Figure 5

Shh/RCAS-infection of chick wings blocks early muscle differentiation. A. Pellet of chick embryo fibroblasts expressing theShh/RCAS replication-competent retroviral vector is grafted into the dorsal mesenchyme of chick right wing buds at HH22 and embryos were maintained to HH27-28. B-G. Contralateral (B-D) and Shh/RCAS infected (E-G) wings were serially sectioned and stained for pan-MyHC (B,E), anti-slow MyHC (C,F), and anti-Hh (D,G) antibodies. Control left wings have a normal distribution of muscle fibres and lack Shh staining in muscle-forming mesenchyme (B-D) whereas some Shh/RCAS right wings show a loss of pan-MyHC-reactive cells (E). Ectopic slow MyHC is present in the anterior dorsal muscle mass (F, arrow). H-J. Fibre numbers counted in adjacent sections at comparable levels of control contralateral and operated HH27-28 limbs. The values presented must be regarded as an imprecise reflection of absolute fibre numbers because resolution of small fibres from adjacent larger fibres was difficult and varied depending on the orientation of fibres within the section. Total fibre numbers (H), slow fibre numbers (I) and the proportion of fibres that contained slow MyHC (J) are presented from four limbs showing normal DMM extent (Increased slow limbs), five limbs showing reduced DMM (Reduced muscle limbs) and the pooled data (All limbs). Dorsal is up and posterior to the left in panels B-G. (u) ulna, (r) radius. Scale bar = 500 μm.