Fig. 7. Partial restoration of brain tracts in cell death prevented vnd mutant. Laser confocal microscopy of stage 15 embryos, reconstructions of optical sections, lateral views. Arrows indicate tritocerebral region. (A,B) Wild-type; (C,D) vnd mutant; (E,F) sca::Gal4/UAS::p35 in vnd-null mutant background. Embryos in B,D,F are not the same as in A,C,E, respectively. (A,C,E) Embryonic brain immunolabelled with anti-FAS2 (red). (B,D,F) Embryonic brain double-immunolabelled with anti-FAS2 (red) and anti-ELAV (green). (A,B) In wild type, FAS2 immunostaining reveals a number of early differentiating neurons as well as axon tracts, and ELAV expression is apparent within postmitotic neurons of all brain neuromeres, including the tritocerebrum. (C,D) By contrast, in vnd-null mutants, a gap is seen in the area of the tritocerebral region and the majority of ELAV-expressing cells are lacking in this domain. (E,F) Ubiquitous block of apoptosis partially restores the gap-like defects observed in vnd loss-of-function mutants: FAS2-immunoreactive longitudinal connectives are detectable, although neural fibres display fasciculation defects, and a significant number of ELAV-expressing cells are detectable in the cell death prevented vnd mutant tritocerebrum (F, arrow; compare with B).