Figure 5. Expression of fast isoforms of myosin heavy chains is reduced in mutant SMAΔ7 muscles.
A–C', Cryostat cross-sections immunostained with myosin heavy chain antibodies to identify fast, slow and embryonic types. P12 sternomastoid (top row) and soleus (bottom row) reacted with 3 of the antibodies used: A, A', antibodies for fast myosin, 10F5 for IIb in A, N1.551 for IIa and neonatal myosin in A'; B, B', A4.840 for slow myosin; C, C', F1.652 for embryonic myosin. Each pair of muscle sections shows the larger, control muscle and the smaller, mutant muscle (left and right in each pair, respectively). D, Fraction of muscle fibers of each type in mutant and control sternomastoid and soleus muscles. In the mutant muscles, fast type fibers are reduced, embryonic-expressing fibers are increased, while slow, type I fibers are unchanged. In each case 3 muscles of each type and age were examined; asterisks indicate statistical significance of comparisons (* p<0.05; ** p <0.01).