miRNAs halt cell cycle

Muscle-specific miRNAs can induce differentiation at least in part by depleting DNA polymerase α mRNA, according to Kim et al. (page 677). Although other factors are also involved in the differentiation process, obliterating the DNA replication machinery is a novel means to bring the cell cycle to a halt in differentiating cells.

Kim et al. started with the miR-1, -133, and -206 miRNAs because they are known to be expressed in muscle and heart. Expression of all three increased when C2C12 myoblast precursors were induced to differentiate into muscle by the withdrawal of serum. In fact, expression of miR-206 was sufficient to induce differentiation even in serum. Conversely, blocking its expression dramatically reduced the fraction of cells that exited the cell cycle and differentiated.

To identify targets of these miRNAs, the researchers looked at...