Characterization of Fiber-Type Composition and Phosphoproteins of Fast- and Slow-Growing Broilers

Muscle fibers exhibit high plasticity: both the fast-twitch fiber type and slow-twitch fiber type can mutually transform under the regulation of phosphorylation. In this study, we characterized the muscle fiber profiles and phosphoproteomes of the m. extensor digitorum longus (EDL) and m. soleus (SOL) in slow-growing Xueshan chickens and fast-growing Ross 308 broilers. Fiber-type distribution was quantified by immunohistochemistry and RT-qPCR of MYH7B, MYH1A and MYH1B. TMT-based phosphoproteomics, combined with bioinformatic analysis, was used to identify differentially expressed phosphopeptides (DEPs) in two comparisons: Ross 308 SOL vs. Ross 308 EDL, and Xueshan EDL vs. Ross 308 EDL. The proportion of type I (slow-twitch) fibers in EDL was significantly higher in Xueshan chickens than in Ross 308 broilers (15.53% vs. 6.14%, p < 0.05), with no significant differences in fiber distribution or diameter between the SOL and EDL in Xueshan chickens (p > 0.05). A total of 3226 phosphopeptides corresponding to 1762 phosphoproteins were identified, with serine as the most abundant phosphorylated amino acid (73.92%). PDHA1, PHKB and PGAM1 were identified as the key DEPs common to both comparison groups. Bioinformatic analyses revealed that reversible site-specific phosphorylation regulates avian muscle fiber-type transformation mainly via the glycolysis/gluconeogenesis pathway.