Fig. 7

A model for polarity establishment and maintenance in migrating PGCs. (A) The exit from the apolar state (i) can either be in a random direction, or biased by the polar distribution of the guidance cue. As judged by the site of actin polymerization, the cell front is defined first (ii). Actin accumulation at the front focuses the protrusions to the same location and actomyosin-dependent retrograde flow leads to progressive increase in the amount of the linker proteins (Ezrin and Esyt2a, green) and the Septin9a protein at the rear (iii). In the fully polarized cell, high levels of linker proteins are found at the cell rear (iv). (B) Polarity is maintained by the enhanced contractility at the cell front that promotes bleb formation at the front and flow of bleb-inhibiting linker proteins to the rear, where they inhibit bleb formation.