Comprehensive Analysis of PAPPA2 Expression and Genetic Variants in Sheep and Their Association With Litter Size

BACKGROUND: The PAPPA2 gene encodes a metalloproteinase critical for regulating insulin-like growth factor (IGF) bioavailability through cleavage of insulin-like growth factor-binding protein 5 (IGFBP5). While its role in human and murine reproduction is documented, its function in sheep reproductive traits remains underexplored. OBJECTIVE: This study aimed to investigate the differential expression patterns and polymorphisms in PAPPA2 gene across diverse sheep breeds and their association with litter size. METHODS: Genotyping of two single nucleotide polymorphisms (SNPs; g.55757202C>A and g.55924884C>G) was performed in 760 ewes from six breeds. Three high-fertility Small Tail Han ewes and three low-fertility Tibetan ewes were selected for tissue-specific expression analysis. Associations between SNPs and litter size were statistically analysed, and bioinformatics tools were employed to assess structural impacts of mutations. RESULTS: The g.55924884C>G SNP exhibited a significant association with litter size in Small Tail Han sheep across parities (p < 0.05). qPCR revealed markedly higher PAPPA2 expression in low-fertility Tibetan sheep ovaries compared to high-fertility Small Tail Han sheep (p < 0.05). Bioinformatics analysis indicated that the g.55924884C>G mutation induced substantial alterations in the secondary and tertiary structures of PAPPA2 protein, while g.55757202C>A had minimal structural impact, which may be the reason for the change in litter size caused by the g.55924884C>G mutation. CONCLUSIONS: The g.55924884C>G polymorphism in PAPPA2 gene significantly influences ovine litter size and may serve a genetic marker for selective breeding.