Fig. 8

ESCO2 depletion in zebrafish is associated with an increase in phospho-H3 staining, and L-leucine partially rescues the increase.

(A). Embryos (1–2 cells) were injected with ESCO2-5mis or ESCO2-MO (4 ng), and immediately separated for D-Leu or L-Leu incubation (10 mM). At 24 h.p.f., cells were immunostained with anti-phospho-Histone H3 (pH3) antibody to detect mitotic cells. Scale bar = 200 μm. (B). The number of cells in mitosis was quantified for 5 embryos per group. P<0.0001, ESCO2-MO with D-Leu treatment vs ESCO2-5mis with D-Leu treatment; P<0.0001, ESCO2-MO with D-Leu treatment vs ESCO2-MO with L-Leu treatment. (C). A working model for the pathways involved in RBS is presented. Due to mutation in ESCO2, significant intracellular stress occurs due to defects in DNA replication, repair, and rDNA processes. This stress is detected by AMPK which can signal the activation of p53 [116] and the phosphorylation of TSC2. The phosphorylation of TSC2 will act to inhibit mTORC1 and downstream effectors such as 4EBP1, S6, and S6 kinase with the ultimate effect being the inhibition of translation. With the addition of L-leucine (green arrows), the leucyl tRNA synthetase will collaborate with the Rag GTPase to activate mTORC1, partially rescuing translation.