RESUMEN
The function and maintenance of muscle stem cells (MuSCs) are tightly regulated by signals originating from their niche environment. Skeletal myofibers are a principle component of the MuSC niche and are in direct contact with the muscle stem cells. Here, we show that Myf6 establishes a ligand/receptor interaction between muscle stem cells and their associated muscle fibers. Our data show that Myf6 transcriptionally regulates a broad spectrum of myokines and muscle-secreted proteins in skeletal myofibers, including EGF. EGFR signaling blocks p38 MAP kinase-induced differentiation of muscle stem cells. Homozygous deletion of Myf6 causes a significant reduction in the ability of muscle to produce EGF, leading to a deregulation in EGFR signaling. Consequently, although Myf6-knockout mice are born with a normal muscle stem cell compartment, they undergo a progressive reduction in their stem cell pool during postnatal life due to spontaneous exit from quiescence. Taken together, our data uncover a novel role for Myf6 in promoting the expression of key myokines, such as EGF, in the muscle fiber which prevents muscle stem cell exhaustion by blocking their premature differentiation.
Asunto(s)
Factores Reguladores Miogénicos , Células Madre , Animales , Diferenciación Celular/genética , Homocigoto , Ratones , Músculo Esquelético , Factores Reguladores Miogénicos/genética , Eliminación de SecuenciaRESUMEN
Myogenic potential, survival and expansion of mammalian muscle progenitors depend on the myogenic determinants Pax3 and Pax7 embryonically, and Pax7 alone perinatally. Several in vitro studies support the critical role of Pax7 in these functions of adult muscle stem cells (satellite cells), but a formal demonstration has been lacking in vivo. Here we show, through the application of inducible Cre/loxP lineage tracing and conditional gene inactivation to the tibialis anterior muscle regeneration paradigm, that, unexpectedly, when Pax7 is inactivated in adult mice, mutant satellite cells are not compromised in muscle regeneration, they can proliferate and reoccupy the sublaminal satellite niche, and they are able to support further regenerative processes. Dual adult inactivation of Pax3 and Pax7 also results in normal muscle regeneration. Multiple time points of gene inactivation reveal that Pax7 is only required up to the juvenile period when progenitor cells make the transition into quiescence. Furthermore, we demonstrate a cell-intrinsic difference between neonatal progenitor and adult satellite cells in their Pax7-dependency. Our finding of an age-dependent change in the genetic requirement for muscle stem cells cautions against inferring adult stem-cell biology from embryonic studies, and has direct implications for the use of stem cells from hosts of different ages in transplantation-based therapy.
Asunto(s)
Regeneración/fisiología , Células Satélite del Músculo Esquelético/citología , Células Satélite del Músculo Esquelético/fisiología , Células Madre/citología , Células Madre/fisiología , Envejecimiento , Animales , Proliferación Celular , Células Cultivadas , Regulación del Desarrollo de la Expresión Génica , Ratones , Músculo Esquelético/citología , Músculo Esquelético/crecimiento & desarrollo , Mutación , Factor de Transcripción PAX3 , Factor de Transcripción PAX7/metabolismo , Factores de Transcripción Paired Box/metabolismo , Regeneración/genética , Células Satélite del Músculo Esquelético/efectos de los fármacos , Moduladores Selectivos de los Receptores de Estrógeno/farmacología , Células Madre/efectos de los fármacos , Tamoxifeno/farmacología , Factores de TiempoRESUMEN
Myostatin and activin A are structurally related secreted proteins that act to limit skeletal muscle growth. The cellular targets for myostatin and activin A in muscle and the role of satellite cells in mediating muscle hypertrophy induced by inhibition of this signaling pathway have not been fully elucidated. Here we show that myostatin/activin A inhibition can cause muscle hypertrophy in mice lacking either syndecan4 or Pax7, both of which are important for satellite cell function and development. Moreover, we show that muscle hypertrophy after pharmacological blockade of this pathway occurs without significant satellite cell proliferation and fusion to myofibers and without an increase in the number of myonuclei per myofiber. Finally, we show that genetic ablation of Acvr2b, which encodes a high-affinity receptor for myostatin and activin A specifically in myofibers is sufficient to induce muscle hypertrophy. All of these findings are consistent with satellite cells playing little or no role in myostatin/activin A signaling in vivo and render support that inhibition of this signaling pathway can be an effective therapeutic approach for increasing muscle growth even in disease settings characterized by satellite cell dysfunction.
