Disruption of fiber type identity in adult
mutant fish. (A,B) at 3 months, expression of the tnnc1b:eGFP reporter is restricted to the medio-lateral wedge of slow-twitch fibers in wild-type fish. (C,D) In sox6 mutants, the reporter gene is also expressed at lower levels in fast-twitch fibers while the slow-twitch fibers extend closer to the midline. The diameter of the slow-twitch fibers is significantly reduced compared to wild-type (cf. B and D). (E) The smyhc1:GFP reporter is expressed at high levels in the slow-twitch fiber of 2-month-old fish. (F) the reporter shows a similar pattern of expression in sox6 mutants at the same stage, with lower level expression extending more medially than in wild type.