Researchers have found that a human olfactory receptor protein previously shown to act in sperm, where it appears to help guide sperm to the egg during fertilization, is also expressed in human olfactory tissues in the nose and functions in our sense of smell. This remarkable dual capacity marks a functional range previously unknown for mammalian olfactory receptor proteins.
From Cell Press:
Talented sniffer: A receptor known for guiding sperm to egg plays a role in the nose
Having sperm successfully locate the egg is a crucial step in fertilization. Recent evidence had shown that hOR17-4, a human olfactory receptor protein that is unconventionally expressed on sperm cells, appears to play a key role in sperm-egg communication and chemotaxis prior to gamete encounter. Whether this “sperm” olfactory receptor is restricted to reproductive functions or acts bi-functionally in the context of conventional olfaction has been a longstanding question.
In their current study, a team of researchers including Marc Spehr of the University of Maryland and Katlen Schwane of Ruhr-University Bochum, Germany, addressed this question by using a number of experimental approaches.
They demonstrated the expression of hOR17-4 in the human nose by using standard molecular techniques, whereas they tested and demonstrated the actual function of the receptor in a simple “sniffing test” as well as with electrical recordings from nasal sensory tissue (by electro-olfactogram). The findings show that, interestingly, the basic receptor function of hOR17-4 seems to be identical in both human sperm and olfactory neurons. In light of their findings, the authors propose a model in which a single receptor protein helps perform diverse chemosensory functions in the nose as well as in sperm.
It is tempting to speculate that in the future, “sniffing tests” could be employed as a diagnostic tool for fertility defects associated with olfactory receptor-dependent chemotaxis in sperm.