circMAPKBP1 functions as a miR-143-y sponge to regulate quail myoblast proliferation and differentiation.

The quail (Coturnix japonica) is an economically important poultry species and a useful avian model for muscle biology. Although circular RNA (circRNA)-miRNA competitive endogenous RNA (ceRNA) networks have been described in chicken and duck skeletal muscle, their roles in quail remain poorly defined. We identified circMAPKBP1, generated from the mitogen-activated protein kinase binding protein 1 (MAPKBP1), as highly expressed in quail skeletal muscle and myoblasts. Gain- and loss-of-function experiments in quail myoblast 7 (QM7) cells showed that circMAPKBP1 promotes proliferation while inhibiting differentiation. Dual-luciferase reporter assays demonstrated direct binding between circMAPKBP1 and miR-143-y. Overexpression of miR-143-y promoted both proliferation and differentiation, and its expression pattern was reciprocal to that of circMAPKBP1 during differentiation. RNA-seq of miR-143-y-overexpressing cells revealed significant enrichment of downregulated genes in the mitogen-activated protein kinase (MAPK) signaling pathway. These results establish, for the first time, that the circMAPKBP1/miR-143-y axis modulates quail myogenesis, with the sponge mechanism most clearly explaining the opposing effects on differentiation. The findings provide molecular targets and a mechanistic framework for genetic improvement of muscle traits in poultry.