(A–C) Knockdown of stg/cdc25 and overexpression of dacapo (dap) in cortex glia prevents cell division. Maximal projection of a VNC for control (A), stg knockdown (B) and dap overexpression (C) conditions. NSC, Deadpan, grey ; glia nuclei, Repo, magenta. (D) Total counts of glial cells normalised to NSC number show that cortex glial division is highly impaired in stg knockdown and dap overexpression in the cortex glia. p(stg RNAi)=7.8*10−6. p(dacapo)=3.0*10−3. n (control) = 10 VNCs. n (stg RNAi)=10 VNCs. n (dap) = 5 VNCs. (E–G’) Preventing cortex glial division does not impair chamber formation. (E) 3D reconstruction of the thoracic section of one VNC of a control condition, ventral view. (E’) Top and bottom panels, orthogonal and ventral views. (F) 3D reconstruction of one VNC thoracic section when stg is knocked-down in cortex glia, ventral view. (F’) Top and bottom panels, orthogonal and ventral views of a portion. (G) 3D reconstruction of one VNC thoracic section when dap is overexpressed in cortex glia, ventral view. (G’) Top and bottom panels, orthogonal and ventral views of a portion. Cortex glial membrane, Nrv2::GFP, green ; NSC, Dpn, grey ; neurons, ElaV, red. (H–K) Chamber organisation chart. The graph represents the signal intensities from cortex glial membranes (green), NSCs (grey) and neurons (red) plotted against depth for one VNC from H) control, (I) stg RNAi and J) dap overexpression. Depth unit is the slice. (K) Statistical representation of NSC (grey) and neuron (red) Z positions relative to the top layer of the cortex glia (green line). p(NSC stg RNAi)=0.78, p(neuron stg RNAi)=0.10. p(NSC dap)=0.32, p(neuron dap)=0 .39. n (control) = 10 VNCs. n (stg RNAi)=7 VNCs. n (dap) = 5 VNCs L) Ratios between cortex glial membrane signal and NSCs. p (stg RNAi)=0.39. p (dap) = 0.73. n (control) = 10 VNCs. n (stg RNAi)=10 VNCs. n (dap) = 5 VNCs).