Figure 3.

Mice lacking skeletal muscle ERRα and ERRγ have similar BW, muscle mass and muscle strength as control littermates. A) Body weight (BW) and B) Body composition, determined by EchoMRI, of ERRα/γ dmKO (red bars) and control (gray bars) littermates (n = 12 males/group, 6-month-old). C) Representative images of hind limb muscles of WT and ERRα/γ/dmKO littermates. D,E) Weights of the indicated skeletal muscles, expressed relative to body weight (n = 12/group, 6-month-old). F) Distribution of fiber sizes, measured as minimal Feret's diameter (μm) and expressed as % of total fibers, in EDL and soleus of ERRα/γ dmKO compared to control littermates (n = 3 mice/group, 6-month-old, with at least 1400 individual fibers quantified per muscle and genotype). G) Representative H&E staining of cross sections of EDL and soleus muscles of ERRα/γ dmKO and control littermates (scale bar: 50 μm) (n = 3/group, 6-month-old). H) Percentage of fiber types, quantified in soleus of ERRα/γ dmKO and control littermates by immunofluorescence for type I and type IIa (n = 3/group, 6-month-old); “other” fibers were negative for type I/IIa or their staining was ambiguous and not clearly assigned to type I or IIa. I) Relative mRNA levels of Myh7 (type I MHC) and Myh2 (type IIa MHC) in soleus of ERRα/γ dmKO compared to control littermates (9 WT and 8 KO males, 6-month-old). J) Average fore limb and all-four limb grip strength of ERRα/γ dmKO and control littermates, expressed as force (N, Newtons). Data are from 10-week-old mice (7 WT and 7 KO males; 8 WT and 5 KO females). Data in all panels are the mean ± SEM. ∗, ∗∗, ∗∗∗, p < 0.05, 0.01, 0.001.