Abstract
A unique characteristic of mammalian sperm thermotaxis is extreme temperature sensitivity, manifested by the capacity of spermatozoa to respond to temperature changes of <0.0006 °C as they swim their body-length distance. The identity of the sensing system that confers this exceptional sensitivity on spermatozoa is not known. Here we show that the temperature-sensing system of mammalian spermatozoa involves opsins, known to be G-protein-coupled receptors that act as photosensors in vision. We demonstrate by molecular, immunological, and functional approaches that opsins are present in human and mouse spermatozoa at specific sites, which depend on the species and the opsin type, and that they are involved in sperm thermotaxis via two signalling pathways—the phospholipase C and the cyclic-nucleotide pathways. Our results suggest that, depending on the context and the tissue, mammalian opsins act not only as photosensors but also as thermosensors.
Highlights
Since GPCRs that signal through the activation of PLC are known to lead to the opening of TRPC channels11, we examined whether these channels, found to exist in human spermatozoa12, are involved in sperm thermotaxis
To determine whether PDE is involved in thermotaxis, we studied the effects of the general PDE inhibitors caffeine and 3-isobutyl-1-methylxanthine (IBMX) and the specific PDE5/6 inhibitor sildenafil44 on human sperm thermotaxis, expecting to see partial inhibition if the cyclic-nucleotide pathway is involved in parallel to the PLC pathway
We studied several of them and showed that they are present in mammalian spermatozoa and involved in sperm thermotaxis
Summary
The anti-neuropsin antibody detected a band at the expected molecular size of the monomeric and dimeric forms of this opsin both in mouse and human spermatozoa (Fig. 2h). Hydroxylamine added with 400 nm laser illumination (which excites blue opsin, encephalopsin, melanopsin and neuropsin) or with 560 nm laser illumination (which excites rhodopsin as well as green and red opsin) significantly reduced sperm accumulation (Fig. 4a, right columns) without affecting the motility relatively to hydroxylamine added in the dark (Table 1).
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