Cell‐cycle regulation of sarcomere integrity—Role for Actn2 phosphorylation

, that matches the consensus phosphorylation motif of the cell-cycle kinase CDK1. In vitro kinase assays showed that CDK1 phosphorylates Actn2 at T308. In contrast, CDK1 was unable to phosphorylate Actn2 when T308 was mutated to alanine (T308A). Using CRISPR-Cas9 gene editing, we created Actn2-T308A and phosphomimetic Actn2-T308D variants in C2C12 cells. C2C12 cells expressing Actn2-T308A differentiated rapidly and formed robust sarcomeres. However, C2C12 cells expressing Actn2-T308D failed to form organized sarcomeres. Curiously, Actn2-T308A cells were found to have less proliferative capacity than Actn2-T308D cells. Taken together, these results identify CDK1-dependent phosphorylation of Actn2-T308 as being important for sarcomere assembly. Moreover, the data also suggest a mechanism by which cell-cycle exit promotes sarcomere assembly.