Actin-myosin tears it up

Caspase cleavage of nuclear lamin proteins was thought to be sufficient to cause disintegration of the nucleus during apoptosis. Now, Croft et al. (page 245) show that the actin-myosin cytoskeleton generates a pulling force required to tear apart the structure.When studying the role of actin and myosin in plasma membrane blebbing and cell contraction during apoptosis, the team noticed that if they inhibited ROCK I, a kinase that increases actin contractility and is activated by caspase cleavage, DNA was efficiently fragmented but did not end up in the expected biochemical fractions. The team hypothesized that ROCK I and the actin cytoskeleton might be involved in apoptotic nuclear breakdown.

In the current study, Croft et al. found that after blocking ROCK I activity and thus myosin light chain (MLC) phosphorylation, the nuclear envelope remained intact. Thus,...