Tugging and pulling in asymmetric cell divisions

In asymmetric divisions, the cell alters the normal process that centers the spindle in the mother cell, but how it regulates the timing of spindle movement is unclear. Now, on page 245, Labbé et al. describe a tethering system that resists premature movement of the mitotic spindle during asymmetric cell divisions in C. elegans embryogenesis.

It was known that when researchers cut spindle microtubules with a laser, both centrosomes moved toward their respective cell poles, but the posterior one moved more quickly. To find out what establishes these uneven pulling forces and when the asymmetry first arises, Labbé and his colleagues used a laser to sever microtubules at different times throughout the first cell cycle. If they destroyed the anterior centrosome in prophase, the posterior centrosome moved posteriorly. But after destruction of the...