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Fig. 2. Grh regulates neural proliferation in a segment-specific manner. (A) Cartoon showing the distribution of neuroblasts (circles) in the postembryonic CNS; the thorax and central abdomen are boxed. The major domains of expression of the Hox genes Antennapedia (Antp, blue), Ultrabithorax (Ubx, cyan), Abdominal-A (AbdA, green) and Abdominal-B (AbdB, yellow) are shown. Anterior is to the top in panels A-E. (B-E) Single confocal sections of the thoracic (above dotted line) and abdominal (below dotted line) regions of the CNS isolated from 78-hour larvae. (B,C) H3p/AbdA labelling of balanced control (B) and grh³⁷⁰ hemizygous (C) larvae showing that loss-of-grh activity reduces the mitotic index in the thorax but leads to ectopic mitoses in the abdomen. (D,E) 72-78-hour BrdU-pulse labelling of wild-type control (D) and grh³⁷⁰ hemizygous (E) larvae showing that removing neural grh function leads to fewer thoracic cells progressing through S-phase but that numerous ectopic S-phases occur in the abdomen. (F) Histogram showing the total thoracic number of Miranda-positive cells at 72 hours (Mira⁺ neuroblasts), or lineages incorporating BrdU from 72-78 hours (BrdU⁺ lineages). In both cases, a reduction (star indicates significance at P=0.002) is observed in grh³⁷⁰ hemizygotes (for Mira: n=9 larvae, mean=114.6, s.d.=8.6; for BrdU: n=7, mean=100.7, s.d.=18) relative to balanced siblings (for Mira: n=9, mean=138.1, s.d.=16.8; for BrdU: n=6, mean=140.1, s.d.=16.9). (G) Histogram showing that the number of cells per thoracic lineage incorporating BrdU during the 72- to 78-hour window is higher for wild-type control larvae (n=52 lineages, mean=7.1, s.d.=2.1) than for grh³⁷⁰ hemizygotes (n=57, mean=5.3, s.d.=2.4).

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