Transgenic mice expressing tunable levels of DUX4 develop characteristic facioscapulohumeral muscular dystrophy-like pathophysiology ranging in severity

Takako I. Jones; Guo-Liang Chew; Pamela Barraza-Flores; Spencer Schreier; Monique Ramirez; Ryan D. Wuebbles; Dean J. Burkin; Robert K. Bradley; Peter L. Jones

Similar model-specific effects need to be taken into account when injecting TMX to generate the moderate and severe models, but these are even more pronounced. Importantly, while the moderate model showed consistently different levels of TMX-induced recombination between anatomical muscles ( Figure 1B) , these were different from the leaky recombination in . CC-BY-NC 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/471094 doi: bioRxiv preprint the mild model and more likely a reflection of the difference in TMX accessibility to various muscles. The moderate model mice also showed significant differences between male and females with respect to weight ( Figure S3 ), treadmill profiles (Figure 4) , and muscle physiology ( Figures 5 and S4) , with females being more severely affected by all metrics. With respect to appearance and progression of pathology, the mice show further reduction in Mstn expression, and, as opposed to the mild model, the moderate model mice showDUX4-induced apoptosis ( Figure 12 ) and recruitment of immune cells to the damaged muscle ( Figure 14) . DUX4-FL protein expression, apoptosis, and immune cell recruitment all peak at MD14, at which point there is also an increase in eMyHC positive, newly regenerated fibers as wells as fibrosis (Figures 16 and S8 ). Muscles at this stage produce ~60% of the force produced by ACTA1-MCM controls ( Figure 5 ). Analysis of global differential gene expression supports the activation of apoptosis, the immune response, and the cell cycle, all three of which are much larger groupings than enriched in C2C12 cells expressing DUX4. This illustrates a key difference between performing studies in vitro using single cell types overexpressing DUX4 compared with studies of intact muscle expressing mosaic levels of DUX4 and containing all associated cell types (Figure 7) .