Combined-Population GWAS Identifies PROX2 as a Candidate Gene Associated with Total Teat Number Variation in Pigs

Teat number is an important economic trait in pigs because it affects sow reproductive performance and piglet nursing ability, yet its genetic basis and molecular regulatory mechanisms remain incompletely understood. In this study, a combined-population genome-wide association study was performed in Canadian and French Large White pigs to identify loci associated with teat number traits. A total of 4217 pigs were genotyped, and 2,244,684 autosomal single-nucleotide polymorphisms were retained after quality control and genotype imputation. Multiple association signals for total teat number were detected, with major peaks located on chromosomes 7 and 10. Among the positional candidate genes, PROX2 was prioritized for further validation, and genotype–phenotype association analysis showed that pigs with the CC genotype at the PROX2 polymorphic locus had significantly lower total teat number than those with the CT and TT genotypes. To investigate its biological role, PROX2 was silenced in porcine mammary epithelial cells. Transcriptome analysis identified 887 differentially expressed genes after PROX2 knockdown, and functional assays showed that PROX2 silencing inhibited cell proliferation, altered cell cycle progression, and affected the expression of proliferation- and development-related genes. These findings indicate that PROX2 is an important candidate gene associated with teat number variation in pigs.