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Fig. 5 Mef2 controls a transcriptional module involved in thick filament assembly. In situ hybridisation for mRNAs encoding sarcomeric components in 24-hpf control or mef2d/c MO-injected zebrafish embryos. In each panel, cryosections of wholemount embryos, dorsal up, are to the left and flatmounts, anterior up and dorsal to right, are to the right. (A-D) Embryonic fast myhz1 (B), mylz2 (C, 22s) and smbpc (D) mRNAs are grossly downregulated in morphants. Slow fibre-specific smyhc1 mRNA (A) remains abundant. (E-G) mRNA for thin filament-related genes detected with probes to acta1 (E, 21s) or tnnc (G) are unaltered in morphants, whereas tpma (F) is upregulated. Note the lack of change in nuclear Pax3/7 protein (F, brown). (H) mRNA for the myosin chaperone protein hsp90a is also upregulated.