Disruption of augmin-mediated microtubule nucleation in neural stem cells causes p53-dependent apoptosis and aborts brain development.
Microtubules that assemble the mitotic spindle are generated by three different mechanisms: centrosomal nucleation, chromatin-mediated nucleation, and nucleation from the surface of other microtubules mediated by the augmin complex. Impairment of centrosomal nucleation in apical progenitors of the developing mouse brain induces p53-dependent apoptosis and causes non-lethal microcephaly. Whether disruption of non-centrosomal nucleation has similar effects is unclear. Here we show, using mouse embryos, that conditional knockout of the augmin subunit Haus6 in apical progenitors led to spindle defects and mitotic delay. This triggered massive apoptosis and complete abortion of brain development. Co-deletion of p53 rescued cell death, but brain development was still aborted. This could be explained by exacerbated mitotic errors and resulting chromosomal defects including increased DNA damage. Surviving progenitors had lost apico-basal polarity and failed to organize a pseudostratified epithelium. Thus, in contrast to the centrosomal nucleation pathway, augmin is crucial for apical progenitor mitosis, and, even in the absence of p53, for progression of brain development.