Immunolocalisation of Olfactory Signalling Molecules in Spermatozoa

Abstract

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.