Fig. 1. brat mutation perturbs development of the larval central brain. GAL4^NP3262 driven UAS-mCD8::GFPexpression in heterozygous (A,C,E) and homozygous (B,D,F) zygotic brat mutant larval CNS reveals all cell membranes of secondary lineages in central brain (CB) and optic lobe (OL). (A,B) In late third instar brat mutant larvae, brain hemispheres (Br) are markedly enlarged and characterized by cellular overgrowth whereas ventral ganglia (VG) appear normal (compare B with A). (C,D) In early to mid third instar larvae, brain hemispheres of brat mutants appear of same size as heterozygous brain hemispheres when viewed as whole mounts (D, compare with C). The cellular architecture of optic lobes is unaltered but is pushed aside by overgrowth of the central brain area that displays abnormal cells types. (E) Higher magnification of heterozygous central brain area in C reveals a regular pattern of large superficial neuroblasts (asterisks), in association with smaller numerous progeny cells. (F) By contrast, higher magnification of central brain area in D reveals that brat mutant brain tissue is characterized by dense cellular masses of numerous small, pleiomorphic cells in addition to larger cells, presumably neuroblasts (asterisks). Scale bar, 70 µm. Genotypes: (A,C,E) brat¹¹, GAL4^NP3262/FRT40A; UAS-mCD8::GFP^LL6, UAS-nlslacZ^J312/+. (B,D,F) brat¹¹, GAL4^NP3262/FRT40A, brat¹¹; UAS-mCD8::GFP^LL6, UAS-nlslacZ^J312/+.