Polarity feeds back

Polarizing cells must first pick a direction. The external cues that guide this choice are obvious: bud scars or mating partners for budding yeast, and chemoattractant gradients for Dictyostelium and neutrophils. But polarization still occurs, albeit in a random direction, when these cues are either removed or made uniform.Now, Roland Wedlich-Soldner, Rong Li (Harvard Medical School, Boston, MA), and a group of mathematical modelers have come up with an explanation for this intrinsic polarization in budding yeast. In wild-type situations, the intrinsic mechanism may be used to solidify the direction originally dictated by the external cue.

Normally, the bud scar acts as a site for activating Cdc42. Somehow, expression of activated Cdc42 is by itself sufficient to polarize cells. This polarization is now shown to involve the formation of a cap of Cdc42 on the plasma membrane....