Fig. 6. Loss of chn function leads to decreased expression of sc and enhancer-lacZ constructs, and can impede SOP formation. All figures show parts of third instar wing disks. Except in D, clones homozygous for chn^ECJ1 are marked by the absence of green. Anti-Sens antibody marks emerged SOPs (blue channel). (A) Clone that includes part of the DC proneural cluster. The mutant cells accumulate less Sc protein (red channel) and give the clone a split appearance. The Sens marker has just started making discernable the SOP of the posterior DC macrochaetae (arrowhead). (B) A large mutant clone that includes the anterior part of a DC proneural cluster (arrowhead), as revealed by expression of the AS1.4DC-lacZ construct (red). (C) Higher magnification image of the same DC cluster, showing merged, green, and red plus blue channels. Most of the cells with strong accumulation of ß-galactosidase and the PDC SOP are in the heterozygous territory. The cluster appears roundish rather than elongated (Fig. 5A,F) because there is little accumulation of ß-galactosidase in the homozygous territory (arrowhead). (D) Cells of a DC proneural cluster that overexpress UAS-chni^S (green) accumulate less Sc protein than neighboring cells (red channel). (E) An SOP has been singled out from an heterozygous chn^ECJ1 cell (arrowhead). (F) Clone that includes part of the L3 proneural cluster, as revealed by the expression of the L3-TSM-lacZ construct. Note the irregular shape of the cluster and the reduced expression within the homozygous territory (arrowhead). A control proneural cluster entirely within heterozygous territory has a roundish shape (G). (H) Merged and red plus blue channels views of the notum region of a late third instar wing disk harboring several clones of homozygous chn^ECJ1 cells. Sc (red) and Sens (blue) stainings reveal SOPs. The PSC SOP, which would have to develop within a clone (arrow) and is one of the earliest SOPs to emerge, is absent. Nomenclature for other SOPs is indicated. The presence of the ADC SOP confirms the late stage of the disk.