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Fig. 5 Distinct roles for the PI3K-Akt and Mek1/2-Erk1/2 signaling pathways in normal and catch-up growth. (A) Wild-type zebrafish embryos were raised following the experimental regime depicted in Fig. 1A. Embryos in the Norm group were treated with or without LY294002 (5 μM) or U0126 (10 μM) from 26 to 38 hpf. Embryos in the Reoxy group were treated from 36 to 48 hpf. Embryos were sampled in the middle of the experiment (4 hours post drug treatment) and the lysates were assayed for Erk1/2, Akt, S6 and Tubulin by immunoblotting. (B) Effect of LY294002 on normal and catch-up growth. Embryos were treated with LY294002 for 12 hours at the indicated doses. Data are mean ± s.e.m., n=3; *, P<0.05 compared with the no treatment control group. (C) Effect of U0126 on normal and catch-up growth. Embryos were treated with U0126 for 12 hours at the indicated doses. Data are mean ± s.e.m., n=3; *, P<0.05 compared with the control group; †, P<0.05 compared with the corresponding Norm group. (D) Forced expression of constitutively active Ras or Akt increases catch-up growth but has no effect on normal growth. Embryos injected with GFP, HA-RasV12 or myr-Akt mRNA (50 pg/embryo) were raised under normoxia or hypoxia until 36 hpf and the HTA determined. Data are mean + s.e.m., n=16-30. Different letters represent significant differences at P<0.05.