The balance between proliferative (self-renewing) and differentiative division of neural progenitor cells during development determines the final size of the different brain regions, but what regulates this balance? On , Magdalena Götz and colleagues reveal that the cell polarity Par-complex proteins play a key role in this important balancing act. During neurogenesis in the mouse brain, ventricular zone (VZ) progenitors enlarge the progenitor pool through proliferative division but subventricular zone (SVZ) progenitors mainly divide differentiatively to form neurons. In VZ progenitors only,Par-complex proteins are enriched at the apical surface. The researchers now show that the amount of endogenous Par-complex proteins decreases in parallel with the number of cortical progenitors during development. Overexpression of Par proteins, they report, increases the number of Pax6+self-renewing progenitors in vivo and in vitro by selectively promoting symmetric proliferative cell division; knockdown of Par3 has the opposite effect. Thus, the researchers conclude, Par-complex proteins regulate the balance between proliferation and differentiation in the developing cerebral cortex.
