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. Author manuscript; available in PMC: 2010 Feb 25.
Published in final edited form as: Cell Metab. 2008 Feb;7(2):159–172. doi: 10.1016/j.cmet.2007.11.003

Figure 1. Conditional Activation of Akt1 in Skeletal Muscle Induces Reversible Type IIb Muscle Hypertrophy.

Figure 1

(A) Top: schematic of doxycycline (DOX) treatment time course. Bottom: representative gross appearance of control and double-transgenic (DTG) mice after 2 weeks of transgene induction and after 2 weeks of induction followed by 2 weeks of repression. This experiment was initiated in DTG mice at 8 weeks of age.

(B) Top: time course of transgene expression following the addition of DOX (induction) and the subsequent removal of DOX (repression). Representative blots of gastrocnemius muscle are shown. Bottom: time course of gastrocnemius muscle weight changes resulting from transgene induction followed by repression (n = 4–12 in each group). *p < 0.05 versus day 0; #p < 0.05 versus day 14.

(C) Gastrocnemius, soleus, and extensor digitorum longus (EDL) muscle weight in control (Cont) and DTG mice at 2 weeks after Akt1 activation (n = 6 in each group).

(D) Histological analysis of myofiber growth. Top: hematoxylin and eosin (H&E) staining of gastrocnemius muscle sections. Scale bar = 100 μm. Bottom left: distribution of mean cross-sectional areas (CSAs) of muscle fibers. Bottom right: mean CSA of muscle fibers (n = 6 in each group).

(E) Top: western blot analysis of transgene expression after 2 and 6 weeks of DOX treatment. Bottom: gastrocnemius muscle weight at 2, 3, 4, and 6 weeks after DOX treatment (n = 6–12 in each group).

(F) Left: representative images of gastrocnemius muscle sections stained with MHC type I, IIa, or IIb antibody (green) and laminin (red) from control and DTG mice 2 weeks after Akt1 activation. Right: distribution of mean CSAs of type IIb muscle fibers from control and DTG mice after 2 weeks of DOX treatment.

(G) Forelimb grip strength of control mice and DTG mice after 2 weeks of DOX treatment (n = 6 in each group).

(H) Results of forced treadmill exercise test on MCK-rtTA single-TG control mice and DTG mice after 2 weeks of DOX treatment (n = 4 in each group). Results are presented as mean ± SEM. *p < 0.05 versus control; N.S., not significant.