An actin-binding protein helps shape the mitotic spindle, Chan et al. report.
Researchers long thought that actin and microtubules performed different tasks during mitosis. They believed that microtubules formed the mitotic spindle that pulls chromosomes apart, whereas actin joined with myosin to produce the contractile furrow that separates the mother and daughter cells. But recent studies have revealed that the roles of the two cytoskeletons converge. For instance, actin helps situate the mitotic spindle, and microtubules help localize the cleavage furrow.
Chan et al. discovered a surprising new example of this functional overlap when they tracked the protein adducin-1. During most of the cell cycle, adducin-1’s C-terminal tail domain fastens onto actin at the cell membrane and helps brace the cortical cytoskeleton and cell–cell junctions. But Chan et al. found that during mitosis adducin-1 attaches to the spindle with its N-terminal head domain.
Adducin-1 relocates to the mitotic spindle when CDK1 phosphorylates two serines in the protein. However, it doesn’t hitch to the spindle directly. Adducin-1 couples to the microtubule-binding motor myosin-X. Chan et al. determined that this connection was crucial for the formation of the mitotic spindle. In cells lacking adducin-1, the spindles were distorted and often displayed multiple poles. How adducin-1 shapes the spindle—and whether actin is involved in that process—remains unclear.
Text by Mitch Leslie