Figure 2.

Effect of GRP94 deletion on production of muscle IGF. A) IGF-I contents of extracts of tibialis anterior and gastrocnemius muscles from the indicated ages, and genders were determined by ELISA. □, WT mice; ●, mGRP94^−/− mice. Each point represents an individual mouse. The 4-wk-old cohort consisted of 8 males and 5 females. B) Skeletal muscle IGF-I level correlates with the level of GRP94 protein. The values of tissue IGF-I from individual 8-wk mGRP94^−/− females (●) and mGRP94^+/− females (▲) were plotted as a function of the amount of GRP94 protein from the same samples, estimated by Western blots of the harvested TA or gastrocnemius muscles. The nondepleted samples were from WT littermates (□). C) Quantitation of IGF-I secreted by primary myoblasts. Cultures were set up in triplicate as described in Materials and Methods, supernatants were collected at the indicated time points, and their IGF-I contents were measured by ELISA. Shown is a representative experiment out of two independent repetitions, with cultures from 3 mice per genotype. *P < 0.05 vs. corresponding WT; unpaired t test. D) Quantitation of IGF-II secreted by primary myoblasts (as in C).