Jul 2026· Current Opinion in Genetics and Development· Vol 100, pp.
102516
· 1 citation· 77 references
Medicine
TL;DR
Emerging principles of myonuclear plasticity and spatial specialization are discussed, which reveal how myogenic nuclei undergo dynamic state transitions in response to interactions with surrounding cell types, and how these states can be remodeled during regeneration.
Abstract
Skeletal muscle exhibits an unusually complex architecture, in which large multinucleated myofibers accommodate a small population of resident muscle stem cells (MuSCs) along their surface. In addition, myofibers contain molecularly and functionally specialized domains at junctions with motor neurons and tendons. Regeneration of this tissue, therefore, requires a coordinated series of events, spanning MuSC activation, proliferation, fusion to restore myofiber mass, as well as reconstruction of specialized domains. Recent advances have begun to reveal how myogenic nuclei undergo dynamic state transitions in response to interactions with surrounding cell types, and how these states can be remodeled during regeneration. Here, we discuss emerging principles of myonuclear plasticity and spatial specialization.
Precise neuromuscular connectivity depends on coordinated interactions between motor axons and their muscle targets during development. In the Drosophila embryo, dynamic muscle protrusions termed myopodia arise during early phases of muscle innervation and have been proposed to contribute to synaptic partner matching. However, whether similar structures occur across different muscle fibers and how they are developmentally regulated remain unclear. Here, we developed a genetic imaging toolkit based on GAL4 drivers that label defined subsets of embryonic muscle fibers or enable stochastic single-muscle visualization across the musculature. These reagents allow minimally invasive, high-resolution imaging of muscle membrane dynamics in both live and fixed embryos. Using this approach, we found that myopodial clustering is not restricted to a single muscle but is observed across multiple muscle fibers at presumptive synaptic contact sites. Importantly, clustered myopodia emerged during a defined developmental window coincident with motor axon arrival at target muscles, indicating that clustering is temporally associated with neuron-muscle interactions. While clustering was observed in multiple muscles, its frequency and morphology exhibited quantitative variation among muscle fibers. Together, these findings establish myopodial clustering as a recurrent and temporally regulated cellular behavior in the presumptive postsynaptic sites of ventral muscles during early neuromuscular contact development. This study provides a versatile toolkit and a framework for systematically analyzing muscle membrane dynamics during synaptic target recognition.
Melissa Ana Inal, Daichi Kamiyama· Developmental Biology· 0 citations
Stem cell–mediated regeneration is essential for tissue integrity. In skeletal muscle, tissue repair largely depends on muscle stem cells (MuSCs), which undergo dynamic cell-state transitions through making precise fate decisions during regeneration. However, the molecular regulators of cell-state conversion in MuSCs remain unclear. Here, we identify a previously unrecognized, noncanonical role for TRF2 in MuSC biology. TRF2 is dynamically regulated upon injury and required to preserve stem cell identity, support reparative myogenesis, and sustain self-renewal. MuSC-specific TRF2 disruption exacerbates muscular dystrophy pathology in mice, recapitulating key features of human disease. Mechanistically, TRF2 associates with regulatory regions enriched for DNA G-quadruplex–forming sequences at lineage-specific genes, sustaining their expression. These findings establish TRF2 as a pivotal regulator of adult stem cell function and tissue-specific regenerative responses.
Ji-Hyung Lee, Kiran Nakka, Ryan P. Calhoun et al.· Science Advances· 0 citations
Skeletal muscle possesses a remarkable capacity for regeneration, a process tightly regulated by interactions between resident stem cells and the immune system. Following injury, a complex cascade of events is initiated, involving the infiltration of immune cells that clear debris and create a pro-regenerative environment. Among these, macrophages are critical mediators, exhibiting significant plasticity that allows them to switch from a pro-inflammatory to a pro-reparative phenotype. However, the full spectrum of macrophage heterogeneity and their precise communication with muscle cells remains elusive.
