Sexual dimorphism in olfactory signaling

Abstract

What makes males and females behave differently? Although genetic master-regulators commonly underlie physical differences, sexually dimorphic behavior is additionally influenced by sensory input such as olfactory cues. Olfaction requires both ligands for signaling and sensory neural circuits for detection. Specialized subsets of each interact to generate gender-dimorphic behavior. It has long been accepted that males and females emit sex-specific odor compounds that function as pheromones to promote stereotypic behavior. Significant advances have now been made in purifying and isolating several of these sex-specific olfactory ligands. In contrast, the neural mechanisms that enable a gender-dimorphic response to these odors remain largely unknown. However, first progress has been made in identifying components of sexually dimorphic olfactory circuits in both Drosophila and the mouse.

Figure 1. Sexual dimorphism in olfactory signaling

Recent experiments have revealed mechanisms for generating gender-specific behaviors in mice and Drosophila [26••,42••]. (a) ESP1 evokes a mating stance when detected by Trpc2- and VR2p5-expressing VNO neurons of female mice (top). Although males have the same neurons that project to the same glomeruli (bottom), there are gender differences in neural activity in central brain regions (green arrows) in response to ESP1, presumably resulting in the sex-specific behavior. Additionally, in strains of male mice that produce ESP1 endogenously, signal-mediated desensitization may occur (gray line, bottom). BST, bed nucleus of the stria terminalis; Me, medial amygdaloid nucleus; PMCo, posteromedial cortical amygdaloid nucleus; MPA, medial preoptic area; VMH, ventromedial hypothalamus. (b) 11-cis-vaccenyl acetate (cVA), a male-specific Drosophila pheromone, evokes different behaviors when detected by Or67d-expressing olfactory neurons of either sex. In males (bottom), the circuit is patterned by the male-specific isoform of fruitless (Fru^M), the DA1 glomerulus is larger than in females, and the projection neurons have a male-specific arbor (purple).