Expression of myh7 myofibers of zebrafish EOMs. (A–D) Ventral view of the zebrafish EOMs (dashed squares) in double transgenic lines, Tg(mylz2:GFP, green, identifies all fast myofibers) and Tg(smyhc:tdTomato, red, identifies all slow myofibers) of obscna+/−;obscnb+/− and obscna−/−;obscnb−/− zebrafish larvae at 5 dpf. C and D show the EOMs in the marked areas in A and B at higher magnification. (E) Measurement of fast (identified by Tg(mylz2:GFP) and slow Tg(smyhc:tdTomato) myofibers total size (µm) in the EOMs relative to controls measured in midportion of the EOMs, indicated by white line in C, presented in percentage. (F–H) Ventral view of wild-type zebrafish larvae at 5dpf showing expression of cardiac myosin heavy chain genes, (F) myosin heavy chain 7bb (myh7bb), (G) myosin heavy chain 7-like(myh7l), and (H) myosin heavy chain 7 (myh7) probes in the EOMs and the cardiac muscle, arrowheads indicate EOMs, MM = masticatory muscle and CM = cardiac muscle. The qPCR showed the mRNA level of (I) myh7bb, (J) myh7l, and (K) myh7 in obscna−/−;obscnb−/− and obscna+/−;obscnb+/− zebrafish larvae. Expression of myh7 was significantly increased in EOMs. (L–O) EOMs from obscna+/−;obscnb+/− treated with myh7 antisense probe showing small subgroup of myh7-positive myofibers (L, N, arrowheads), never overlapping with S58 labeled slow myofibers (M, O, open arrowheads) and (P–S) EOMs from obscna−/−;obscnb−/− where open arrowheads indicate myh7-positive myofibers. The areas indicated by the squares in L, M, P, and Q are shown below in higher magnification. (T) Quantification of the number of myh7 positive myofibers in obscna−/−;obscnb−/− (n = 9) and obscna+/−;obscnb+/− (n = 11). *P < 0.05; ****P < 0.0001.
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