The long-range goal of this research project is to understand the instructions carried by an animal's genes that make some cells excitable (like nerve and muscle cells) and other cells unexcitable (like gut and skin cells). The genes not only carry instructions on how to make special proteins (channels) that create the electrical currents (signals) in cells, but also instructions on which cells should make these channels and additional instructions to make other proteins that modify (modulate) the channel's function. The studies will focus on the fruit fly Drosophila because it has both an organized nervous system, similar to the human nervous system in many ways, and its genes have been well studied and are easy to manipulate. All of the studies will be done on Drosophila nerve or muscle cells taken from embryos and grown in culture dishes, where they can be studied by electrical techniques that allow direct measurement of the function of the channels. The first set of studies will involve the channels that carry either calcium ions or potassium ions. These channels are especially interesting because they determine how many calcium ions enter the cell, which determines how strongly a muscle contracts and how much neurotransmitter is released by a nerve to excite neighboring cells. The techniques used allow the study of single channels. The number of different types of channels and the properties of each will be determined (how they respond to voltage, how many ions they transport, etc.) The second set of studies will determine if the function of these channels can be modified by neurotransmitters applied to the outside of the cells or "second messengers" inside the cells. Current theories of learning hypothesize that learning involves modulation of channel function by external and internal messengers. Drosophila mutants have been isolated that are poor learners and are missing particular proteins that control second messengers. These mutants will be used to explore modulation mechanisms. The third set of studies will use the results of the first two sets of studies to identify genes that control the channels in nerve and muscle cells. Mutations which alter the animal's behavior will be studied to determine if they alter channel function. Since these behavioral mutants can be mapped, the altered genes are identified. If the mutant gene alters channel function, the gene will be identified as one that codes for a channel, for a protein that modulates a channel, or for a protein that determines the expression of a channel. Channel-related genes will not only be found from studies of behavioral mutants, but also from studies of deletions, individuals missing a small region of a chromosome. Although these deletions are usually lethal to the animal, their effect on channels can be studied in cultured cells.