Asunto(s)
Activinas/metabolismo , Fibras Musculares Esqueléticas/citología , Miostatina/metabolismo , Células Satélite del Músculo Esquelético/citología , Transducción de Señal/fisiología , Receptores de Activinas Tipo II/genética , Receptores de Activinas Tipo II/metabolismo , Animales , Folistatina/genética , Folistatina/metabolismo , Hipertrofia , Fusión de Membrana/fisiología , Ratones , Ratones de la Cepa 129 , Ratones Endogámicos C57BL , Ratones Transgénicos , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/citología , Músculo Esquelético/fisiología , Tamaño de los Órganos , Factor de Transcripción PAX7/genética , Factor de Transcripción PAX7/metabolismo , Regeneración/fisiología , Células Satélite del Músculo Esquelético/metabolismo , Sindecano-4/genética , Sindecano-4/metabolismoRESUMEN
We report the generation of five mouse strains with the tamoxifen-inducible Cre (Cre-ER(T) (2) ; CE) gene cassette knocked into the endogenous loci of Pax3, Myod1, Myog, Myf6, and Myl1, collectively as a resource for the skeletal muscle research community. We characterized these CE strains using the Cre reporter mice, R26R(L) (acZ) , during embryogenesis and show that they direct tightly controlled tamoxifen-inducible reporter expression within the expected cell lineage determined by each myogenic gene. We also examined a few selected adult skeletal muscle groups for tamoxifen-inducible reporter expression. None of these new CE alleles direct reporter expression in the cardiac muscle. All these alleles follow the same knock-in strategy by replacing the first exon of each gene with the CE cassette, rendering them null alleles of the endogenous gene. Advantages and disadvantages of this design are discussed. Although we describe potential immediate use of these strains, their utility likely extends beyond foreseeable questions in skeletal muscle biology.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Desarrollo de Músculos/genética , Músculo Esquelético/citología , Moduladores Selectivos de los Receptores de Estrógeno/farmacología , Tamoxifeno/farmacología , Alelos , Animales , Linaje de la Célula , Técnicas de Sustitución del Gen , Ratones , Músculo Esquelético/crecimiento & desarrolloRESUMEN
Skeletal muscle tissue provides mechanical force for locomotion of all vertebrate animals. It is prone to damage from acute physical trauma and physiological stress. To cope with this, it possesses a tremendous capacity for rapid and effective repair that is widely held to be accomplished by the satellite cells lying between the muscle fiber plasmalemma and the basement membrane. Cell transplantation and lineage-tracing studies have demonstrated that Pax7-expressing (Pax7(+)) satellite cells can repair damaged muscle tissue repeatedly after several bouts of acute injury. These findings provided evidence that Pax7(+) cells are muscle stem cells. However, stem cells from a variety of other origins are also reported to contribute to myofibers upon engraftment into muscles, questioning whether satellite cells are the only stem cell source for muscle regeneration. Here, we have engineered genetic ablation of Pax7(+) cells to test whether there is any significant contribution to muscle regeneration after acute injury from cells other than this source. We find that such elimination of Pax7(+) cells completely blocks regenerative myogenesis either following injury to the tibialis anterior (TA) muscle or after transplantation of extensor digitorum longus (EDL) muscles into nude mice. As Pax7 is specifically expressed in satellite cells, we conclude that they are essential for acute injury-induced muscle regeneration. It remains to be established whether there is any significant role for stem cells of other origins. The implications of our results for muscle stem cell-based therapy are discussed.
