Fig. 2

Mef2ca is up-regulated by muscle activity and essential for muscle growth.

(A–C) MS222 preferentially suppresses the level of Mef2c protein. Zebrafish embryos were incubated from 31–48 hpf with MS222 and Mef2 and MyoD (A, B) or specifically Mef2c (C) were detected by Western blot (50 embryos/sample). Whereas Mef2 decreased, Myod and Vinculin were unchanged relative to Actin control (B). (D–H) Fibers in the midbody region of wild-type embryos (D) or from a mef2ca^tn213/+ incross (E, F) exposed to MS222 or vehicle for 17 h were immunostained for Mef2c (green) and Hoechst (D) and slow MyHC (E, G) or all MyHC (F, H). Mef2c staining identified mutants at the expected frequency. Myofibril bundle width was determined from at least four fibers in somite 17 of nine embryos in each condition (as shown by white arrows in G). Somite volume was calculated by multiplying the length of the somite 17 by the cross-section area (as shown in red in H, n = 17 embryos). Scale bars = 50 μm. Bars represent SEM and samples were compared by t test. All experiments were repeated at least twice.