Molecular profiling of satellite cell heterogeneity during differentiation in an individual turkey pectoralis major muscle.

Satellite cells are muscle stem cells that contribute to post-hatch muscle growth by fusing with adjacent muscle fibers, thereby promoting muscle fiber hypertrophy. Satellite cells are not a uniform population; even within a single muscle, such as the turkey pectoralis major, they exhibit substantial variability in their proliferative capacity. To better understand this cellular heterogeneity, we performed transcriptomic profiling of individual satellite cell clones isolated from the same turkey pectoralis major muscle after 48 hours of differentiation. These clones had been previously categorized as early (fast-growing) or late (slow-growing) based on their proliferation rates. Principal Component Analysis revealed a clear separation in transcriptomic profiles between early and late clones, with over 1,400 genes differentially expressed. Gene ontology analysis indicated that early clones were enriched for genes involved in organ development and receptor signaling, while late clones upregulated genes associated with cell proliferation and peptidase activator activity. Notably, among the top 10 most significantly differentially expressed genes, MSTN was highly upregulated in early clones, while FGFBP1 showed elevated expression in late clones. MSTN is a well-established negative regulator of satellite cell proliferation and differentiation, whereas FGFBP1 modulates FGF signaling, thereby promoting both proliferation and differentiation. Both genes play critical roles in regulating satellite cell differentiation, and their differential expression patterns have important implications for breast muscle growth. Despite these differences, expression levels of PAX7 and other key myogenic regulatory factors remained comparable between the two groups, suggesting that their core myogenic identity was preserved. Collectively, these findings underscore the intrinsic genetic heterogeneity of satellite cell populations within a single muscle during differentiation. Together with our previous results showing marked transcriptional differences after 72 hours of proliferation, these data provide consistent evidence that turkey satellite cells maintain distinct molecular identities across both proliferative and differentiative stages.