Fig. 6. dRheb is required in the whole organism for viability and growth. The lethal phase of dRheb^AV4 homozygous mutants was determined by counting dRheb^-/- (identified by lack of GFP expression) and dRheb^+/- (identified by GFP expression) sibs at various times after 2 hour egg collections [A; after egg lay (AEL)]. The dRheb^-/- larvae grow more slowly, as shown by comparison with wild-type at 72 hours AEL (B,C; same magnification). Comparison of mouth hooks shows that wild-type larvae (B) have progressed to second instar, whereas dRheb^-/- larvae (C) remain in first instar.