13 The Dog Olfactory and Vomeronasal Receptor Repertoires

Abstract

During the course of evolution, animals have developed several sensory systems that allow them to communicate with the external world. Olfaction allows them to sense odorant molecules and diverse pheromones that enable them to identify prey, dangers, and potential mates. It involves a complicated process in which volatile molecules are first detected through their specific binding to specialized receptors (Buck and Axel 1991; Buck 2000; Firestein 2001). Two organs, the main olfactory and the accessory olfactory organs, have been anatomically described in most mammals, except in primates, which are devoid of the accessory organ (Giorgi and Rouquier 2002; Young et al. 2005). The main olfactory organ is specialized in the identification and recognition of odorants. The accessory organ identifies pheromones (Bargmann 1997) and plays a specific role in behavior among individuals of the same species. In the two systems, specialized neurons express at their surfaces G-protein-coupled receptors that belong to the superfamily of seven-transmembrane-domain proteins. In human and rodent, the receptors of the main olfactory system, termed ORs, are encoded by the largest gene family (1000–1500 copies) (Buck and Axel 1991; Malnic et al. 2004), whereas receptors of the vomeronasal system, termed VRs, do not exceed about 200 (Giorgi and Rouquier 2002; Young et al. 2005).

The availability of sequence data derived from survey sequencing of DNA from a poodle (Kirkness 2003), and of the 7.5× shotgun sequence of DNA from a boxer (K. Lindblad-Toh, in prep.), allowed the recognition of most, if not all, of the ORs and...