Rheb and TOR regulate ribosome biogenesis. (A, B) Nucleoli visualized by anti-fibrillarin staining (green) , in S2 cells treated with (A) DMSO or (B) rapamycin for 16h. DNA was visualized using Hoechst 33258 (blue). (C) Northern blots of RNA from S2 cells treated for 72h with the indicated dsRNA. A probe for an internal transcribed spacer (ITS) region of the rDNA was used to detect pre-rRNA. Total rRNA was detected with ethidium bromide. A probe for dMyc transcript was used as a loading control. (D) Quantification, using ImageJ software, of pre-rRNA and total rRNA, relative to dMyc mRNA, from the samples shown in (C).