Fig. 6. Manipulating dpERK levels leads to loss of scleraxis expression and rib defects. (A,D,F) Whole-mount in situ hybridisation of (A,D) scleraxis (dark blue) and (F) scleraxis with GFP (red). (A) hMKP3-GFP electroporation and (D) caMEK1 electroporation resulted in loss of scleraxis transcripts (n=19/22 and n=10/14). (F) GFP electroporation had no effect (n=16/16). (B,C,E,G) Alcian Blue staining of cartilage. Loss of dpERK resulted in loss of the distal part of rib one (B, n=8/12) or rib seven (C, n=9/16), depending on the somites targeted. (E) High levels of dpERK caused loss of the distal part of rib one (n=9/15). (G) GFP alone had no effect on rib development (n=12/12). (H) Infection of thoracic somites with RCAS-sFREK:Fc, at day 10 of development, multiple ribs failed to form (n=2/16). (I) In situ hybridisation detecting RCAS gag transcripts 48 hours after infection (red). (J) Transverse section through RCAS infected somite demonstrates presence of transcripts predominantly in the dorsal somite. Asterisks indicate missing ribs (B,C,E,H) compared with rib present in control (G). dm, dermomyotome; my, myotome; sc, sclerotome.