Figure 2.

Numb/NumbL‐specific knockdown in skeletal muscle leads to drastic decrease in contractile muscle force. HSA‐MCM Numb^fl/fl/NumbL^fl/fl mice were treated with vehicle or tamoxifen and sacrificed 56 days post‐induction. (A) Western blot analysis showing reduced levels of Numb protein in tibialis anterior (TA), soleus (Sol), and gastrocnemius (GS) muscles (N = 6 per group). (B) Quantitation of blots shown in (A). Numb levels were normalized to GAPDH (loading control) and expressed relative to the mean level of Numb in vehicle‐treated samples (N = 6 per group). (C–E) Normalized muscle weights; wet muscle weight at time of euthanasia was normalized to pre‐induction body weight (N = 15 per group). (F–I) Force–frequency (F) and specific force–frequency (G) relationships during in situ physiological testing of the gastrocnemius muscle; (H) peak twitch force (Pt); (I) tetanic force (Po); N = 15 for vehicle and 13 for tamoxifen‐treated mice. Statistical analysis was performed with repeated measure one‐way analysis of variance with post hoc Tukey honestly significant difference test (F–G) (force–frequency, F = 4.753, DFn 10, DFd 260, drug × frequency interaction P < 0.0001; specific tension force–frequency, F = 2.150, DFn 10, DFd260, drug × frequency interaction P = 0.0213) or two‐tailed unpaired t‐tests (all other panels). ****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05.