Identification of SMCHD1 domains for nuclear localization, homo-dimerization, and protein cleavage.

SMCHD1 is a disease modifier and a causative gene for facioscapulohumeral muscular dystrophy (FSHD) type 1 and type 2, respectively. A large variety of different mutations in SMCHD1 have been identified as causing FSHD2. In many cases, it is unclear how these mutations disrupt the normal function of SMCHD1. We made and analyzed lenti-viral vectors that express Flag-tagged full-length or different mutant SMCHD1 proteins to better understand the functional domains of SMCHD1 in muscle cells. We identified regions necessary for nuclear localization, dimerization, and cleavage sites. Moreover, we confirmed that some mutants increased DUX4 expression in FSHD1 myoblasts. These findings provide an additional basis for understanding the molecular consequences of SMCHD1 mutations.