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

Two dosing regimens of TMX were tested in the ACTA1-MCM;R26 NZG bi-transgenic offspring, a single low dose (5mg/kg) intraperitoneal (IP) injection and two IP injections on consecutive days of a higher dose (10mg/kg). Expression of the nLacZ reporter gene was visualized by X-Gal staining [67] in the gastrocnemius muscles isolated two weeks after TMX injection. The results indicated that both dosing regimens produced mosaic patterns of Cre-mediated recombination in skeletal muscle, with the high TMX dose producing ~1.5X more X-Gal stained nuclei than the low dose ( Figures S1 and S2) . Surprisingly, in the absence of TMX the ACTA1-MCM;R26 NZG mice also showed transgene recombination, although only in a very small fraction of skeletal muscle nuclei ( Figure S1C ). Interestingly, this low-level recombination and nLacZ expression was not uniform across all nuclei; rather, it also showed a mosaic pattern of recombination (~one-third the number of recombined nuclei induced by the low TMX dose, Figure S2C The copyright holder for this preprint (which was not peer-reviewed) is the author/funder.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 differing levels of mosaic transgene recombination. Genomic DNA was isolated 3 days postinjection (DPI) of TMX and assayed for transgene recombination by genomic PCR ( Figure 1B ).