Despite the prevalence of mental illness in society, little is known about the basic neural circuitryregulating human behavior. Evidence suggests that mice and humans share the essential neuroanatomyleading to basic behaviors such as aggression and mating. However, unlike humans, these behaviors arethought to be regulated in mice primarily through secreted chemical cues known as pheromones. In order todevelop valuable mouse models to study these conserved neural circuits, it is critical to first understand thechemical ligands that initiate activation of these pathways in the mouse. The objective of this application isto determine the molecular role of a particular class of pheromone binding proteins called Major UrinaryProteins (MUPs) in mediating pheromone signaling between mice. My central hypothesis is that MUPs are acritical component of the pheromone signal excreted by one animal and detected by another. Thishypothesis is based on the following previously published observations as well as my own preliminaryfindings: 1) MUPs are expressed in male urine in different combinations between mice suggesting a role ininformation coding. 2) MUPs contain a central binding pocket which binds known pheromone ligands. 3)Behavioral studies suggest MUPs are involved in certain pheromone-mediated behaviors. 4) My preliminarystudies show that MUP-ligand complexes directly activate VNO neurons in vitro. Based on these findings, itis my working hypothesis that MUPs interact directly as ligands or indirectly as ligand carriers with VNOneurons to effect pheromone signaling. I will test the extent to which MUP-ligand complexes, MUP ligandsalone, and MUPs alone (without ligands) activate VNO sensory neurons by calcium imaging dissociatedVNO neurons. In addition, based on the fact that mice express different combinations of MUPs in their urine,it is my working hypothesis that different MUPs will activate discrete populations of VNO neurons, providinga potential mechanism by which mice can discriminate between conspecifics. I plan to test this workinghypothesis by purifying individual MUPs from urine and comparing their activation specificity by calciumimaging on populations of dissociated VNO neurons. By completing the proposed study, I will havedetermined the exact nature of the MUP protein and ligand interaction with sensory neurons. In addition, Iwill have determined the function of the heterogeneous regulation of MUP expression between mousestrains. Elucidating these mechanisms will provide an important step forward in understanding pheromonesignaling at a molecular level, which will advance our understanding of the downstream molecular pathwaysconserved in humans that regulate basic behaviors.
