Methods and compositions for modifying fertility and/or spermatogenesis or spermiogenesis in a male mammalian subject involve administering to the subject or contacting the subjects testis cells, germ cells or sperm with a composition that modifies the activation, nucleic acid expression, protein expression, signaling or activity of one or more T1R3 receptors or an intermediate in the signaling pathways thereof in the subjects testis cells or germ cells. In another embodiment, the method further involves administering to the subject or contacting the subjects testis cells, germ cells or sperm with a composition that modifies the activation, nucleic acid expression, protein expression, signaling or activity of G-α-gustducin, or an intermediate in the signaling pathways thereof. Methods for screening a test molecule for its effect on spermatogenesis or spermiogenesis or fertility and compositions for modifying spermatogenesis or spermiogenesis or fertility in a mammalian subject, e.g., contraceptive products, are provided.
