In mice, social behavior is driven by pheromones that encode
information related to age, sex, and physiological state. While mice exhibit
different social behaviors towards adults, juveniles, and neonates such that
adult male mice never initiate copulation with immature females, sensory cues
that enable specific recognition of juvenile mice are unknown. The Touhara
group and co-workers in the University of Tokyo in collaboration with groups in
Harvard University and RWTH Aachen University discovered a juvenile pheromone
produced by young mice before puberty, termed exocrine-gland secreting peptide
22 (ESP22). ESP22 is a 10 kDa protein that is secreted from the lacrimal gland
and released into tears of 2-3 week old mice. ESP22 activates high affinity
sensory neurons in the vomeronasal organ, and downstream limbic neurons in the
medial amygdala. Recombinant ESP22, painted on mice, exerts a powerful
inhibitory effect on adult male mating behavior.