Arginine shapes growth and mTOR pathway gene expression in Japanese quails (Coturnix japonica).

Arginine is a crucial amino acid that regulates growth, metabolism, and cellular homeostasis through nutrient-sensing pathways such as the mechanistic target of rapamycin (mTOR). However, the mechanisms by which dietary arginine modulates mTOR signalling and associated gene networks during early development remain poorly understood in birds. Here, we tested the effects of dietary arginine levels (low, control, and high) on body mass, gene expression, and gene network connectivity in Japanese quail chicks (Coturnix japonica). Using 153 birds over a 14-day experiment, we show that post-hatch arginine restriction significantly impairs growth in both sexes, while gene expression and gene network connectivity responses to arginine availability are strongly sex-specific. Arginine supplementation in females led to coordinated upregulation of growth-related genes (IGF1, GHR), translation regulators (EIF4EBP1), lipid metabolism genes (FASN, FABP1), and oxidative defence (SOD2). In contrast, males showed more limited changes, primarily involving MTOR and autophagy-related gene ATG5. Gene network analysis revealed enhanced connectivity and centrality in females under arginine supplementation, suggesting a more extensive gene interaction response, while males showed sparser networks under restriction, with MTOR and IGF1 emerging as key regulatory hubs. These findings provide novel insights into the sensitivity of developing birds to early nutritional conditions and suggest that the mechanisms underlying growth, gene expression, and gene networking can differ between the sexes, even without sex differences in phenotypic traits. Our results highlight the importance of considering sex-specific gene regulatory architectures when evaluating nutritional effects on vertebrate development.