Comparative phosphoproteomic analysis reveals regulatory mechanisms underlying muscle fiber density in goslings

Muscle fiber density at hatching is closely associated with post-hatch meat yield through subsequent hypertrophy and with meat tenderness at market age. However, inter-individual variation in muscle fiber traits among goslings remains poorly understood. In this study, 129 one-day-old Yangzhou goslings were sampled and classified into three phenotypic groups based on gastrocnemius muscle weight and muscle fiber density: high meat yield-high fiber density (HH; 0.56 ± 0.01 g, 7803.88 ± 434.12 n/mm²), high meat yield-low fiber density (HL; 0.59 ± 0.03 g, 3847.01 ± 135.68 n/mm²), and low meat yield (LY; 0.46 ± 0.02 g, characterized by lower body weight and muscle mass). A 4D label-free quantitative phosphoproteomic approach was then applied to uncover phosphorylation-mediated mechanisms regulating early muscle fiber development. In total, 6,412 phosphorylation sites corresponding to 5,548 phosphopeptides and 2,519 phosphoproteins were quantified. Compared with HL goslings, HH goslings exhibited elevated phosphorylation of muscle structural proteins (e.g., MYOM2 Thr614, Lamin A/C Ser299), cytoskeletal proteins (e.g., PDLIM7 Ser126, FLN Ser1524), and MAPK signaling components (p38-MAPK Thr180), correlating with higher fiber density. Conversely, HL goslings showed increased phosphorylation of kinases and energy metabolism proteins (e.g., CaMK Thr288, PGM1 Thr507/Ser408), consistent with enhanced fiber hypertrophy. KEGG enrichment indicated involvement of actin cytoskeleton regulation, MAPK signaling, and glycolysis/gluconeogenesis pathways. Overall, these results suggest that phosphorylation-mediated regulation may contribute to inter-individual differences in muscle fiber number and size during early development.