Asunto(s)
Músculo Esquelético/citología , Músculo Esquelético/fisiología , Factor de Transcripción PAX7/metabolismo , Células Satélite del Músculo Esquelético/citología , Células Satélite del Músculo Esquelético/metabolismo , Animales , Bungarotoxinas/farmacología , Cardiotoxinas/farmacología , Proliferación Celular/efectos de los fármacos , Toxina Diftérica/farmacología , Femenino , Técnica del Anticuerpo Fluorescente , Masculino , Ratones , Ratones Mutantes , Ratones Desnudos , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/metabolismo , Factor de Transcripción PAX7/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Células Satélite del Músculo Esquelético/fisiología , Tamoxifeno/farmacologíaRESUMEN
Genesis of skeletal muscle relies on the differentiation and fusion of mono-nucleated muscle progenitor cells into the multi-nucleated muscle fiber syncytium. The temporally-controlled cellular and morphogenetic changes underlying this process are initiated by a series of highly coordinated transcription programs. At the core, the myogenic differentiation cascade is driven by muscle-specific transcription factors, i.e., the Myogenic Regulatory Factors (MRFs). Despite extensive knowledge on the function of individual MRFs, very little is known about how they are coordinated. Ultimately, highly specific coordination of these transcription programs is critical for their masterfully timed transitions, which in turn facilitates the intricate generation of skeletal muscle fibers from a naïve pool of progenitor cells. The Mediator complex links basal transcriptional machinery and transcription factors to regulate transcription and could be the integral component that coordinates transcription factor function during muscle differentiation, growth, and maturation. In this study, we systematically deciphered the changes in Mediator complex subunit expression in skeletal muscle development, regeneration, aging, and disease. We incorporated our in vitro and in vivo experimental results with analysis of publicly available RNA-seq and single nuclei RNA-seq datasets and uncovered the regulation of Mediator subunits in different physiological and temporal contexts. Our experimental results revealed that Mediator subunit expression during myogenesis is highly dynamic. We also discovered unique temporal patterns of Mediator expression in muscle stem cells after injury and during the early regeneration period, suggesting that Mediator subunits may have unique contributions to directing muscle stem cell fate. Although we observed few changes in Mediator subunit expression in aging muscles compared to younger muscles, we uncovered extensive heterogeneity of Mediator subunit expression in dystrophic muscle nuclei, characteristic of chronic muscle degeneration and regeneration cycles. Taken together, our study provides a glimpse of the complex regulation of Mediator subunit expression in the skeletal muscle cell lineage and serves as a springboard for mechanistic studies into the function of individual Mediator subunits in skeletal muscle.
RESUMEN
The regulation of proteostasis is fundamental for maintenance of muscle mass and function. Activation of the TGF-ß pathway drives wasting and premature aging by favoring the proteasomal degradation of structural muscle proteins. Yet, how this critical post-translational mechanism is kept in check to preserve muscle health remains unclear. Here, we reveal the molecular link between the post-transcriptional regulation of m6A-modified mRNA and the modulation of SMAD-dependent TGF-ß signaling. We show that the m6A-binding protein YTHDF2 is essential to determining postnatal muscle size. Indeed, muscle-specific genetic deletion of YTHDF2 impairs skeletal muscle growth and abrogates the response to hypertrophic stimuli. We report that YTHDF2 controls the mRNA stability of the ubiquitin ligase ASB2 with consequences on anti-growth gene program activation through SMAD3. Our study identifies a post-transcriptional to post-translational mechanism for the coordination of gene expression in muscle.