Here, we present the first single-nucleus RNA sequencing (snRNA-seq) analysis of regenerating skeletal muscle, providing an unprecedented high-resolution view of the nuclear transcriptional landscape during tissue repair. This approach overcomes the limitations of single-cell RNA sequencing (scRNA-seq) by capturing transcripts from multinucleated myofibers and minimizing cellular stress artifacts.
Our analysis identified three distinct macrophage subpopulations with unique transcriptional and spatial profiles. We uncovered a differential regulation axis linked to CSF-1 and IL-34, where IL-34 is expressed by smooth muscle cells in proximity to resting macrophages in the perimysium and epimysium, while CSF-1 expression is transiently upregulated by fibroblasts during inflammation. Comparative analysis of aged and dystrophic (mdx and BLA/J) mouse models demonstrated a direct correlation between the degree of inflammation, the abundance of macrophage and fibroblast populations, and the expression levels of CSF-1 and IL-34.
These findings provide novel insights into macrophage heterogeneity in muscle physiology and pathology, suggesting that selectively targeting CSF-1 is a superior strategy for depleting pro-inflammatory macrophages in muscular dystrophies and age-related muscle decline.
2021R1I1A3059820 (National Research Foundation of Korea)
Computational and Systems Immunology (COMP)
Jea-Hyun Baek, W. Byun, Eun-Chong Bang et al.· Journal of Immunology· 0 citations
Adult zebrafish efficiently regenerate skeletal muscle following different types of injury; however, the molecular programs involved in repair after extensive cryoinjury remain to be comprehensively characterized. Here, we explored the transcriptomic response of adult zebrafish skeletal muscle at 7 days post cryoinjury (dpci), a stage marked by ongoing tissue clearance, progenitor expansion, myogenic differentiation, and nascent myofiber formation, and compared it with phase-matched stab wound injury. Cryoinjury induced a broad transcriptional response, with 5,330 differentially expressed genes. Integrated enrichment and protein–protein interaction analyses revealed that, at 7 dpci, zebrafish skeletal muscle functions as an integrated regenerative system in which immune remodeling, progenitor expansion, myogenic differentiation, extracellular matrix reconstruction, mechanotransduction, biosynthetic adaptation, proteostasis, and intracellular trafficking operate simultaneously. In parallel, mature sarcomeric and oxidative metabolic programs were suppressed, consistent with ongoing tissue reconstruction and structural immaturity. Comparison with stab-wounded skeletal muscle revealed substantial transcriptional conservation, as 612 of 717 stab-wound-responsive genes (85%) were also differentially expressed after cryoinjury. Shared upregulated genes formed coherent functional modules related to proliferation, extracellular matrix organization and signaling, immune regulation, muscle differentiation, and protein processing. Thus, distinct injury modalities converge on a common regenerative program, while cryoinjury elicits a quantitatively broader transcriptional response. These findings support a conserved regenerative architecture of adult zebrafish skeletal muscle repair, in which interconnected biological modules act coordinately, with the breadth of transcriptional engagement reflecting regenerative demand.
Abstract Skeletal muscle regeneration depends on the coordinated activity of multiple cell populations within the muscle stem cell niche, most prominently macrophages, which undergo dynamic phenotypic transitions essential to tissue repair. Aging disrupts this process, impairing macrophage signaling and muscle stem cell function in ways that are not yet fully understood. Existing approaches (e.g. conditioned media transfer and indirect transwell co-culture) fail to recapitulate the direct cell-to-cell contact required for continuous, reciprocal regulation throughout the regenerative cascade. Here, we present a protocol for the isolation of bone marrow-derived and tissue-resident macrophages from skeletal muscle, together with a direct co-culture methodology designed to interrogate macrophage–myoblast interactions in an age-relevant context.
Ryan Arsenault, Anthony Ziadeh, Alex E. Green et al.· Biology Methods and Protocol...· 0 citations
