Table III.
Fiber Type Frequency (%) Is Unaffected by Myogenin Overexpression
| Genotype | n | Proportion of fibers of type | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2A | 2B | 2X* | |||||||
| EDL | ||||||||||
| Wild-type | 4 | 0.9 ± 0.5 | 12 ± 2 | 68 ± 4 | 19 | |||||
| MMg | 4 | 0.7 ± 0.5 | 9 ± 3 | 74 ± 5 | 16 | |||||
| MMg + MId | 3 | 1.2 ± 0.6 | 14 ± 4 | 67 ± 7 | 18 | |||||
| Tibialis anterior (deep) | ||||||||||
| Wild-type | 4 | 2 ± 1 | 24 ± 8 | 47 ± 21 | 27 | |||||
| MMg | 3 | 1 ± 1 | 19 ± 8 | 59 ± 18 | 21 | |||||
| Tibialis anterior (superficial) | ||||||||||
| Wild-type | 4 | 0 | 0 | 91 ± 7 | 9 | |||||
| MMg | 3 | 0 | 0 | 90 ± 3 | 10 | |||||
| Soleus | ||||||||||
| Wild-type | 7 | 55 ± 6 | 51 ± 3 | 0 | 0 | |||||
| MMg | 3 | 60 ± 1 | 41 ± 4 | 0 | 0 | |||||
| MMg + MId | 4 | 57 ± 6 | 49 ± 5 | 0 | 0 | |||||
Serial cryostat sections of muscles from MMg, MMg + MId, and control wild-type littermates were stained with A4.840 (slow, 1), A4.74 (2A), and BF-F3 (2B). Fiber numbers (± SEM) in whole cross sections were counted and scored as positive or negative for each antibody.
2X fiber frequencies are calculated assuming type 1 + 2A + 2B + 2X = 100%, and are shown for comparison. In soleus, a few fibers express both slow and 2A MyHC. MId mice were not analyzed because the small size of fibers in the animals made accurate counting difficult. Most detailed analysis was performed on EDL and soleus in which all fibers in the muscles were scored. For other muscles, a representative field containing ∼250–300 fibers was scored with each antibody in a similar area at approximately the same proximo-distal level within the leg, as judged by independent anatomical markers.