In Insects, Gustatory Sensory Neurons Project from the Proboscis and Other

Essay

In insects, gustatory sensory neurons project from the proboscis and other structures to the subesophageal ganglion. Interestingly, insects have gustatory sensory neurons that mediate the recognition of water, which is necessary for animals to maintain osmotic homeostasis. Kristin Scott and colleagues have proposed that ppk28, a member of the Degenerin/Epithelial Sodium Channel family, is an osmosensitive ion channel involved in the cellular and behavioral response to water.
A. ppk28 is a predicted ion channel recovered from a microarray screen for genes expressed in the proboscis of wild-type flies but not Poxn^-/- flies (which lack all taste neurons). How could you confirm experimentally that this gene was expressed in gustatory neurons?
B. The experimenters found that about two-thirds of ppk28-expressing neurons were also positive for a marker of water-sensing neurons in taste bristles. Expression of a genetically encoded calcium sensor in ppk28⁺ neurons using the GAL4/UAS system allows visual monitoring of depolarization. What response would you predict from these neurons upon the presentation of aqueous solutions of various concentrations?
C. How would you demonstrate that ppk28 was necessary for a cellular vs. behavioral response to water??