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First published online February 4, 2009
doi: 10.1242/10.1242/jcs.038356

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Induced early expression of mrf4 but not myog rescues myogenesis in the myod/myf5 double-morphant zebrafish embryo

Esther Schnapp^1,*, Anna Silvia Pistocchi^2,*, Evangelia Karampetsou², Efrem Foglia², Carla Lora Lamia², Franco Cotelli^2, and Giulio Cossu^1,2,

¹ Stem Cell Research Institute, DiBiT, San Raffaele Scientific Institute, 58 via Olgettina, 20132 Milan, Italy
² Department of Biology, University of Milan, 26 via Celoria, 20133 Milan, Italy

Authors for correspondence (e-mails: franco.cotelli{at}unimi.it; cossu.giulio{at}hsr.it)

Accepted 13 October 2008

Muscle regulatory factors activate myogenesis in all vertebrates, but their role has been studied in great detail only in the mouse embryo, where all but myogenin – Myod, Myf5 and Mrf4 – are sufficient to activate (albeit not completely) skeletal myogenesis. In the zebrafish embryo, myod and myf5 are required for induction of myogenesis because their simultaneous ablation prevents muscle development. Here we show that mrf4 but not myog can fully rescue myogenesis in the myod/myf5 double morphant via a selective and robust activation of myod, in keeping with its chromatin-remodelling function in vitro. Rescue does not happen spontaneously, because the gene, unlike that in the mouse embryo, is expressed only at the onset of muscle differentiation, Moreover, because of the transient nature of morpholino inhibition, we were able to investigate how myogenesis occurs in the absence of a myotome. We report that in the complete absence of a myotome, subsequent myogenesis is abolished, whereas myogenesis does proceed, albeit abnormally, when the morpholino inhibition was not complete. Therefore our data also show that the early myotome is essential for subsequent skeletal muscle differentiation and patterning in the zebrafish.

Key words: Skeletal myogenesis, MRF, Zebrafish, myf5, Myod, mrf4, Myogenin, Myotome

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