Cell polarity, asymmetric division, and cell fate determination in brown algal zygotes

Fucus zygotes are symmetrical at fertilization. During the first cell cycle, a polar axis is generated that can be oriented by external gradients. This polar axis defines the orientation of zygotic growth, the plane of the first cell division, the distinct fates of the asymmetric daughter cells and the polarity of the organism. Establishment of polarity involves the generation of labile asymmetries in the zygote (axis formation), the stabilization of the asymmetries (axis fixation), and the separation of these asymmetries ito two daughter cells (fate determination). The actin cytoskeleton and the cell wall paly critical roles in these processes. A model postulating signaling between the cell wall and cytoplasm is presented.