Project description:We report the application of single myofiber ATAC-Seq (smfATAC-Seq) to investigate the chromatin accessibility of a single myofiber without the presence of confounding muscle resident cell types. This method demonstrates that open chromatin regions of myonuclei can be tagmentated and high-quality sequencing ready libraries can be generated from these fragments. To perform comparative analysis as well as to demonstrate the applicability of the smfATAC-Sew to study changes in chromatin of myonuclei within different contexts, smfATAC-Seq was performed both on uninjured myofibers as well as injured myofibers seven days after induced injury. Furthermore, ATAC-Seq on 5000 muscle stem cells (MuSCs) was also performed according to the previously described OMNI ATAC-Seq protocol (Corces, M.R. et al. Nature Methods, 2017) in order to compare the sequencing quality of the smfATAC-Seq as well as to demonstrate the changes in open chromatin that occur from the stem cell state to the fully differentiated myofibers. smfATAC-seq resulted in comparable coverage and sequencing depth to the ATAC-seq performed on MuSCs and allowed for peak calling and differential peak analysis. These analysis revealed that the open chromatin state of uninjured and injured myofibers after seven days are mostly similar although some regions invovled in immune response remain in an open state in the injured myofibers compared to the uninjured myofibers and the regions involved in structural formation of the muscle are more accessible in the case of regeneration. Even though certain differences in the open chromatin are observed, smfATAC-Seq analysis suggest that overall, the open chromatin state of the myonuclei returns back to homeostasis after seven days of regeneration. Furthermore, smfATAC-Seq comparison with the ATAC-Seq from MuSCs show the differences in open chromatin regions between these conditions. Increased accessibility of genes involved in myogenesis and structural components can be observed in the myofibers compared to MuSCs while MuSCs show increased accessibility in regions involved in membrane permeability and signalling pathways. In addition, the regions that are accessible for both conditions include genes involved in mitochondrial transport, regulation of transcription and regulation of metabolites and energy. Overall, this study introduces smfATAC-Seq that succesfully assesses the genome-wide chromatin accessibility of a single myofiber with relatively high sequencing depth. The smfATAC-Seq can be used to perform comparative analysis between different conditions such as injury. However, this method can be readily applied to study differences between young and old myofibers or in the context of muscular dystrophy, cachexia, and exercise.
Project description:The maintenance of cell lineage and cell fate are essential for the function of adult stem cells. Despite this, the epigenetic mechanisms that regulate muscle stem cell (MuSC) identity are not well understood. In this study, we performed Cut&Tag of the activating histone marks H3K4me3 and H3K27ac on freshly isolated quiescent MuSCs and found that a large number of genes without transcription still maintained the permissive mark H3K4me3 but lacked the marker of active enhancers, H3K27ac. These genes included those that are essential for non-myogenic lineage determination. We found that many of the genes that were not transcribed but enriched for H3K4me3, were also enriched for the RE-1 binding motif, the motif recognized by the repressive transcription factor REST. Using a genetic mouse model where REST is conditionally knocked out of MuSCs, we further investigated the role of REST in the maintenance of quiescent MuSC cell identity. Investigation of the transcriptome and chromatin accessibility of WT and REST deficient MuSCs determined that the loss of REST results in the gain of expression of key genes of several non-myogenic tissues, particularly neuronal genes. Additionally, the loss of REST led to the dramatic reduction of the MuSC pool and the induction of muscle atrophy. The unstable cell identity caused by the genetic deletion of REST results in the MuSCs undergoing apoptosis and is the main driver of the observed loss of the MuSC pool. Together, the data presented in this study establishes a novel function of the transcription factor REST, where it safeguards the identity and myogenic lineage of MuSCs, through the repression of alternative lineages.
Project description:The maintenance of cell lineage and cell fate are essential for the function of adult stem cells. Despite this, the epigenetic mechanisms that regulate muscle stem cell (MuSC) identity are not well understood. In this study, we performed Cut&Tag of the activating histone marks H3K4me3 and H3K27ac on freshly isolated quiescent MuSCs and found that a large number of genes without transcription still maintained the permissive mark H3K4me3 but lacked the marker of active enhancers, H3K27ac. These genes included those that are essential for non-myogenic lineage determination. We found that many of the genes that were not transcribed but enriched for H3K4me3, were also enriched for the RE-1 binding motif, the motif recognized by the repressive transcription factor REST. Using a genetic mouse model where REST is conditionally knocked out of MuSCs, we further investigated the role of REST in the maintenance of quiescent MuSC cell identity. Investigation of the transcriptome and chromatin accessibility of WT and REST deficient MuSCs determined that the loss of REST results in the gain of expression of key genes of several non-myogenic tissues, particularly neuronal genes. Additionally, the loss of REST led to the dramatic reduction of the MuSC pool and the induction of muscle atrophy. The unstable cell identity caused by the genetic deletion of REST results in the MuSCs undergoing apoptosis and is the main driver of the observed loss of the MuSC pool. Together, the data presented in this study establishes a novel function of the transcription factor REST, where it safeguards the identity and myogenic lineage of MuSCs, through the repression of alternative lineages.
Project description:MicroRNA-expression profile of dystrophic single fibres vs wild type single fibers isolated from different muscle of mdx and c57bl mice. Myofibers were isolated from different muscle type (tibialis, diaphragm and quadriceps of gender- (male) and age- (3 month old and half) matched wt and dystrophic mice). 9 total samples per animal model, 3 replicates per muscle type sample
Project description:MicroRNA-expression profile of dystrophic single fibers compared to wild type single fibers isolated from different muscles of mdx and C57BL mice. Myofibers were isolated from different muscle types (tibialis, diaphragm and quadriceps) of gender- (male) and age- (3 month old and half) matched wt and dystrophic mice. 9 total samples per animal model (C57BL, mdx), 3 replicates per muscle type.
Project description:MicroRNA-expression profile of dystrophic single fibres vs wild type single fibers isolated from different muscle of mdx and c57bl mice. Myofibers were isolated from different muscle type (tibialis, diaphragm and quadriceps of gender- (male) and age- (3 month old and half) matched wt and dystrophic mice).