Yet bombykol is not particularly representative of insect pheromones, much less those found in vertebrates (see Box 1). Nevertheless, research efforts have largely focused on finding analogous monomolecular, sexually dimorphic odour cues in mammals [2]. Such pheromones do exist in laboratory mice and are principally detected by specialised pheromone-sensing neurons in the vomeronasal organ (VNO) of the nose (reviewed

in [4]). The best example is perhaps ESP1, a peptide secreted in the tears of male mice that provokes females to adopt a receptive mating stance (lordosis) [5]. A single vomeronasal receptor (VR, see Box 2) selectively expressed in a small number of vomeronasal sensory neurons (VSNs) is necessary to mediate this behaviour. CAL101 Thus

an elegant model was proposed: a single mammalian sex-pheromone uniquely activates a discrete genetically labelled circuit via its cognate VR, to release a stereotypic fixed action pattern [5]. MK-2206 ic50 If this mechanism extended to the >50 putative peptide pheromones in the mouse genome [4], then highly complex sexual behaviours could be experimentally deconstructed into simpler sub-routines, each driven by a unique genetically encoded signal and mediated by a traceable circuit. In 1959 Bombykol became the first pheromone to be chemically characterised. It is a monomolecular sex-pheromone secreted from glands in the abdomen of the female silk moth, Bombyx mori [3]. Yet in numerous ways it is atypical. Most insect pheromones consist of multi-component blends (reviewed in [2] and [34]). These are significantly more difficult to isolate by fractionation,

such that the strategy used to purify bombykol would likely have failed had it been multi-component. The overt male ‘flutter dance’ behaviour that bombykol provokes is striking, yet many pheromone-mediated responses are not immediately obvious and manifest over longer time frames. These include developmental or physiological processes, such as the induction of puberty [35], and even the inhibition of behaviour [36•]. Sexual dimorphism in pheromone responses are common across the animal kingdom (reviewed in [37]), but how bombykol achieves this may not be. A single pheromone Phosphoglycerate kinase receptor expressed in the antenna of male, but not female months, is sufficient to mediate the behaviour 38 and 39]. Other insect species express sex-pheromone receptors in the antenna of both sexes and route the signal through sexually dimorphic neural circuits to generate different behavioural responses [40••]. Mice, too, display very little sexual dimorphism in the pheromone receptors they express [19]; thus further investigation is required to establish how such males and females respond with opposing behaviours on detection of the same pheromone signal [41]. Vomeronasal receptors (VRs) are among the least understood subfamilies of G protein coupled receptors.