Flow to the front

Cortical actomyosin flow carries polarity proteins to the front of the worm embryo, according to Edwin Munro (Center for Cell Dynamics, Friday Harbor, WA), Jeremy Nance, and James Priess (Fred Hutchinson Cancer Research Center, Seattle, WA). Similar flows may set up polarity in many other systems.

The idea that asymmetrical contraction drives cortical flow and the segregation of cell fate determinants has a long and controversial history. Earlier efforts were dogged by the transience of the flow and different results after the use of different fixation methods.

But when Munro finally had GFP-labeled myosin to work with, “the whole story unfolded in front of me,” he says. Contractile, coupled foci of cortical myosin gave way at the posterior when the sperm centrosomes approached the posterior cortex. The actomyosin network then contracted toward the anterior,...