Dynamic myogenic progression of broiler satellite cells during growth and the regulatory role of bone morphogenetic protein 6.

Satellite cells (SCs) contribute to skeletal muscle hypertrophy and meat yields in broilers. An efficient myogenic process of SCs requires timely-regulated transitions of their cellular states from quiescence to activation and then to differentiation. However, our understanding of these dynamic cellular state transitions during broiler growth and underlying regulatory mechanisms remain limited. We conducted a comprehensive characterization of SCs in Ross 308 broilers from 1 to 42 days post-hatch, using an integrated approach combining in vivo and in vitro analyses with single-nucleus RNA sequencing. The results showed that the ratio of MYOD1+ differentiating SCs decreased with age along with the reduced expression of myogenic regulatory genes, suggesting a decline in myogenic capacity. Consistently, snRNA-seq analysis revealed that the proportion of quiescent SCs increased, while the fractions of proliferating and differentiating SCs decreased during growth. Furthermore, bone morphogenetic protein 6 (BMP6), secreted specifically by the quiescent SCs, acts as a key regulator that maintains SC quiescence and inhibits their activation, accounting for the reduced myogenic differentiation capacity of SCs in the breast muscle of broilers at day 42. In vitro cell culture studies validated that knockdown of BMP6 expression in isolated primary SCs promoted proliferation, differentiation, and myotube formation, while overexpression of BMP6 achieved the opposite effects. Therefore, BMP6 was identified as a key regulatory target for maintaining SC quiescence and inhibiting their activation. These findings further advance our understanding into SCs state transitions during growth and provide a foundation for developing strategies to enhance muscle growth in broilers.