Post-natal expression of Fst-288 promotes profound skeletal muscle hypertrophy. (A) Injection of the anterior musculature of the mouse hind limb with a viral vector designed to express Fst-288 (rAAV6:Fst-288) increased the expression of Fst in treated TA muscles, and increased muscle mass by >100% (*, P < 0.05 vs. control) within 28 d. (B and C) Muscle hypertrophy was a product of increased muscle fiber size (reported here as representative hematoxylin and eosin–stained cryosections, and as box and whisker plots comprising minimum, lower quartile, median, upper quartile, and maximum values for myofiber diameter). Bar, 100 µm. (D) Increased TA muscle isometric force producing capacity in C57BL/6 mice 4 wk after intramuscular injection of rAAV6:Fst-288 (*, P < 0.05 vs. control). (E) Intravenous administration of rAAV6:Fst-288 to mice facilitates systemic dissemination of the vector, resulting in considerable hypertrophy of muscles throughout the body. (F) Increased TA muscle isometric force producing capacity in C57BL/6 mice 8 wk after intravenous injection of rAAV6:Fst-288 (*, P < 0.05 vs. control). Graphs show data from at least four independent experiments. Error bars indicate ± SEM.