The role of -regulatory elements in the determination and transformation of muscle fiber type in animal skeletal muscles.

Muscle fibers are the fundamental units of skeletal muscle. Based on contraction speed and metabolic properties, muscle fibers are categorized into fast-twitch and slow-twitch fibers. Further subdivision based on MyHC gene isoforms identifies them as type I, IIA, IIB, and IIX fibers. There is potential for interconversion among these muscle fiber types. The proportions of different muscle fibers determine muscle functional properties and affect muscle quality. Compared with muscles mainly harboring fast-twitch fibers, muscles predominantly composed of slow-twitch fibers are characterized by enhanced water-holding capacity, tenderness, and superior flavor. During the formation and transformation of animal skeletal muscle fibers, the expression of a series of muscle-specific genes is precisely regulated by -regulatory elements. These -regulatory elements achieve precise regulation of the target genes through interactions with transcription factors and other regulatory proteins, thereby ensuring the formation and transformation of muscle fibers. Based on introducing the types and characteristics of muscle fibers, we summarize and prospect the role of the transcription factors and -regulatory elements in the formation and transformation of fast-twitch and slow-twitch muscle fibers in livestock. The aim of this review is to deepen the understanding of the relationship between gene expression regulation and muscle fiber diversity, and to provide theoretical support for the improvement of meat quality in livestock.