Evolution of Odorant Receptors Expressed in Mammalian Testes

Corresponding author: Jon Seger, Department of Biology, University of Utah, 257 S. 1400 East, Salt Lake City, UT 84112-0840., seger{at}bionix.biology.utah.edu (E-mail)

Communicating editor: S. YOKOYAMA

About 10% of mammalian odorant receptors are transcribed in testes, and odorant-receptor proteins have been detected on mature spermatozoa. Testis-expressed odorant receptors (TORs) are hypothesized to play roles in sperm chemotaxis, but they might also be ordinary nasal odorant receptors (NORs) that are expressed gratuitously in testes. Under the sperm-chemotaxis hypothesis, TORs should be subject to intense sexual selection and therefore should show higher rates of amino acid substitution than NORs, but under the gratuitous-expression hypothesis, TORs are misidentified NORs and therefore should evolve like other NORs. To test these predictions, we estimated synonymous and nonsynonymous divergences of orthologous NOR and TOR coding sequences from rat and mouse. Contrary to both hypotheses, TORs are on average more highly conserved than NORs, especially in certain domains of the OR protein. This pattern suggests that some TORs might perform internal nonolfactory functions in testes; for example, they might participate in the regulation of sperm development. However, the pattern is also consistent with a modified gratuitous-expression model in which NORs with specialized ligand specificities are both more highly conserved than typical NORs and more likely to be expressed in testes.

This article has been cited by other articles:

				S. S. Steiger, A. E. Fidler, and B. Kempenaers Detection of Olfactory Receptor Transcripts in Bird Testes J. Hered., June 20, 2008; (2008) esn051v1. [Abstract] [Full Text] [PDF]

				R. D. Emes, S. A. Beatson, C. P. Ponting, and L. Goodstadt Evolution and Comparative Genomics of Odorant- and Pheromone-Associated Genes in Rodents Genome Res., April 1, 2004; 14(4): 591 - 602. [Abstract] [Full Text] [PDF]

				C. Amadou, R. M. Younger, S. Sims, L. H. Matthews, J. Rogers, A. Kumanovics, A. Ziegler, S. Beck, and K. Fischer Lindahl Co-duplication of olfactory receptor and MHC class I genes in the mouse major histocompatibility complex Hum. Mol. Genet., November 15, 2003; 12(22): 3025 - 3040. [Abstract] [Full Text] [PDF]

				A. Volz, A. Ehlers, R. Younger, S. Forbes, J. Trowsdale, D. Schnorr, S. Beck, and A. Ziegler Complex Transcription and Splicing of Odorant Receptor Genes J. Biol. Chem., May 23, 2003; 278(22): 19691 - 19701. [Abstract] [Full Text] [PDF]

				J. M. Young and B. J. Trask The sense of smell: genomics of vertebrate odorant receptors Hum. Mol. Genet., May 15, 2002; 11(10): 1153 - 1160. [Abstract] [Full Text] [PDF]