We next determined the role of endogenous FOXO1 in

the control of endogenous DCX expression. FOXO RNAi reduced the levels of endogenous SB431542 FOXO1 in neurons ( Figure 5D). Importantly, FOXO RNAi triggered a marked increase in endogenous DCX protein and mRNA levels ( Figures 5E and 5F) suggesting that FOXO RNAi leads to derepression of DCX gene expression. ChIP analyses revealed that, like SnoN1, FOXO1 also occupied the endogenous DCX promoter in granule neurons ( Figure 5G). Electrophoretic mobility shift assays revealed that recombinant FOXO1 robustly binds the putative FOXO binding sequence within the DCX promoter and mutation of key consensus nucleotides of the FOXO binding motif within the DCX promoter abrogated binding to FOXO1 ( Figure S5C). Together, these results suggest that FOXO1 directly binds the DCX promoter and represses DCX transcription in neurons. We next determined the role of FOXO1 in mediating isoform-specific functions of SnoN1 in neuronal morphology and positioning. We first assessed whether FOXO1 mimics SnoN1 in antagonizing SnoN2 function in the control of branching in primary granule neurons.

FOXO RNAi completely reversed the SnoN2 knockdown-induced increase in axon branching to baseline levels suggesting Olaparib in vivo that FOXO RNAi phenocopies the effect of SnoN1 RNAi in the control of neuronal branching (Figures 5H and 5I). We next asked whether FOXO1 controls neuronal positioning within the IGL in the cerebellar cortex in vivo. Remarkably, FOXO RNAi induced excessive migration of granule neurons within the IGL in rat pups analyzed at P12, increasing the proportion of granule neurons within the lower domain of the IGL to more than 70% as compared to 30% in control animals (Figures 5J and 5K). Thus, FOXO RNAi phenocopies the effect of SnoN1 RNAi on neuronal positioning within the IGL. Importantly, the expression of an RNAi-resistant form of FOXO1 (FOXO1-RES) 4��8C in the background of FOXO RNAi in rat pups reversed the FOXO RNAi-induced neuronal positioning phenotype in the cerebellar cortex (Figures 5L and 5M) supporting the conclusion

that the FOXO RNAi-induced neuronal positioning phenotype is the result of specific knockdown of FOXO1 in vivo. The combination of SnoN1 RNAi and FOXO RNAi in rat pups did not additively increase the proportion of granule neurons in the deepest region of the IGL (Figure S5D) suggesting that SnoN1 and FOXO1 operate in a shared pathway to regulate neuronal positioning in the cerebellar cortex in vivo. To determine the role of the SnoN1-FOXO1 interaction in the  regulation of neuronal positioning in the cerebellar cortex, we performed structure-function analyses. Deletion of the C-terminal domain of SnoN1, which is dispensable for SnoN1′s ability to interact with Smad2 (He et al., 2003 and Stroschein et al.