Human sperm chemotaxis is a critical component of the fertilization process, but the molecular basis for this behavior remains unclear. Recent evidence shows that chemotactic responses depend on activation of the sperm olfactory receptor, hOR17-4. Certain floral scents, including bourgeonal, activate hOR17-4, trigger pronounced Ca 2؉ fluxes, and evoke chemotaxis. Here, we provide evidence that hOR17-4 activation is coupled to a cAMP-mediated signaling cascade. Multidimensional protein identification technology was used to identify potential components of a G-protein-coupled cAMP transduction pathway in human sperm. These products included various membrane-associated adenylate cyclase (mAC) isoforms and the G olf -subunit. Using immunocytochemistry, specific mAC isoforms were localized to particular cell regions. Whereas mAC III occurred in the sperm head and midpiece, mAC VIII was distributed predominantly in the flagellum. In contrast, G olf was found mostly in the flagellum and midpiece. The observed spatial distribution patterns largely correspond to the spatiotemporal character of hOR17-4-induced Ca 2؉ changes. Behavioral and Ca 2؉ signaling responses of human sperm to bourgeonal were bioassayed in the presence, or absence, of the adenylate cyclase antagonist SQ22536. This specific agent inhibits particulate AC, but not soluble AC, activation. Upon incubation with SQ22536, cells ceased to exhibit Ca 2؉ signaling, chemotaxis, and hyperactivation (faster swim speed and flagellar beat rate) in response to bourgeonal. Particulate AC is therefore required for induction of hOR17-4-mediated human sperm behavior and represents a promising target for future design of contraceptive drugs.

Multiple trials failed to express significant amounts of olfactory receptors in heterologous cells as they are typically retained in the endoplasmic reticulum (ER). Evidence is accumulating that cell-type-specific accessory proteins regulate the folding of olfactory receptors, their exit from the ER, and the trafficking to the plasma membrane of the olfactory cilia where the receptors gain access to odorants. We found Hsc70t, a testis-enriched variant of the Hsp70 family of heat shock proteins which is specifically expressed in post-meiotic germ cells, in the olfactory epithelium of mouse and human. Cotransfected HEK293 cells with Hsc70t and different green fluorescent protein-tagged odorant receptors (ORs) from mouse and man showed a significantly enhanced OR expression. Hsc70t expression also changed the amount of cells functionally expressing olfactory receptors at the cell surface as the number of cells responding to odorants in Ca2+-imaging experiments significantly increased. Our results show that Hsc70t helps expression of ORs in heterologous cell systems and helped the characterization of an "orphan" human olfactory receptor.

A growing number of proteins originally found in endocytic structures of the plasma membrane appear to be able to traffic into the nucleus, but the cellular function of this translocation remains unclear. We have found that β-arrestin2, which typically shows a cytoplasmic localization owing to constitutive nuclear export, appears in the nucleus after stimulation of the G-protein-coupled odorant receptor hOR17-4. In the nucleus, β-arrestin2 was involved in transcriptional regulation as shown by a Gal4-based transactivation assay. Moreover, we discovered that β-arrestin2 and hOR17-4, a receptor known to have a role in sperm-egg communication, colocalize in the midpiece of mature human spermatozoa. Stimulation of hOR17-4 in spermatozoa induced PKA-dependent translocation of β-arrestin2 to the nucleus and nuclear accumulation of phosphorylated MAPKs. Analysis of the interaction partners of β-arrestin2 indicates that odorant receptor signaling in spermatozoa may be important for the regulation of gene expression during the early processes of fertilization.

The olfactory system is exposed to a plethora of chemical compounds throughout an organism's lifespan. Anticipation of stimuli and construction of appropriate neural filters present a significant challenge. This may be addressed via modulation of the protein composition of the sensory epithelium in response to environmental conditions. To reveal the mechanisms governing these changes, we employed a comprehensive quantitative proteomics strategy. Two groups of juvenile mice were treated with either pulsed or continuous application of octanal. After 20 days of treatment, we performed a behavioral study and conducted electrophysiological recordings from the olfactory epithelium (OE). Both treated groups demonstrated peripheral desensitization to octanal; however, only the 'continuous' group exhibited habituation. To obtain novel insight into the molecular mechanisms underpinning the peripheral desensitization to octanal, the OE proteomes of octanal-treated mice versus control were quantitatively analyzed using two-dimensional difference gel electrophoresis. We identified several significantly regulated proteins that were functionally classified as calcium-binding proteins, cytoskeletal proteins, and lipocalins. The calcium-binding proteins and cytoskeletal proteins were up-regulated in the 'pulsed' group, whereas in the 'continuous' group, four lipocalins were significantly down-regulated. Uniquely, the lipocalin odorant-binding protein Ia was drastically down-regulated in both groups. The identified proteins reflect changes throughout the entire OE, corresponding to changes in neuronal, non-neuronal, and pericellular processes. We report the regulation of several promising candidates for the investigation of odorant-induced changes of the OE. Among these proteins are different lipocalins, which seem to play a crucial role in the regulation of the sensitivity of the olfactory system.

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