Testis
In 1992, ectopic expression of OR-like proteins in dog testis was reported after the OR multigene family was originally isolated from rat olfactory epithelium [7]. Subsequently, many experiments were performed to trace the presence of ORs in animal testicular tissues for the investigation of OR function in sperm-oocyte chemotaxis, where it was thought that ORs should have chemotactic roles during fertilization. Moreover, ORs are also thought to be involved in chemotaxis [74] and cytokinesis [75], and dozens of ORs were found to be expressed in the testis of mammals using deep sequencing [32]. Several tens of ORs were expressed in testicular tissues of mammals, and their roles in sperm-oocyte chemotaxis were investigated. Very recently, Milardi et al. [33] suggested that the presence of ORs, such as OR4S1, OR4C13, and OR1I1, on mature cells might be related to acrosome activity and sperm motility after a proteomic analysis. Itakura et al. [34] also identified Gαolf and several kinds of ORs from rat placenta using RT-PCR, western blotting, and immunochemical methods. They suggested that ORs may recognize some small molecules in the placenta as environmental signals and mediate the growth of the fetus.