Shh-mediated centrosomal recruitment of PKA promotes symmetric proliferative neuroepithelial cell division.

Tight control of the balance between self-expanding symmetric and self-renewing asymmetric neural progenitor divisions is crucial to regulate the number of cells in the developing central nervous system. We recently demonstrated that Sonic hedgehog (Shh) signalling is required for the expansion of motor neuron progenitors by maintaining symmetric divisions. Here we show that activation of Shh/Gli signalling in dividing neuroepithelial cells controls the symmetric recruitment of PKA to the centrosomes that nucleate the mitotic spindle, maintaining symmetric proliferative divisions. Notably, Shh signalling upregulates the expression of pericentrin, which is required to dock PKA to the centrosomes, which in turn exerts a positive feedback onto Shh signalling. Thus, by controlling centrosomal protein assembly, we propose that Shh signalling overcomes the intrinsic asymmetry at the centrosome during neuroepithelial cell division, thereby promoting self-expanding symmetric divisions and the expansion of the progenitor pool.