Bioscience Methods 2025, Vol.16, No.2, 83-99 http://bioscipublisher.com/index.php/bm 85 Myf6 are expressed at high levels, which helps promote their differentiation into myoblasts. After birth, the growth of muscle fibers is mainly achieved through the proliferation and differentiation of satellite cells. Satellite cells are adult stem cells located under the basement membrane of muscle fibers. They are usually in a quiescent state. Once they are damaged or stimulated by growth, they are activated to proliferate, and some new cells fuse into muscle fibers, thereby providing new nuclei to support muscle fiber hypertrophy. It should be noted that without satellite cells to supply new nuclei, the continuous hypertrophy of muscle fibers will be limited. Therefore, satellite cells play a key role in postnatal muscle growth and regeneration and repair. Throughout the process of muscle development, vascularization and innervation of muscle tissue also proceed synchronously to ensure that muscle fibers receive sufficient nutrition and signals. These steps together constitute the key stage of skeletal muscle development in goats and even mammals. 2.2 Cellular and molecular participants The development of goat skeletal muscle involves the cooperation of multiple cell types and molecular participants. Muscle lineage cells include myogenic precursors, myoblasts and muscle fibers, as well as satellite cells that play an important role in the adult stage. In addition, there are non-myogenic stromal cells involved in regulating the microenvironment of muscle development, such as fibroblasts, adipocytes, and vascular endothelial cells. Among them, fibroblast/adipogenic progenitors (FAPs) are a type of mesenchymal stromal cells that have the potential to differentiate into fibroblasts or adipocytes and play a role in muscle damage repair and fat deposition. The latest study by Zhu et al. (2024) showed that there are multiple FAP subpopulations in goat skeletal muscle, and their differentiation trajectory is related to intramuscular fat (adipogenesis). Different cells in muscle tissue communicate through paracrine signals. For example, FAPs interact with satellite cells through growth differentiation factor (GDF), insulin-like growth factor (IGF) and other signals to affect muscle fiber formation and fat deposition. At the molecular level, growth factors and cytokines constitute an important part of the muscle development regulatory network. For example, IGF-1 can promote myoblast differentiation and muscle fiber hypertrophy, while the TGF-β/Myostatin pathway inhibits myocyte proliferation and differentiation, thereby limiting muscle growth. Factors that regulate the conversion of muscle fiber types include calcium signaling pathways. The calcium-dependent protein phosphatase calcineurin can activate transcription factors such as NFATc1, which tends to favor the expression of slow muscle fiber genes. In contrast, the pathway activated by FoxO1 is conducive to the formation of fast muscle fiber characteristics (Figure 1) (Cao et al., 2023). Figure 1 Summary of potential regulatory patterns of DNA 5mC and accessible chromatin regions on gene expression (Adopted from Cao et al., 2023)
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