Fig. 3

Fig. 3 Neural crest does not account for superficial somite pax3/7 expression. (A) In situ mRNA hybridisation at 27 hpf for sox10, dlx2a, pax3 and pax7. Upper panels show lateral views, dorsal to left anterior to top, lines indicate locations of cryosections in lower panels. Note the punctate distribution of sox10 expression (arrows) on lateral pathway only in anterior sections compared with uniform distribution of pax3/7 mRNA at all axial levels (arrowheads). (B) Electron micrograph of longitudinal section of 24 hpf somite revealing rounded cells (blue) overlying flattened external cells (red) superficial to myofibril-containing slow fibres (SSF). ep, epidermis. Scale bar = 10 μm. (C) In situ hybridisation of 27 hpf embryos reveal the increase of col1α2 as pax7 declines (arrowheads). (D) Lateral view, dorsal to top anterior to left of confocal stacks of superficial region of wholemount immunodetection for Pax3/7 (red, upper panels) or Pax7 (red, lower panels) and myosin (MF20, green) of 24 hpf sibling (left) and colourless (right) embryos. Note the strong Pax-expressing cells (putative neural crest cells, arrows) are missing in cls, whereas the abundant weak Pax-expressing cells are still present (arrowheads). Insets show Pax channel alone at superficial (upper insets) or deep (lower inset) level within the somite. (E) Lateral views of wholemount in situ mRNA hybridisation for pax3 and pax7 in smoothened mutants and control siblings at 24 hpf. Note the persistence of abundant mRNA in the somitic region as somites mature in the absence of slow muscle (arrowheads).