Cell-specific manipulation of second messengers; a toolbox for integrative physiology in Drosophila

Every living cell must detect, and respond appropriately to, external signals. The functions of intracellular second messengers, such as guanosine 3'5'-cyclic monophosphate (cGMP), adenosine 3'5'-cyclic monophosphate (cAMP), and intracellular calcium, are thus intensively studied. However, artifact-free manipulation of these messengers is problematic, and simple pharmacology may not allow selective intervention in distinct cell types in a real, complex tissue. We have devised a method by which second messenger levels can be manipulated in cells of choice using the GAL4/UAS system. By placing different receptors (rat atrial natriuretic peptide [ANP] receptor and Drosophila serotonin receptors [5HT(Dro7) and 5HT(Dro1A)]) under UAS control, they can be targeted to arbitrary defined populations of cells in any tissue of the fly, and second messenger levels can be manipulated simply by adding the natural ligand. The potential of the system is illustrated in the Drosophila renal (Malpighian) tubule, where each receptor was shown to stimulate fluid secretion, to act through its cognate second messenger, and to be blocked by appropriate pharmacological antagonists. The results uncovered a new role for cGMP signaling in tubule and also demonstrate the utility of the tubule as a possible in vivo test bed for novel receptors, ligands, or agonists/antagonists.