Asunto(s)
Proteostasis , Factores de Transcripción , Factores de Transcripción/metabolismo , Regulación de la Expresión Génica , Factor de Crecimiento Transformador beta/metabolismo , Músculos/metabolismo , Proteína smad3/genética , Proteína smad3/metabolismoRESUMEN
Adult stem cells play a critical role in tissue repair and maintenance. In tissues with slow turnover, including skeletal muscle, these cells are maintained in a mitotically quiescent state yet remain poised to re-enter the cell cycle to replenish themselves and regenerate the tissue. Using a panomics approach we show that the PAX7/NEDD4L axis acts against muscle stem cell activation in homeostatic skeletal muscle. Our findings suggest that PAX7 transcriptionally activates the E3 ubiquitin ligase Nedd4L and that the conditional genetic deletion of Nedd4L impairs muscle stem cell quiescence, with an upregulation of cell cycle and myogenic differentiation genes. Loss of Nedd4L in muscle stem cells results in the expression of doublecortin (DCX), which is exclusively expressed during their in vivo activation. Together, these data establish that the ubiquitin proteasome system, mediated by Nedd4L, is a key contributor to the muscle stem cell quiescent state in adult mice.
RESUMEN
Somatic stem cells are tissue-specific reserve cells tasked to sustain tissue homeostasis in adulthood and/or effect tissue regeneration after traumatic injury. The stem cells of skeletal muscle tissue are the satellite cells, which were originally described and named after their localization beneath the muscle fiber lamina and attached to the multi-nucleated muscle fibers. During adult homeostasis, satellite cells are maintained in quiescence, a state of reversible cell cycle arrest. Yet, upon injury, satellite cells are rapidly activated, becoming highly mitotically active to generate large numbers of myoblasts that differentiate and fuse to regenerate the injured muscle fibers. A subset self-renews to replenish the pool of muscle stem cells.Complex intrinsic gene regulatory networks maintain the quiescent state of satellite cells, or upon injury, direct their activation, proliferation, differentiation and self-renewal. Molecular cues from the satellite cells' environment provide the essential information as to when and where satellite cells are to stay quiescent or break quiescence and effect regenerative myogenesis. Predominantly, these cues are secreted, diffusible or membrane-bound ligands that bind to and activate their specific cognate receptors on the satellite cell to activate downstream signaling cascades and elicit context-specific cell behavior. This review aims to offer a concise overview of major intercellular signaling pathways regulating satellite cells during quiescence and in injury-induced skeletal muscle regeneration.
Asunto(s)
Músculo Esquelético , Células Satélite del Músculo Esquelético , Músculo Esquelético/fisiología , Fibras Musculares Esqueléticas/metabolismo , Diferenciación Celular/genética , Transducción de Señal , Células MadreRESUMEN
Multinucleated skeletal muscle cells have an obligatory need to acquire additional nuclei through fusion with activated skeletal muscle stem cells when responding to both developmental and adaptive growth stimuli. A fundamental question in skeletal muscle biology has been the reason underlying this need for new nuclei in syncytial cells that already harbor hundreds of nuclei. To begin to answer this long-standing question, we utilized nuclear RNA-sequencing approaches and developed a lineage tracing strategy capable of defining the transcriptional state of recently fused nuclei and distinguishing this state from that of pre-existing nuclei. Our findings reveal the presence of conserved markers of newly fused nuclei both during development and after a hypertrophic stimulus in the adult. However, newly fused nuclei also exhibit divergent gene expression that is determined by the myogenic environment to which they fuse. Moreover, accrual of new nuclei through fusion is required for nuclei already resident in adult myofibers to mount a normal transcriptional response to a load-inducing stimulus. We propose a model of mutual regulation in the control of skeletal muscle development and adaptations, where newly fused and pre-existing myonuclear populations influence each other to maintain optimal functional growth.
RESUMEN
Apelin (Apln) is a myokine that regulates skeletal muscle plasticity and metabolism and declines during aging. Through a yeast one-hybrid transcription factor binding screen, we identified the TEA domain transcription factor 1 (Tead1) as a novel regulator of the Apln promoter. Single-cell analysis of regenerating muscle revealed that the apelin receptor (Aplnr) is enriched in endothelial cells, whereas Tead1 is enriched in myogenic cells. Knock-down of Tead1 stimulates Apln secretion from muscle cells in vitro and myofiber-specific overexpression of Tead1 suppresses Apln secretion in vivo. Apln secretion via Tead1 knock-down in muscle cells stimulates endothelial cell expansion via endothelial Aplnr. In vivo, Apln peptide supplementation enhances endothelial cell expansion while Tead1 muscle overexpression delays endothelial remodeling following muscle injury. Our work describes a novel paracrine crosstalk in which Apln secretion is controlled by Tead1 in myogenic cells and influences endothelial remodeling during muscle repair.
