Downregulation of Cul4B in NPCs or NT-2 cells led to cell cycle arrest at the G2/M phase. A. Downregulation of Cul4Bs by shRNAs via HSV-1 vector suppressed Cul4B levels in NT-2 cells. The control expressed missense shRNA. n = 3. B. Cul4B shRNA suppressed Cul4B expression in rat NPCs. NPCs transfected with the control vector or the Cul4BshRNA vector were identified by GFP expression. Images were collected in the same settings. Analyses of GFP-positive cells showed that Cul4BshRNA significantly downregulated Cul4B in NPCs (p < 0.04, t-Test). Density of Cul4B fluorescence is presented in the bar graph (Y-axis, arbitrary levels). C. Flow cytometric data analyses show that Cul4B downregulation by shRNAs arrested the cell cycle at the G2/M phase in NPCs. NPCs were transfected or infected with the shRNA vector (control) or the vector that had Cul4BshRNA. The graph represented data analyses from four independent experiments. Control versus shRNA-expressing cells in the G2/M phase, two tail t-Test, p = 0.03. D. A representative histogram of NT-2 cells shows that downregulation of Cul4B by Cul4BshRNA via HSV-1 vector increased the number of cells in the G2/M phase of the cell cycle. A representative experiment is shown. n = 3. No increase in apoptotic cells (sub) was found due to Cul4BshRNA expression in either NT-2 cells or NPCs.