Genetic Mechanisms Shaping the Evolution of an Ancient Myostatin Promoter/enhancer Across Bony Vertebrates

Mutations in Myostatin ( MSTN ) coding-region are known to dramatically enhance muscle mass. In contrast, the impact of variations in MSTN cis-regulatory elements remains poorly understood. To shed light on this issue, we analysed the MTSN promoter/enhancer ( MSTN P/E) using a phylogenetic framework, focused on comparing transcription factor binding site (TFBS) patterns across vertebrates. We identified a conserved core shared by all bony vertebrates, which arose in the MSTN P/E before the Actinopterygii-Sarcopterygii divergence. Within this core, we found clade-specific TFBS arrangements. In addition, we detected an ancient duplication of the MSTN P/E core, which generated additional layers of TFBS conservation across amniotes. The genetic mechanisms driving diversification in the core and duplicated regions include TFBS gain/loss, turnover, and overlapping. Notably, distinct MSTN expression in chicken and mouse embryos somites appears to correlate with structural variations in the MSTN P/E, suggesting adjustments in MSTN expression. Finally, we observed signatures of accelerated evolution in the stem branches of Sauropsida and Mammalia and in the branches leading to Aves, Rodentia and Chiroptera. Our work enables future studies to explore how variations in MSTN P/E may be linked to skeletal muscle trait variation and evolutionary innovation.