Knockout of MYOM1 in human cardiomyocytes leads to myocardial atrophy via impairing calcium homeostasis

Myomesin‐1 (encoded by MYOM1 gene) is expressed in almost all cross‐striated muscles, whose family (together with myomesin‐2 and myomesin‐3) helps to cross‐link adjacent myosin to form the M‐line in myofibrils. However, little is known about its biological function, causal relationship and mechanisms underlying the MYOM1‐related myopathies (especially in the heart). Regrettably, there is no MYMO1 knockout model for its study so far. A better and further understanding of MYOM1 biology is urgently needed. Here, we used CRISPR/Cas9 gene‐editing technology to establish an MYOM1 knockout human embryonic stem cell line (MYOM1(−/−) hESC), which was then differentiated into myomesin‐1 deficient cardiomyocytes (MYOM1(−/−) hESC‐CMs) in vitro. We found that myomesin‐1 plays an important role in sarcomere assembly, contractility regulation and cardiomyocytes development. Moreover, myomesin‐1‐deficient hESC‐CMs can recapitulate myocardial atrophy phenotype in vitro. Based on this model, not only the biological function of MYOM1, but also the aetiology, pathogenesis, and potential treatments of myocardial atrophy caused by myomesin‐1 deficiency can be studied.