Max-Planck-Institut für biophysikalische Chemie, Abt. 170, D-37018 Göttingen,
The Malpighian tubules, which are the insect kidneys, provide a simple model system to study cellular processes underlying neurogenesis and organogenesis. During embryonic development of Drosophila, the tubules evert as four separate outbuddings of the ectodermal hindgut primordium. Their elongation is controlled by a single cell at the ending of each tubule, the tip cell. This cell arises by division of a tip mother cell which is selected from a group of equivalent cells expressing achaete, scute and lethal of scute via lateral inhibition through Notch and Delta activities. In the neurogenic mutants supernumerary tip cells appear and in mutants for proneural genes the tip cells are absent and the cell number in the tubules is drastically reduced. Once a tip mother cell has divided, the segregating tip cell controls proliferation in the tubule most likely by sending out a mitogenic signal to its neighbours (Skaer, 1989). In parallel the tip cells differentiate into neural cells, begin to express synaptic vesicle proteins like synaptotagmin and finally connect to the peripheral nervous system during late embryogenesis (Hoch et al., 1994). We speculate that the tip cell might serve as an osmosensor controlling the excretory function of the Malpighian tubules. We have identified a novel locus which we named double stalk that is required in the tip cells of the Malpighian tubules for neural differentiation and proliferation control. A candidate gene in the double stalk locus that codes for a kinase activator protein expressed in the Malpighian tubules will be presented.
Skaer (1989). Nature 342, 566-569.
Hoch et al. (1994). Development 120, 3439-3450.