Figure 2

sds22 mutant cells change shape and are extruded from imaginal disc epithelia. Confocal cross-sections through wing discs containing sds22 mutant clones marked by the absence of GFP (A and B) or by the presence of RFP (C). DAPI (blue) marks nuclei. Phalloidin or Armadillo strongly labels apical cell junctions and more weakly labels cell outlines. TOP: A diagram of a wing imaginal disc in cross section. (A) A disc containing a small Minute+ clone of sds22 mutant cells. Mutant cells change shape, shortening along their apical-basal axis and assuming a more cuboidal morphology. In wild-type tissue, nuclei are positioned in a pseudostratified manner, while in mutant tissue nuclei are aligned in a more linear fashion. Note that mutant cells retain correct localisation of the apical adherens junction marker Armadillo. (B) A disc containing several large Minute+ clones of sds22 mutant cells. Mutant cells again shorten to a more cuboidal form with a more linear alignment of nuclei. In addition, several cells have been extruded from the epithelium and are undergoing apoptosis, visible as pyknotic nuclei near the apical or basal surface of the epithelium (arrow). Deep infolding of the mutant tissue causes islands of wild-type tissue to be cut off from surrounding cells. (C) When apoptosis is blocked in sds22 mutant cells by expression of the caspase inhibitor p35, mutant clones (marked by expression of RFP) are still extruded from the epithelium. A ball of mutant cells with no epithelial character has dropped basally from the epithelium.