active or inhibitory Notch signalling conditions. Our results demonstrate dynamic binding of RBPJ in response to Notch activation at essentially all sites co-occupied by NICD. Additionally, we identify a distinct set of sites where RBPJ recruits neither NICD nor p300, and binds DNA statically, irrespective of Notch activity. These findings significantly modify our views on how RBPJ and Notch signalling mediate their activities and consequently impact on cell fate decisions. ChIP (chromatin immunoprecipitation) is followed by deep sequencing to generate genome-wide patterns of RBP-J binding in mouse C2C12 cells under various conditions. Cells were either Notch activated by exposure to immobilized ligand or by overexpression of NICDGFP, or Notch inhibited by treatment with DAPT. Notch activation and inhibition treatments were applied for 6h and 24h. In addition to RBP-J, p300 and NICDGFP were profiled by ChIP-Seq and gene expression was assessed by RNA-Seq.
Project description:Fate decisions in the embryo are controlled by a plethora of microenvironmental interactions in a three-dimensional niche. To investigate whether aspects of this microenvironmental complexity can be engineered to direct myogenic human induced pluripotent stem cell (hiPSC) differentiation, we screened cell types present in the developmental or adult stem cell niche in heterotypic suspension embryoids. We identified embryonic endothelial cells and fibroblasts as highly permissive for myogenic specification of hiPSCs. After two weeks of sequential Wnt and FGF pathway induction, these three-component embryoids (iTCEs) are enriched in Pax7 positive embryonic-like myogenic progenitors (eMPs) that can be isolated by flow cytometry. Myogenic differentiation of hiPSCs in iTCEs relies on a specialized structural microenvironment and depends on MAPK, PI3K/AKT, and Notch signaling. After transplantation in a mouse model of Duchenne muscular dystrophy, eMPs repopulate the stem cell niche, reactivate after repeated injury and, compared to adult human myoblasts, display enhanced fusion and lead to stronger muscles. Altogether, we provide a two-week protocol for efficient and scalable suspension-based 3D derivation of Pax7 positive myogenic progenitors from hiPSCs.