Fig. 1. PcG mutant neuroblast lineages fail to proliferate. Confocal images of late third-instar nervous system immunostained for Cyclin E (CYC E), phosphohistone H3 (PH3) and nuclear ß-galactosidase (nLACZ) in positively labeled MARCM clones. All panels show z projections of image stacks recorded on the ventral side. (A) Ventral view of a whole-mount nervous system showing a large number of mitotic cells in the optic lobes (OL) and in discrete foci evenly distributed in the central brain (CB) and in the thoracic part (T) of the ventral ganglia (VG), but not in the abdominal region (A). (B-E) Mitosis in isolated wild-type neuroblast lineages is revealed by PH3 staining in a maximum of two cells: the large neuroblast (asterisk) and/or the closely associated GMC (arrowhead) at the frequency indicated for each panel (n=148). In B, mitotic activity is seen outside of the clone. In C, mitotic activity is seen in the neuroblast. In D, mitotic activity is seen in the GMC. In E, mitotic activity is seen in neuroblast and GMC. (F-I) Compared with wild-type MARCM neuroblast clones in the central brain (F) or the ventral ganglia (H), Sce mutant clones in the same areas (G,I) contain a much smaller number of nuclei and do not stain for PH3. The dotted lines in F,G demarcate optic lobe (OL) and central brain (CB) by the density of mitotic cells. (J) The percentage of mitotic Sce and other PcG mutant clones is plotted with the number of clones examined indicated in parentheses. For genotypes, see Materials and methods. Scale bars: A, 50 µm; B-E, 5 µm, F-I, 30 µm.