Figure 2: Satellite cells contribute to myofibres in all muscles.

(a) Schematic showing genetic labelling of satellite cells with GFP at 6 months and harvested at either 12 or 20 months. (b–c) GFP is broadly distributed along the length of myofibres (b and left panel c) and, even in GFP myofibres, few myonuclei (orange arrow right panel c) are centrally located. (d–i,k,m) Representative cross-sections of the EDL, TA, gastrocnemius, plantaris, soleus, diaphragm and EOM of 12- or 20-month-old Pax7^CreERT2/+;Rosa^mTmG/+ mice showing GFP+ myofibres to which satellite cells have contributed. It should be noted that the percentage of satellite cell contribution may be inflated in EOM due to the small size of its myofibres, which may reduce dilution of the GFP signal. Scale bar, 100 μm. (j,l) Adjacent sections in the soleus and diaphragm identifying slow MyHCI+ myofibres. White arrows indicate fast GFP+MyHCI− fibres and orange arrows indicate slow GFP+MyHCI+ fibres. Green graphs show %GFP+ myofibres at 12 months (dark green, n=4 for each muscle) or 20 months (light green, n=6 for each muscle). Orange graphs show %GFP+ MyHCI+ myofibres in the soleus (dark orange, n=4 at 12 months; light orange, n=6 at 20 months) and diaphragm (dark orange, n=3 at 12 months; light orange, n=5 at 20 months). Data are expressed as mean±1 s.e.m. for all graphs. Two-tailed student t-test, *P≤0.05, **P<0.01 ***P<0.001.