RESUMEN
Skeletal muscle stem cells, i.e., satellite cells (SCs), are the essential source of new myonuclei for skeletal muscle regeneration following injury or chronic degenerative myopathies. Both SC number and regenerative capacity diminish during aging. However, molecular regulators that govern sizing of the initial SC pool are unknown. We demonstrate that fibroblast growth factor 6 (FGF6) is critical for SC pool scaling. Mice lacking FGF6 have reduced SCs of early postnatal origin and impaired regeneration. By contrast, increasing FGF6 during the early postnatal period is sufficient for SC expansion. Together, these data support that FGF6 is necessary and sufficient to modulate SC numbers during a critical postnatal period to establish the quiescent adult muscle stem cell pool. Our work highlights postnatal development as a time window receptive for scaling a somatic stem cell population via growth factor signaling, which might be relevant for designing new biomedical strategies to enhance tissue regeneration.
Asunto(s)
Factor 6 de Crecimiento de Fibroblastos/metabolismo , Músculo Esquelético/patología , Células Madre/patología , Animales , Animales Recién Nacidos , Proliferación Celular , Ratones Endogámicos C57BL , Ratones Mutantes , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/lesiones , RegeneraciónRESUMEN
We have generated a mouse strain carrying a Cre-ER(T2) knock-in allele at the Pax7 locus, the Pax7(CE) allele (Lepper et al., 2009, Nature 460:627-631). Combining Pax7(CE) and the R26R(LacZ) Cre reporter allele, here we describe temporal-specific tamoxifen (tmx)-inducible lineage tracing of embryonic Pax7-expressing cells. In particular, we focus on the somitic lineage. Tmx-inducible Cre activity directed by the Pax7(CE) allele is similar to the endogenous Pax7 expression pattern. The somitic Pax7-expressing cells selectively marked at embryonic day 9.5 (E9.5) give rise to dorsal dermis and brown adipose tissue, in addition to dorsal aspects of trunk muscles and the diaphragm muscle. However, they do not contribute to ventral body wall and limb muscles. After E12.5, marked Pax7-expressing cells become lineage restricted to muscles. Descendants of these early marked Pax7-expressing cells begin to occupy sublaminal positions associated with the myofibers around E16.5, characteristic of embryonic satellite cells. Furthermore, they contribute to adult myofibers and regeneration competent satellite cells in the tibialis anterior muscle, providing evidence that some adult satellite cells are of embryonic origin.
Asunto(s)
Diferenciación Celular , Linaje de la Célula/fisiología , Fibras Musculares Esqueléticas/fisiología , Factor de Transcripción PAX7/genética , Regeneración/fisiología , Células Satélite del Músculo Esquelético/fisiología , Células Madre/fisiología , Factores de Edad , Animales , Embrión de Mamíferos/citología , Regulación del Desarrollo de la Expresión Génica , Inmunohistoquímica , Ratones , Ratones Transgénicos , Modelos Biológicos , Desarrollo de Músculos/fisiología , Fibras Musculares Esqueléticas/citología , Regeneración/genética , Células Satélite del Músculo Esquelético/citología , Somitos/citología , Células Madre/citología , TamoxifenoRESUMEN
Muscle undergoes progressive weakening and regenerative dysfunction with age due in part to the functional decline of skeletal muscle stem cells (MuSCs). MuSCs are heterogeneous but whether their gene expression changes with age and the implication of such changes are unclear. Here we show that in mice, Growth arrest-specific gene 1 (Gas1) is expressed in a small subset of young MuSCs with its expression progressively increasing in larger fractions of MuSCs later in life. Over-expression of Gas1 in young MuSCs and inactivation of Gas1 in aged MuSCs support that Gas1 reduces the quiescence and self-renewal capacity of MuSCs. Gas1 reduces Ret signaling, which is required for MuSC quiescence and self-renewal. Indeed, we show that the Ret ligand, Glial Cell-Derived Neurotrophic Factor (GDNF), can counteract Gas1 by stimulating Ret signaling and enhancing MuSC self-renewal and regeneration, thus improving muscle function. We propose that strategies aimed to target this pathway can be exploited to improve the regenerative decline of muscle stem cells.
