OLFACTORY RECEPTORS ARE DISPLAYED ON DOG MATURE SPERM CELLS

Olfactory receptors constitute a huge family of structurally related G protein-coupled receptors, with up to a thousand members expected. We have shown previously that genes belonging to this family were expres sed in the male germ line from both dog and human. The functional sign ificance of this unexpected site of expression was further investigate d in the present study. We demonstrate that a few dog genes representa tive of various subfamilies of olfactory receptors are expressed essen tially in testis, with little or no expression in olfactory mucosa. Ot her randomly selected members of the family show the expected site of expression, restricted to the olfactory system. Antibodies were genera ted against the deduced amino acid sequence of the most abundantly exp ressed olfactory receptor gene in dog testis. The purified serum was a ble to detect the gene product (DTMT receptor) in late round and elong ated spermatids, as well as in the cytoplasmic droplet that characteri zes the maturation of dog sperm cells, and on the tail midpiece of mat ure spermatozoa. Western blotting further confirmed the presence of a 40-kD immunoreactive protein in the membrane of mature sperm cells. Al together, these results demonstrate that the main expression site of a subset of the large olfactory receptor gene family is not olfactory m ucosa but testis. This expression correlates with the presence of the corresponding protein during sperm cell maturation, and on mature sper m cells. The pattern of expression is consistent with a role as sensor for unidentified chemicals possibly involved in the control of mammal ian sperm maturation, migration, and/or fertilization.