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Late hyperactivation of Wnt/β-catenin pathway leads to aberrant myofibrillogenesis. (A) axin/apc1 embryos at 36 hpf have thickened slow muscle fibers, left panels. The fast muscle fibers at 36 hpf are detached from the vertical myoseptum, forming lesions (white arrow heads) and are disorganized, middle panels. At 54 hpf, fast muscle fibers are thickened (hypertrophic), right panels. All embryos were imaged at the positions as depicted in cartoons. Images for F59 and Eb165 at 36 hpf are cumulative z-stacks. Images for Phalloidin at 54 hpf are single z-plane at the level of fast muscle fibers. Scale bar, 25 μm. (B) Quantitative real-time PCR (qRT-PCR) of myhz2 (fast muscle specific) and myhz5 (slow muscle specific) mRNA expression normalized to actin. Graphs show that the quantity of myhz5 is not significantly different in axin1/apc1 embryos, failing to identify subtle difference as shown in Fig. 2A. The quantity of myhz2 is upregulated in axin1/apc1 embryos at 54 hpf. (C) LiCl treatment during various time intervals. Early treatment = tailbud stage and 16 hpf for 40 minutes each on the same clutch of embryos, mid treatment = at 16 hpf and 24 hpf and late treatment = at 24 hpf and 30 hpf. Embryos were stained with Phalloidin for visualization of all muscle fibers. All embryos were imaged at the level of the yolk extension, as depicted in cartoon. Images are cumulative z-stacks. Scale bar, 25 μm.
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