Asunto(s)
Proteínas de Ciclo Celular/genética , Autorrenovación de las Células/genética , Factor Neurotrófico Derivado de la Línea Celular Glial/genética , Músculo Esquelético/citología , Células Madre/metabolismo , Envejecimiento/efectos de los fármacos , Animales , División Celular , Femenino , Proteínas Ligadas a GPI/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Músculo Esquelético/crecimiento & desarrollo , Proteínas Proto-Oncogénicas c-ret/fisiología , Regeneración/genética , Regeneración/fisiología , Transducción de Señal , TranscriptomaRESUMEN
Satellite cells are muscle stem cells required for muscle regeneration upon damage. Of note, satellite cells are bipotent and have the capacity to differentiate not only into skeletal myocytes, but also into brown adipocytes. Epigenetic mechanisms regulating fate decision and differentiation of satellite cells during muscle regeneration are not yet fully understood. Here, we show that elevated levels of lysine-specific demethylase 1 (Kdm1a, also known as Lsd1) have a beneficial effect on muscle regeneration and recovery after injury, since Lsd1 directly regulates key myogenic transcription factor genes. Importantly, selective Lsd1 ablation or inhibition in Pax7-positive satellite cells, not only delays muscle regeneration, but changes cell fate towards brown adipocytes. Lsd1 prevents brown adipocyte differentiation of satellite cells by repressing expression of the novel pro-adipogenic transcription factor Glis1. Together, downregulation of Glis1 and upregulation of the muscle-specific transcription program ensure physiological muscle regeneration.
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Adipocitos Marrones/metabolismo , Proteínas de Unión al ADN/genética , Histona Demetilasas/genética , Fibras Musculares Esqueléticas/metabolismo , Regeneración/genética , Células Satélite del Músculo Esquelético/metabolismo , Factores de Transcripción/genética , Adipocitos Marrones/citología , Animales , Diferenciación Celular , Línea Celular , Proliferación Celular , Proteínas de Unión al ADN/metabolismo , Epigénesis Genética , Histona Demetilasas/metabolismo , Ratones , Ratones Endogámicos C57BL , Desarrollo de Músculos/genética , Fibras Musculares Esqueléticas/citología , Músculo Esquelético/lesiones , Músculo Esquelético/metabolismo , Factor de Transcripción PAX7/genética , Factor de Transcripción PAX7/metabolismo , Cultivo Primario de Células , Células Satélite del Músculo Esquelético/citología , Transducción de Señal , Factores de Transcripción/metabolismoRESUMEN
When unperturbed, somatic stem cells are poised to affect immediate tissue restoration upon trauma. Yet, little is known regarding the mechanistic basis controlling initial and homeostatic 'scaling' of stem cell pool sizes relative to their target tissues for effective regeneration. Here, we show that TEAD1-expressing skeletal muscle of transgenic mice features a dramatic hyperplasia of muscle stem cells (i.e. satellite cells, SCs) but surprisingly without affecting muscle tissue size. Super-numeral SCs attain a 'normal' quiescent state, accelerate regeneration, and maintain regenerative capacity over several injury-induced regeneration bouts. In dystrophic muscle, the TEAD1 transgene also ameliorated the pathology. We further demonstrate that hyperplastic SCs accumulate non-cell-autonomously via signal(s) from the TEAD1-expressing myofiber, suggesting that myofiber-specific TEAD1 overexpression activates a physiological signaling pathway(s) that determines initial and homeostatic SC pool size. We propose that TEAD1 and its downstream effectors are medically relevant targets for enhancing muscle regeneration and ameliorating muscle pathology.
