Fig. 2

Slow-fibre differentiation requires the repressive function of Prdm1. (A) Prox1 expression in slow-muscle fibres of wild-type (wt) embryos at 24 h. (B) ubo^tp39 mutant embryos lack Prox1-expressing slow fibres at 24 h. (C) Eng–Prdm1 expression, marked by tdTomato (tdTOM), rescues mononucleate fibre differentiation and Prox1 expression in ubo^tp39 homozygotes (49 out of 94 Eng–Prdm1-expressing fibres were Prox1 positive; n=8). (D) VP16–Prdm1 expression, marked by tdTOM, was found exclusively in multinucleate fibres lacking Prox1 staining in ubo^tp39 homozygotes (none of the 134 Vp16–Prdm1-expressing fibres was Prox1 positive; n=11). (E) Precocious labelling with the fast-specific F310 antibody in VP16–Prdm1-expressing muscle precursors at the 12-somite stage (12s; 12 out of 30 F310-positive cells; n=4). Scale bars, 25 μm. Eng, Engrailed; Prox1, prospero-related homeobox gene 1; sib, sibling; ubo, u-boot.