Rhodopsin and melanopsin coexist in mammalian sperm cells and activate different signaling pathways for thermotaxis

Recently, various opsin types, known to be involved in vision, were demonstrated to be present in human and mouse sperm cells and to be involved there in thermosensing for thermotaxis. In vision, each opsin type is restricted to specific cells. The situation in this respect in sperm cells is not known. It is also not known whether or not both signaling pathways, found to function in sperm thermotaxis, are each activated by specific opsins, as in vision. Here we addressed these questions. Choosing rhodopsin and melanopsin as test cases and employing immunocytochemical analysis with antibodies against these opsins, we found that the majority of sperm cells were stained by both antibodies, indicating that most of the cells contained both opsins. By employing mutant mouse sperm cells that do not express melanopsin combined with specific signaling inhibitors, we furthermore demonstrated that rhodopsin and melanopsin each activates a different pathway. Thus, in mammalian sperm thermotaxis, as in vision, rhodopsin and melanopsin each triggers a different signaling pathway but, unlike in vision, both opsin types coexist in the same sperm cells.