Abstract
Background
Olfactory receptor (OR) genes are highly polymorphic and form extensive families that recognize a wide range of vertebrate odorants. Although OR gene clusters are dispersed across many regions of vertebrate genomes, ORs expressed in the testes exhibit major histocompatibility complex (MHC)-linked structural conservation.
Results
In this study, we selected nine MHC-linked OR genes based on their expression levels in pig testes and developed a sequence-based typing method for these genes. We then performed high-resolution typing of these OR genes, along with three major classical MHC class I genes (SLA-1, -2, and − 3), in 48 pigs across six breeds. We observed significantly higher allelic diversity (P < 0.01) in ORs with strong linkage disequilibrium (LD) to SLA compared to those with weak or no LD, and we identified 48 SLA class I-OR haplotypes using the expectation-maximization algorithm. The genetic diversity of SLA-linked ORs was positively correlated with their expression levels in the testis. Specifically, SLA-linked ORs with higher testicular expression (FPKM ≥ 0.1) exhibited an increase in the number of codons under mutually diversifying selection with SLA compared to those with lower expression (FPKM < 0.1).
Conclusions
Our results suggest the presence of evolutionary interactions between the MHC and linked OR genes. These characteristics of SLA-linked ORs support the potential involvement of MHC-linked ORs in MHC-based mate selection.