, 2005). Collectively, these results provide evidence that N-cadherin expression and neuroepithelial maintenance are controlled by both activating inputs provided by Sox2 and repressive inputs provided by Foxp4, mediated by distinct enhancer elements. If N-cadherin is the critical target for Foxp repression, then the same ectopic differentiation phenotype should be observed by learn more directly blocking N-cadherin activity. To this end, we misexpressed a dominant-negative form of N-cadherin (dn-N-Cad) lacking its extracellular domain, which disrupts adhesions between neighboring cells (Tanabe et al., 2006).

High levels of dn-N-cad disrupted the radial structure of the neuroepithelium, resulting in a cytoplasmic accumulation of Numb and ectopic formation of NeuN+ neurons in the VZ much like the defects seen after Foxp4 misexpression (Figures 5A, 5B, 5F, 5G, 5K, 5L, 5P, 5Q, 5U, 5V,

5Z, and 5AC). Interestingly, low-level misexpression of dn-N-cad also promoted neuronal differentiation, but under these conditions AJs and the radial structure of the neuroepithelium was preserved. The majority of these transfected cells settled in the IZ, though they rarely migrated further Antiinfection Compound Library into the MZ (Figures 5C, 5H, 5M, 5R, 5W). Misexpression of full-length N-cadherin had the opposite effect, retaining most of the transfected cells in a progenitor-like state within the VZ (Figures 5D, 5I, 5N, 5S, and 5X). Sox2 is known to activate N-cadherin expression in many regions of the CNS, and its elevation can block neuronal differentiation (Bylund et al., 2003, Graham et al., 2003 and Matsumata Org 27569 et al., 2005). We therefore examined whether Sox2 misexpression could increase N-cadherin and thereby offset the progenitor-suppressing actions of Foxp4. When Sox2 was elevated, apical staining for N-cadherin and other components of AJs such as aPKCζ and Numb was increased, reminiscent of the phenotype seen with

Foxp2 and Foxp4 knockdown (compare results in Figures 3S and 3T to Figures 5E, 5J, 5O, 5T, and 5Y). Moreover, the majority of transfected cells remained in the VZ and neuronal differentiation was blocked (Figures 5A and 5E). When Sox2 was coexpressed with Foxp4, N-cadherin levels and AJs were fully restored and cells were held in a NPC state (Figures 5Z–5AA, 5AC, 5AD, and 5AF). Identical results were obtained with the coexpression of Foxp4 with full-length N-cadherin (Figures 5AB, 5AE, 5AF). Thus, Foxp4 appears to work in opposition to Sox2 in setting the level of N-cadherin expression to balance progenitor maintenance with differentiation (Figure 5AG). We next set out to determine where Foxp4 functions in the neurogenic cascade that mediates neuronal differentiation.