PROBLEM: Polymorphic genes of the human major histocompatibility complex [MHC; human leukocyte antigen (HLA)] are probably important in determining resistance to parasites and avoidance of inbreeding. We investigated whether HLA-associated sexual selection could also involve HLA-linked olfactory receptor (OR) genes, which might not only participate in olfaction-guided mate choice, but also in selection processes within the testis.
METHOD OF STUDY: The testicular expression status of HLA class I molecules (by immunohistology) and HLA-linked OR genes (by transcriptional analysis) was determined.
RESULTS: Various HLA class I heavy chains, but not β2-microglobulin (β2m), were expressed, mainly at the spermatocyte I stage. Of 17 HLA-linked OR genes analyzed, eight were found to be transcribed in the testis. They exhibited varying numbers of 5′- or 3′-non-coding exons as well as differential splicing.
CONCLUSIONS: We suggest that testis-expressed polymorphic HLA and OR proteins are functionally connected and serve the selection of spermatozoa, enabling them to distinguish `self' from `non-self' [the sperm-receptor-selection (SRS) hypothesis].