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

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.

This study aimed to investigate the differential expression patterns and polymorphisms in PAPPA2 gene across diverse sheep breeds and their association with litter size.

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.

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.

The g.55924884C>G polymorphism in PAPPA2 gene significantly influences ovine litter size and may serve a genetic marker for selective breeding.