We noticed that expression of Ndel1SE, but not Ndel1SA, led to a defect on the Notch activity ( Figures 6G, 6H, and 6I), which most likely is due to the spindle orientation defect ( Figures 5B and 5C). We also examined whether the Notch targets, like Hes1, are reduced in PP4c mutant brains. Quantitative real-time

PCR revealed that the level of Hes1 mRNA is significantly reduced in PP4c mutant cortex compared to the control cortex ( Figure 6J). These results selleck products suggest that the misoriented spindle in the neural progenitors of PP4c knockouts could affect Notch signaling activity. Given that Notch signaling activity regulates neural progenitor proliferation and differentiation in the developing neocortex ( Gaiano et al., 2000 and Pierfelice et al., 2011), these data indicate that PP4c regulates neural progenitor proliferation through spindle orientation-dependent Notch signaling activity. In this study, we have examined the role of PP4c in Selleck INCB024360 regulating neural progenitor proliferation and differentiation in the mouse neocortex. Our data suggest that PP4c regulates Ndel1 phosphorylation and its interaction with Lis1 to control the orientation of the mitotic spindle in cortical progenitors.

When PP4c is deleted at the onset of neurogenesis, the resulting spindle orientation defects lead to premature differentiation of cortical progenitors into Suplatast tosilate neurons and severe defects in cortical layering and brain cytoarchitecture. When deleted at E12.5, however, these defects are no longer observed, although mitotic spindles in progenitor cells assume a random orientation. Thus, our data indicate that correct spindle orientation is essential in RGPs during a critical time window at the onset of neurogenesis to prevent differentiation of neural progenitors and the maintenance of cortical

integrity. During the initial neuroepithelial stages of cortical development (E8.5–E9.5), neural progenitors expand by dividing symmetrically. Neurogenesis ensues at E10.5 and gradually increases until E14.5, when most neuroepithelial divisions are asymmetric, generating one progenitor and one neuron or basal progenitor. This transition is accompanied by a gradual change of spindle orientation: while most mitotic spindles are parallel to the epithelial surface at E10.5, almost half of them show an oblique orientation at E14.5 (Postiglione et al., 2011). We propose that this gradual transition in spindle orientation is important to allow a gradual increase in neurogenesis rates and proper cortical morphogenesis. Upon the removal of PP4c at the onset of neurogenesis through Emx1Cre-mediated recombination, the number of progenitors with oblique orientation of the mitotic spindle was significantly increased.