Fig. 6: Summary.

The scheme on the left (A) is a graphical summary of the present study: the expression of the constitutively active PAK3 kinase is responsible for IN morphological changes schematized by red cells and trajectory re-orientations in the upper and lower cortical layers figured by the thick red lines; the expression of a non-activable PAK3 kinase is responsible for opposite morphological changes schematized by blue cells and for the formation of large tangential migratory streams of INs figured by the thick blue lines. Centrosome in green and myosin 2B filaments in orange. The scheme on the right (B) is an interpretative model of our results. The transient activation of PAK3 kinase in a subset of tangentially migrating INs disrupts the cell polarity and leading process stability in these cells, thereby preparing them to respond to extrinsic guidance cues that promote their re-orientation away from the tangential streams towards the cortical plate. By contrast, INs with inactive PAK3 should maintain a tangential progression.