Asunto(s)
Proliferación Celular , Proteínas de Unión al ADN/genética , Distrofina/deficiencia , Expresión Génica , Proteínas Nucleares/genética , Células Satélite del Músculo Esquelético/fisiología , Factores de Transcripción/genética , Animales , Ratones Endogámicos C57BL , Ratones Transgénicos , Factores de Transcripción de Dominio TEARESUMEN
Skeletal muscle regeneration relies on a pool of resident muscle stem cells called satellite cells (MuSCs). Following injury-induced destruction of the myofibers, quiescent MuSCs are activated and generate transient amplifying progenitors (myoblasts) that will fuse to form new myofibers. Here, we focus on the canonical Wnt signaling pathway and find that either conditional ß-catenin disruption or activation in adult MuSCs results in perturbation of muscle regeneration. Using both in vivo and in vitro approaches, we observed that myoblasts lacking ß-catenin show delayed differentiation, whereas myoblasts with constitutively active ß-catenin undergo precocious growth arrest and differentiation. Transcriptome analysis further demonstrated that Wnt/ß-catenin signaling interacts with multiple pathways and, more specifically, TGF-ß signaling. Indeed, exogenous TGF-ß2 stimulation restores the regenerative potential of muscles with targeted ß-catenin disruption in MuSCs. We conclude that a precise level of ß-catenin activity is essential for regulating the amplification and differentiation of MuSC descendants during adult myogenesis.
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Músculos/citología , Células Madre/citología , Cicatrización de Heridas , beta Catenina/metabolismo , Animales , Diferenciación Celular , Proliferación Celular , Eliminación de Gen , Marcación de Gen , Ratones Noqueados , Desarrollo de Músculos , Mioblastos/citología , Regeneración , Transducción de Señal , Células Madre/metabolismo , Factor de Crecimiento Transformador beta/metabolismoRESUMEN
Skeletal muscle contains Pax7-expressing muscle stem or satellite cells, enabling muscle regeneration throughout most of adult life. Here, we demonstrate that induced inactivation of Pax7 in Pax7-expressing cells of adult mice leads to loss of muscle stem cells and reduced heterochromatin condensation in rare surviving satellite cells. Inactivation of Pax7 in Myf5-expressing cells revealed that the majority of adult muscle stem cells originate from myogenic lineages, which express the myogenic regulators Myf5 or MyoD. Likewise, the majority of muscle stem cells are replenished from Myf5-expressing myogenic cells during adult life, and inactivation of Pax7 in Myf5-expressing cells after muscle damage leads to a complete arrest of muscle regeneration. Finally, we demonstrate that a relatively small number of muscle stem cells are sufficient for efficient repair of skeletal muscles. We conclude that Pax7 acts at different levels in a nonhierarchical regulatory network controlling muscle-satellite-cell-mediated muscle regeneration.
Asunto(s)
Células Madre Adultas/citología , Células Madre Adultas/metabolismo , Factor 5 Regulador Miogénico/metabolismo , Factor de Transcripción PAX7/metabolismo , Células Satélite del Músculo Esquelético/metabolismo , Animales , Ratones , Factor 5 Regulador Miogénico/genética , Factor de Transcripción PAX7/genética , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, whereas undifferentiated pleomorphic sarcoma (UPS) is one of the most common soft tissue sarcomas diagnosed in adults. To investigate the myogenic cell(s) of origin of these sarcomas, we used Pax7-CreER and MyoD-CreER mice to transform Pax7(+) and MyoD(+) myogenic progenitors by expressing oncogenic Kras(G12D) and deleting Trp53 in vivo. Pax7-CreER mice developed RMS and UPS, whereas MyoD-CreER mice developed UPS. Using gene set enrichment analysis, RMS and UPS each clustered specifically within their human counterparts. These results suggest that RMS and UPS have distinct and overlapping cells of origin within the muscle lineage. Taking them together, we have established mouse models of soft tissue sarcoma from muscle stem and progenitor cells.