Expression of olfactory receptors (ORs) in non-olfactory tissues has been widely reported over the last 20 years. Olfactory marker protein (OMP) is highly expressed in mature olfactory sensory neurons (mOSNs) of the olfactory epithelium. It is involved in the olfactory signal transduction pathway, which is mediated by well-conserved components, including ORs, olfactory G protein (Golf), and adenylyl cyclase 3 (AC3). OMP is widely expressed in non-olfactory tissues with an apparent preference for motile cells. We hypothesized that OMP is expressed in compartment-specific locations and co-localize with an OR, Golf, and AC3 in rat epididymal and human-ejaculated spermatozoa. We used immunocytochemistry to examine the expression patterns of OMP and OR6B2 (human OR, served as positive olfactory control) in experimentally induced modes of activation and determine whether there are any observable differences in proteins expression during the post-ejaculatory stages of spermatozoal functional maturation. We found that OMP was expressed in compartment-specific locations in human and rat spermatozoa. OMP was co-expressed with Golf and AC3 in rat spermatozoa and with OR6B2 in all three modes of activation (control, activated, and hyperactivated), and the mode of activation changed the co-expression pattern in acrosomal-reacted human spermatozoa. These observations suggest that OMP expression is a reliable indicator of OR-mediated chemoreception, may be used to identify ectopically expressed ORs, and could participate in second messenger signaling cascades that mediate fertility.

Olfactory receptors (ORs) expressed by mature olfactory sensory neurons (mOSNs) in the olfactory neuroepithelium detect and distinguish volatile chemicals of diverse structure. Chemoreception begins when the odorant binds to the OR, initiating a signal transduction cascade involving olfactory G-protein (Golf), adenylyl cyclase 3 (AC3), and cyclic nucleotide-gated cation channels that eventually results in odour perceptions. ORs are also present in non-olfactory systems including spermatozoa. This study examined the immunolocalisation of olfactory marker protein (OMP), OR6B2 (human OR), Golf and AC3 in spermatozoa. OMP is involved in the olfactory signal transduction pathway and is a marker for mOSNs in the olfactory system and for ORs in non-olfactory systems. If OR-chemosensing is confirmed for spermatozoa, the data would imply involvement with excitability, exocytosis, and chemotaxis. We used immunohistochemistry and microscopic analysis to examine olfactory signalling molecules in testis (rat) and spermatozoa (human, ram, rat). In human spermatozoa, we experimentally induced three modes of activation: control, activation and hyperactivation. Modes of activation affected OMP and OR6B2 co-expression. OMP was staged-expressed in the testis, and co-localised with AC3 in the acrosomal membrane and head of rat sperm. OMP was co-expressed with OR6B2, Golf, and AC3 on the head and tail of human, ram, and rat spermatozoa, implying different drivers and separate domains for target recognition (head) and motor activation (tail). The staining patterns in spermatozoa suggest OR-mediated, chemoreceptive mechanisms that control motility, facilitate the acrosomal reaction for capacitation, and promote fertilisation.