Fig. 1

Two-weeks of Akt1 transgene activation induces pronounced type IIb muscle growth in double transgenic (DTG) mice. a Skinned hind limbs of a 24-week-old MckrtTA and DTG mice after 2 weeks of doxycycline treatment to activate myr Akt1 transgene expression. b A significant increase in the mass of gastrocnemius muscle was found in DTG mice at 2 weeks after transgene induction compared to MckrtTA mice. c Cross-section of the indicated gastrocnemius muscles stained with laminin (red). d Akt1-induction in DTG mice selectively increased the mass of gastrocnemius (GSN) muscle. e Average cross-sectional area of each myofiber type from DTG mice and their littermate controls (STG) with 2 weeks of doxycycline water. There were significant increases in CSA of type IIb fast-twitch myofibers but reduced CSA of type I and type IIa myofibers in DTG mice compared to STG controls. f Gastrocnemius muscles from DTG showed increased percentage of type IIb myofibers compared to that from STG mice. ***p < 0.001, *p < 0.05