Fig. 2. PcG mutant lineages lack neuronal precursor cells. Confocal images of wild-type control (wt) and Pc mutant MARCM clones labeled with membrane-tethered GFP (CD8::GFP, white) and immunostained as indicated. (A-D) Grh is detectable in the large neuroblasts (arrowheads) of the central brain (CB), but not in the precursor cells of the optic lobes (OL). Elav is expressed in all adult-specific neurons in both areas of the brain hemispheres. A,B are ventral views; C,D are optical cross-sections. Unlike wild-type clones which contain a single neuroblast and a large postmitotic progeny expressing Elav (A,C), the small labeled Pc mutant clones lack Grh-positive nuclei (B,D). Optical cross-sections (C,D) further show that neuronal precursors lie in the outer-most layer (top), and a wild-type neuroblast lineage forms a column spanning the cellular cortex. Pc mutant clones comprise a few neurons loosely associated and located away from the neuroblast layer. (E,F) Mira is evenly detected at the cellular cortex of the large neuroblasts at interphase (PH3-negative, arrowhead). During mitosis, Mira transiently accumulates on one side of the neuroblast forming crescents (PH3-positive, asterisk). The small, labeled mutant Pc clones in F contain only postmitotic cells lacking Mira. (G) The percentage of wt and PcG mutant clones containing Grh- and/or Mira-positive neuronal precursor cells is plotted with the number of clones examined indicated in parentheses. For genotypes see Materials and methods. Scale bars: A,B, 25 µm; C-F, 10 µm.