Deletion of a 42 kb super-enhancer at the fast Myosin locus by CRISPR/Cas9 prevented expression of adult fast Myosin genes and resulted in neonatal lethality in mice.
A 42 kb super-enhancer acts as a locus control region that dictates skeletal muscle fiber phenotype by dynamically interacting with and activating specific fast Myosin gene promoters.
The contractile properties of adult myofibers are shaped by their Myosin heavy chain isoform content. Here, we identify by snATAC-seq a 42 kb super-enhancer at the locus regrouping the fast Myosin genes. By 4C-seq we show that active fast Myosin promoters interact with this super-enhancer by DNA looping, leading to the activation of a single promoter per nucleus. A rainbow mouse transgenic model of the locus including the super-enhancer recapitulates the endogenous spatio-temporal expression of adult fast Myosin genes. In situ deletion of the super-enhancer by CRISPR/Cas9 editing demonstrates its major role in the control of associated fast Myosin genes, and deletion of two fast Myosin genes at the locus reveals an active competition of the promoters for the shared super-enhancer. Last, by disrupting the organization of fast Myosin, we uncover positional heterogeneity within limb skeletal muscles that may underlie selective muscle susceptibility to damage in certain myopathies.
Santos et al. (2022) studied Muscle fiber phenotype. CRISPR/Cas9 deletion of fMyh super-enhancer vs. Wild-type was evaluated on Expression of fast Myosin genes. Deletion of a 42 kb super-enhancer at the fast Myosin locus by CRISPR/Cas9 prevented expression of adult fast Myosin genes and resulted in neonatal lethality in mice.