Wayne A. Johnson, Ph.D.

Professor

University of Washington, 1985, Ph.D.
Harvard Medical School, 1985-89, Postdoc

Research Interests

Molecular mechanisms of sensory signal transduction and the environmental control of innate integrative behaviors
Essentially all organisms have the ability to monitor their external environment through a variety of sensory mechanisms. Innate behavioral responses to altered environmental conditions often involve the integration of multiple sensory modalities. Evolutionary pressures driven by a distinct survival advantage have lead to diverse but nearly universal integrative behaviors directed toward maintenance of close physical association with an abundant food source. Although utilized primarily to provide a reliable source of nutrition, food-associated behavioral plasticity can also play a major role in key developmental transitions. Behavioral responses to food are normally elicited in response to sensory parameters such as temperature, odor, oxygen levels and specific nutrients that have been associated with a food source. These behaviors are an excellent genetic model for understanding sensory integration and the molecular mechanisms of sensory signal transduction. We are utilizing genetic, molecular and physiological approaches to examine sensory mechanisms regulating a key behavioral and developmental transition in Drosophila larvae. During the third and final instar, a larva must stop feeding, purge its gut of food and exit the food source to search for a pupariation site. This characteristic reversal in food-associated behavior, initiated midway through the third instar and essential to survival of the puparium, is referred to as wandering behavior. The physiological trigger responsible for developmental timing of this transition is not well understood. We have identified a small subset of peripheral sensory neurons known as the class IV multiple dendritic(mdIV) neurons that are required for this behavioral transition. This requires mdIV-specific expression of Pickpocket1(PPK1), a Drosophila degenerin/epithelial sodium channel subunit. Results suggest that the mdIV neurons utilize PPK-dependent mechanisms to sense the physical contact with food and to orient their body position appropriately during feeding. We are currently using genetic and molecular techniques to characterize the molecular and physiological mechanisms of sensory signal transduction in mdIV neurons and how these signals are used to modify behavior.

Representative References

1. Liu, L., Yermolaieva, O., Johnson, W.A., Abboud, F.M. and M.J. Welsh (2003) Identification and function of thermosensory neurons in Drosophila larvae. Nature Neuroscience 6: 267-273.

2. Liu, L., Leonard, A.S., Motto, D.G., Feller, M.A., Price, M.P., Johnson, W.A. and M.J. Welsh (2003) Contribution of Drosophila DEG/ENaC genes to salt taste. Neuron 39: 133-146.

3. Ainsley, J.A., Pettus, J.M., Bosenko, D., Gerstein, C.E., Zinkevich, N., Anderson, M.G., Adams, C.M., Welsh, M.J. and W.A. Johnson (2003) Enhanced locomotion caused by loss of the Drosophila DEG/ENaC protein, Pickpocket1. Current Biology 13: 1557–1563.