During the development of the mammalian cerebral cortex, basal progenitor cells delaminate from the apical adherens junction belt of the neuroepithelium. But what are the cell biological processes that precede the delamination of these neural progenitors? On p. 95, Wieland Huttner and co-workers identify a new pre-delamination state of neuroepithelial cells in the mouse embryonic neocortex. Using electron microscopy, the researchers show that, in a subpopulation of neuroepithelial cells, the re-establishment of the primary cilium after mitosis occurs at the basolateral rather than at the apical plasma membrane. Neuroepithelial cells carrying basolateral cilia selectively express the basal progenitor marker Tbr2, they report, and delaminate from the apical adherens junction belt to become basal progenitors. Notably, overexpression of insulinoma-associated 1, a transcription factor that promotes the generation of basal progenitors, increases the proportion of neuroepithelial cells with basolateral cilia. Together, these results suggest that the re-establishment of a basolateral primary cilium is a cell biological feature that precedes neural progenitor delamination.

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