Abstract

Litter size is an important economic trait in the swine industry, and increasing the number of piglets born is a key objective in pig breeding. The Erhualian pig, known for its exceptional prolificacy, has been reported to harbor a quantitative trait locus (QTL) for litter size on porcine chromosome 12 (SSC12). Through fine mapping of this QTL, RPS6KB1 was identified as a promising candidate gene associated with litter size in Erhualian pigs. Immunohistochemical analysis demonstrated that the p70S6K protein is predominantly expressed in the theca cells of Erhualian pig ovaries. Functional analyses revealed that p70S6K regulates androgen synthesis via the LH-responsive PI3K/Akt/mTOR/HSD3B1 signaling pathway and promotes follicular angiogenesis by activating the PI3K/Akt/mTOR/S6/HIF-1α/VEGFA axis. A single nucleotide polymorphism (rs325845933) located in the 3′ untranslated region (3’UTR) of RPS6KB1 was identified, which binds to ssc-miR-7135-5p and modulates RPS6KB1 expression. Association analysis showed that rs325845933 is significantly associated with litter size in Erhualian, American Large White, and Canadian Large White pigs. These results suggest that rs325845933 is a putative functional variant affecting prolificacy and may serve as a valuable molecular marker for improving litter size in pig breeding programs.