Fig. 8

Fig. 8 The prdm1:gfp transgenic reporter provides a lineage tracer to follow the fate of prdm1-dependent muscle precursors in ubo (prdm1) mutants. (A) Transverse sections show colocalisation prdm1:gfp with smyhc1-CDS in situ hybridisation in ubo (prdm1)^tp39 mutants and wild-type siblings at 24 hpf. At 48 hpf, the prdm1:gfp marked muscle fibres are still present in ubo (prdm1)^tp39 mutants, although Smyhc expression is reduced. Cell boundaries are marked with anti-β-catenin 15B8. (B) Lateral views showing that muscle fibres with prdm1:gfp form a superficial layer of horizontal, mononucleate fibres in 48 hpf wild-type embryos but are among the fast fibres in ubo (prdm1)^tp39 mutants and like fast fibres are frequently multinucleate (TOTO stain) and orientated diagonally. (C) Transverse sections at 48 hpf show colocalisation of F310 fast muscle antigen with prdm1:gfp in ubo (prdm1)^tp39 mutants but not in wild-type siblings. (D) In posterior trunk at 48 hpf, in ubo (prdm1)^tp39 mutants, the dorsal fibres with persistent slow MyHC S58 antigen are marked with prdm1:gfp and fast muscle F310 antigen. (E) In posterior trunk at 36 hpf, in ubo (prdm1)^tp39 mutants, even the most dorsally positioned fibres marked with prdm1:gfp lack Prox1 (arrows). Note the intense Prox1 staining in isolated cells external to the myotome (arrowheads). (F) In posterior trunk of cyclopamine-treated embryos, prdm1:gfp marked secondary fibres colocalise with slow MyHC S58 antigen but not fast muscle F310 antigen in genotyped wild-type siblings and vice versa in genotyped ubo (prdm1)^tp39 mutants. Scale bars: 25 μm.