Gait alterations in ERR2/3^cko mice.

(A-C) Polygon graphs based on partial least squares (PLS) analysis of 58 gait variables measured during treadmill locomotion at 10 m•s−1 (A), 20 m•s−1 (B), and 35 m•s−1 (C). Optimized model prediction was used to assign data sets for fore and hind limbs to either genotype (control versus ERR2/3cko) and the two components of the models were plotted against each other. Each one of the tested animals is represented by a single dot, while polygons group the animals of the same genotype. The amount of between-groups variance explained by each component in the model is expressed in percent of the total between-groups variance. The two components of our optimized models captured more than 25% of the variance in the predictors in both fore and hind limb at all treadmill speeds. These scores indicate that the method was able to capture the maximum variance between genotypes in the first dimension, which is also shown by the absence of overlap between the two groups on the x-axis, together indicating that ERR2/3cko exhibit significant gait alterations compared to control mice. Yet, all ERR2/3cko mice analyzed were able to successfully complete the treadmill locomotion tasks at all speeds tested (provided as the number of animals “n” running until “completion” for each speed). (D, E) Ranking of the variables’ predictive capacities in the forelimb (D) and hind limb (E) models. The most predictive parameters display the highest loadings (arbitrary units) independent of their sign. The mean value of all mice from the same group was calculated for each parameter and depicted in the bar charts. The sign of the loadings only indicates the direction in which gait parameters are affected (increased, red, or reduced, blue, in ERR2/3cko compared to control mice). (F-I) Examples of Ia afferent recordings from extensor digitorum longus (EDL) nerve-muscle preparations. Red traces: Ia afferent firing, blue traces: relative muscle length, green traces: relative muscle tension upon application of muscle stretch with a force transducer. (F, G) In the control preparation, Ia afferents exhibit relatively low tonic firing rates at resting length, which rapidly increases upon application of muscle stretch with two characteristic bursts during stretch onset and offset. (H, I) In Err2/3cko mice, Ia afferents frequently fall silent during resting length, while exhibiting a responsiveness towards stretch similar to control Ia afferents. Data for S10A-S10E Fig can be found in S3 Data. (TIF)