Enhancer-promoter loop mediated upregulation of FGF8 drives early rapid testicular development in Erhualian boars

The Erhualian pig, a Chinese indigenous breed with superior reproductive traits, exhibits accelerated testicular development in boars. Comparative analyses with Landrace pigs revealed that upregulated FGF8 expression drives precocious testicular development in Erhualian boars by stimulating Sertoli cell proliferation, significantly advancing the early developmental trajectory. Histological examinations demonstrated accelerated testis growth and earlier spermatogenesis onset in Erhualian pigs versus Landrace controls; subsequent transcriptomic profiling and scRNA-seq data confirmed Erhualian testicular FGF8 upregulation correlating with Sertoli cell proliferation, with germ cell-specific FGF8 expression and Sertoli cell-restricted FGFR1 receptor localization indicating paracrine regulation. Functional validation using organotypic culture of testicular tissue and primary Sertoli cell cultures established that FGF8 supplementation promotes proliferation through the FGF8-FGFR1-MAPK-Cyclin axis, whereas FGFR1 knockdown abrogates this mitogenic effect on testicular development. Mechanistic interrogation via H3K27ac CUT&Tag integrated with epigenomic and 3D chromatin architecture datasets uncovered CTCF-anchored enhancer-promoter loops governing FGF8 transcription. Collectively, we identify FGF8-mediated Sertoli cell expansion as a key determinant of accelerated testicular maturation in Erhualian boars, providing mechanistic insights for livestock genetic improvement and reproductive biology.