Fig. 2. Rhomboid expression in the tip cell lineage. (A,B) Embryos of the genotype asense-Gal4 x UAS-nlacZ and stained for ß-galactosidase reveal expression in the tip mother cell at early stage 11 (arrowhead in A) and in both its daughters at stage 12 (arrowheads mark the tip and sibling cell in B). (C,D) Tubules from A37 embryos in which ß-gal (green) is expressed under the regulation of the neuromusculin enhancer, stained with an antibody against Rhomboid (red). At stage 11, ß-gal (arrowheads indicate tip mother cells) and Rho (arrows) are weakly expressed in the tip mother cells (C) and more strongly in both daughters from stage 12 onwards (D, stage 13: arrowheads, ß-gal; arrows, Rho). (E,F) In numb mutants (E) or if an activated N construct, N^intra is expressed in the tip mother cell using asense-Gal4 (F), the TC is lost. Instead, two SCs are specified and remain fully integrated in the tubule epithelium [arrowheads and marked by ß-gal (green) in E]. Rho (red) is expressed in both SCs. (G,H) In embryos mutant for the proneural (G) or neurogenic (H) genes TC specification is disrupted. (G) In embryos lacking the AS-C, the tubules (labelled for Cut in green) develop without tip and sibling cells and lack Rho, even though it is expressed in the midline (arrow in the inset). (H) In embryos mutant for N, the whole proneural cluster develops into TCs (eight to 12 cells in each tubule, labelled for Ac in green) and all these cells express Rho (red). aMT, anterior; pMT, posterior Malpighian tubule.