Video caption: These mice are siblings and genetically identical. In the one on the right, we turned DUX4 “on”, while in the one on the left, the DUX4 gene remained “off”. FSHD mice have a slow and unsteady gait caused by weakened muscles. You may also notice a hunched back, which is also a sign of muscles being too weak to support the skeleton properly. We are using these animals to test therapies that inhibit DUX4. Credit to Carlee Giesige, a PhD student in the lab, for the video and for characterizing these mice.
by Scott Harper, PhD, Columbus, Ohio
Mouse models of disease are important tools for developing therapies. During the past decade or so, several attempts have been made to generate FSHD mouse models that express the DUX4 gene in their chromosomes.
Although these models were designed logically, the animals were difficult to produce, and they did not show the muscle weakness and damage seen in humans. These first models also suggested that it was difficult to make mice expressing human DUX4, because the gene was toxic and incompatible with normal mouse development.
We concluded that if we wanted to make a DUX4 mouse, we would have to tightly control when and where it could be turned “on,” and began working to generate a new FSHD mouse model in 2009. After many difficulties, we finally successfully produced a model in which DUX4 could be turned on only in muscles.
Our new mice are able to reproduce easily, express DUX4 in muscle, and develop features of muscle disease in the whole animal and microscopically. For example, compared to normal mice, our DUX4 mice have weaker muscles, microscopic evidence of muscle cell damage, are less active, and have an unsteady and slower gait.
We are using these animals to test therapies for FSHD targeting DUX4, and are making them available to any researchers in the FSHD field who think they may be useful. We would like to thank the Muscular Dystrophy Association, FSH Society, and their donors and scientific boards for supporting this work.
Technical summary
These mice contain a CRE-inducible transgene knocked into the ROSA26 locus as a single copy. A FLOXED-Neomycin resistance gene is cloned upstream of a V5 epitope-tagged DUX4. The construct also has the 3’ UTR including the pLAM poly A. We breed the mice to the HSA promoter-CRE-ERT2 line available from Jackson Laboratory.
Double transgenics are viable, have zero DUX4 leakiness, and we get Mendelian ratios. DUX4 can be turned on with Tamoxifen. At high doses of Tamoxifen, animals are non-ambulant by seven days. At low doses, animals show a gait defect, muscle histopathology, TA-specific force deficits, and and significantly reduced activity. (Note: the mouse genes are artificially engineered so that the drug Tamoxifen can be used switch DUX4 on. Normally, Tamoxifen had no effect on DUX4.)
For questions and to request mice, please contact Scott Harper. Phone: (614) 355-2893. Email: scott.harper@nationwidechildrens.org.
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