June 5 @ 11:00 AM – 12:00 PM
Dr. Kyoko Yokomori
Professor, SOM – Biological Chemistry
University of California, Irvine
“CRISPR-Engineered mutations and MERFISH single cell spatial transcriptomics reveal key processes of FSHD pathogenesis”
Abstract: Facioscapulohumeral dystrophy (FSHD) is a third common muscular dystrophy and is linked to contraction of D4Z4 macrosatellite repeats on chromosome 4q with SMCHD1 mutations acting as a disease modifier. D4Z4 repeats form heterochromatin (DNA methylation and histone H3K9me3), and its disruption and abnormal derepression 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 protein expression was found only in <1% of patient myocytes. We generated isogenic mutant cell lines harboring D4Z4 and/or SMCHD1 mutations in a healthy human skeletal myoblast line using CRISPR-Cas9. We found that the two 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 epigenetic modifiers. We also found amplification of the DUX4 signal through coherent feed-forward mechanism by downstream targets, such as histone H3 variants, H3.X/Y, and the LEUTX transcription factor. MERFISH-based gene network profiling of multinucleated cells identified FSHD-induced transcriptomic alterations during myoblast differentiation into myotubes. Patient and mutant myotubes are found in “FSHD-hi” and “FSHD-lo” states with the former signified by high DUX4 target expression and decreased muscle gene expression. Importantly, both states are distinct from that of control myotubes. Pseudotime analyses reveal a clear bifurcation of myoblast differentiation into control and FSHD-hi myotube branches with varying numbers of DUX4 target-expressing nuclei. We found that not all DUX4 target genes are expressed equally and that LEUTX represents a sub-pathway within the DUX4 gene network globally increasing DUX4 target gene expression as well as interfering with proper regulations of mitotic and muscle genes during myotube differentiation. Taken together, our results indicate that heterochromatin loss enables limited expression of DUX4 at D4Z4, and that its signal is further amplified by downstream target transcription/chromatin factors differentially contributing to the disease transcriptomic phenotype.
This work was supported in part by a grant R01AR071287 from National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Host: Elnaz Abdollahzadeh
Seminar will be held in person only.
For questions about this event, please contact Mayra Rubio at mrubio3@uci.edu.