Fig. 4. Grh is required to maintain a large mitotically active neuroblast at late stages. (A-C) Single thoracic MARCM clones marked with n-ßgal driven by elav-GAL4 and labelled for M-phase with H3p. Wild-type clones contain many neurons and the large neuroblast frequently undergoes mitosis at 96 hours (A), whereas grh^B37 homozygous clones contain less neurons and the neuroblast ceases mitosis by 72 hours (B) and is no longer evident by 96 hours (C). (D) Histogram showing that the average number of adult-specific thoracic neurons at 96 hours in grh^B37 clones (n=43 clones, mean=28.6, s.d.=12.7) is approximately half the wild-type value (n=61, mean=57.3, s.d.=15.7).