Possible roles for products of polymorphic MHC and linked olfactory receptor genes during selection processes in reproduction

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 beta(2)-microglobulin (beta(2)m), were expressed, mainly at the spermatocyte I stage. Of 17 HLA-linked OR genes anal,,zed, 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].