Exocytosis in action

olarizing 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. P