Engineered FSHD mutations results in D4Z4 heterochromatin disruption and feedforward DUX4 network activation
Xiangduo Kong,
Nam Viet Nguyen,
Yumeng Li,
Jasmine Shaaban Sakr,
Kate Williams,
Sheila Sharifi,
Jonathan Chau,
Altay Bayrakci,
Seiya Mizuno,
Satoru Takahashi,
Tohru Kiyono,
Rabi Tawil,
Ali Mortazavi,
Kyoko Yokomori
Affiliations
Xiangduo Kong
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Nam Viet Nguyen
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Yumeng Li
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Jasmine Shaaban Sakr
Department of Development and Cell Biology, School of Biological Sciences, University of California, Irvine, Irvine, CA, USA
Kate Williams
Department of Development and Cell Biology, School of Biological Sciences, University of California, Irvine, Irvine, CA, USA
Sheila Sharifi
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Jonathan Chau
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Altay Bayrakci
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA
Seiya Mizuno
Laboratory Animal Resource Center in Transborder Medical Research Center, University of Tsukuba, Tsukuba, Ibaraki, Japan
Satoru Takahashi
Laboratory Animal Resource Center in Transborder Medical Research Center, University of Tsukuba, Tsukuba, Ibaraki, Japan; Department of Anatomy and Embryology, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
Tohru Kiyono
Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, Kashiwa, Chiba, Japan
Rabi Tawil
Neuromuscular Disease Unit, Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA
Ali Mortazavi
Department of Development and Cell Biology, School of Biological Sciences, University of California, Irvine, Irvine, CA, USA; Corresponding author
Kyoko Yokomori
Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA, USA; Corresponding author
Summary: Facioscapulohumeral dystrophy (FSHD) is linked to contraction of D4Z4 repeats on chromosome 4q with SMCHD1 mutations acting as a disease modifier. D4Z4 heterochromatin disruption and abnormal upregulation of the transcription factor DUX4, encoded in the D4Z4 repeat, are the hallmarks of FSHD. However, defining the precise effect of D4Z4 contraction has been difficult because D4Z4 repeats are primate-specific and DUX4 expression is very rare in highly heterogeneous patient myocytes. We generated isogenic mutant cell lines harboring D4Z4 and/or SMCHD1 mutations in a healthy human skeletal myoblast line. We found that the mutations affect D4Z4 heterochromatin differently, and that SMCHD1 mutation or disruption of DNA methylation stabilizes otherwise variegated DUX4 target activation in D4Z4 contraction mutant cells, demonstrating the critical role of modifiers. Our study revealed amplification of the DUX4 signal through downstream targets, H3.X/Y and LEUTX. Our results provide important insights into how rare DUX4 expression leads to FSHD pathogenesis.
