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

A key component of the moderate model is that after MD14 both male and female mice recover on their own, regaining ~50% treadmill running by MD28, which coincides with decreases in apoptosis, eMyHC staining, and immune cell infiltration, although fibrosis remains. This is likely because DUX4-FL positive myofibers die and are being repaired and replaced using satellite cells that did not undergo transgene recombination, and thus have not activated DUX4 expression. Therefore, it is imperative to have the proper controls when using these models for preclinical testing of therapeutics. However, this also presents an opportunity whereby the mice can be re-injected with TMX at some point during treatment and progressive decline of the model can be assessed over several months. Preliminary experiments in our lab suggest that this is a viable possibility that needs further investigation and characterization. In addition, TMX can be adjusted to single higher-dose injections or multiple lower-dose injections to refine the model to meet investigational needs. The flexibility and tunability of this model is almost endless. The copyright holder for this preprint (which was not peer-reviewed) is the author/funder.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 While the moderate model can be assayed over the course of a month, the severe model is only useful for short-term analyses, as the DUX4-induced pathology is so severe that the mice require sacrifice no later than SD10. These mice do not show any signs of recovery. As in the moderate model, there are consistently different levels of transgene recombination and DUX4-fl expression among different anatomical muscles ( Figure 1B) . However, different muscles show the same patterns as in the moderate model (e.g., soleus is highest and quadriceps is lowest for both models), supporting the idea that accessibility to the TMX that is responsible for the variability. In addition, as seen for both the mild and moderate models, females and males of the severe model showed sex-specific differences, with females again being more severely affected.