Functional and mechanistic characterization of bone morphogenetic protein 15 (BMP15) in regulating ovarian development in Japanese eel (Anguilla japonica)

The Japanese eel (Anguilla japonica) is a commercially important species whose captive reproduction remains challenging. Bone morphogenetic protein 15 (BMP15) is an oocyte-derived factor that plays a key role in regulating folliculogenesis; however, its function in Japanese eel is unclear. In this study, the full-length Japanese eel bmp15 cDNA was cloned and bioactive recombinant BMP15 protein was produced. Weekly co-administration of recombinant BMP15 with FSH and LHRHa for 10 weeks significantly promoted ovarian development, as indicated by increased gonadosomatic index (GSI), larger oocyte area, and elevated serum vitellogenin (VTG) levels compared to hormone treatment alone. Integrated multi-omics analyses suggested that BMP15 exerts its biological functions through a coordinated regulatory network involving anabolic metabolism, glycerophospholipid biosynthesis, nutrient transport, extracellular matrix remodeling, and suppression of steroidogenesis. These findings are consistent with a mechanistic model in which BMP15 simultaneously promotes growth, maintains follicular homeostasis, and optimizes oocyte quality by controlling maturation timing. Our findings identify BMP15 as a potential key regulator of ovarian development in Japanese eel and highlight its potential as a novel homologous factor for improving artificial maturation strategies in eel aquaculture.