FUNCTIONAL DOMAINS ARE SPECIFIED TO SINGLE-CELL RESOLUTION IN A DROSOPHILA EPITHELIUM

Specification of pattern is fundamental to the development of a multic ellular organism. The Malpighian (renal) tubule of Drosophila melanoga ster is a simple epithelium that proliferates under the direction of a single tip cell into three morphologically distinct domains. However, systematic analysis of a panel of over 700 P{GAL4} enhancer trap line s reveals unexpected richness for such an apparently simple tissue. Us ing numerical analysis, it was possible formally to reconcile apparent ly similar or complementary expression domains and thus to define at l east five genetically defined domains and multiple cell types. Remarka bly, the positions of domain boundaries and the numbers of both princi pal and secondary (''stellate'') cell types within each domain are rep roducible to near single-cell precision between individual animals. Do mains of physiological function were also mapped using transport or ex pression assays. Invariably, they respect the boundaries defined by en hancer activity. These genetic domains can also be visualized in vivo, both in transgenic and wild-type flies, providing an ''identified cel l'' system for epithelial physiology. Building upon recent advances in Drosophila Malpighian tubule physiology, the present study confirms t his tissue as a singular model for integrative physiology.