Fig. 2. Fgf8 is required for fast muscle differentiation in the lateral somite. (A) Cryostat sections at the gut extension level of whole-mount in situ mRNA hybridisation for myosin light chain 2 (mylz2) at 20-22 s in unmanipulated control, Fgf8 MO-treated, ace mutant and SU5402-treated embryos. Red brackets show expansion of the lateral undifferentiated tissue. (B-D) Immunohistochemical detection of fast MyHC (B) or slow MyHC (C,D) on whole mounts at 15 s (C) or cryosections of Fgf8 MO-injected and control embryos at 33 hpf (B,D). Brackets indicate expansion of lateral non-muscle tissue, arrows show weakened fast MyHC.