FoxO Function Is Essential for Maintenance of Autophagic Flux and Neuronal Morphogenesis in Adult Neurogenesis.

Autophagy is a conserved catabolic pathway with emerging functions in mammalian neurodevelopment and human neurodevelopmental diseases. The mechanisms controlling autophagy in neuronal development are not fully understood. Here, we found that conditional deletion of the Forkhead Box O transcription factors FoxO1, FoxO3, and FoxO4 strongly impaired autophagic flux in developing neurons of the adult mouse hippocampus. Moreover, FoxO deficiency led to altered dendritic morphology, increased spine density, and aberrant spine positioning in adult-generated neurons. Strikingly, pharmacological induction of autophagy was sufficient to correct abnormal dendrite and spine development of FoxO-deficient neurons. Collectively, these findings reveal a novel link between FoxO transcription factors, autophagic flux, and maturation of developing neurons.

Stem cell maintenance in the adult mammalian hippocampus: a matter of signal integration?

The continuous generation of new neurons from stem cells in the hippocampal dentate gyrus is considered an important contributor to hippocampal plasticity. A prerequisite for the life-long generation of new dentate granule neurons is the maintenance of the neural stem cell pool. A number of essential molecular regulators and signals for hippocampal neural stem cell maintenance have been identified, but how these pathways interact to prevent precocious differentiation or exhaustion of the stem cell pool is currently unknown. Here, we summarize the current knowledge on the molecular regulation of the hippocampal stem cell pool and discuss the possibility that signal integration through Notch signaling controls stem cell maintenance in the adult hippocampus.

RBPJkappa-dependent signaling is essential for long-term maintenance of neural stem cells in the adult hippocampus.

The generation of new neurons from neural stem cells in the adult hippocampal dentate gyrus contributes to learning and mood regulation. To sustain hippocampal neurogenesis throughout life, maintenance of the neural stem cell pool has to be tightly controlled. We found that the Notch/RBPJκ-signaling pathway is highly active in neural stem cells of the adult mouse hippocampus. Conditional inactivation of RBPJκ in neural stem cells in vivo resulted in increased neuronal differentiation of neural stem cells in the adult hippocampus at an early time point and depletion of the Sox2-positive neural stem cell pool and suppression of hippocampal neurogenesis at a later time point. Moreover, RBPJκ-deficient neural stem cells displayed impaired self-renewal in vitro and loss of expression of the transcription factor Sox2. Interestingly, we found that Notch signaling increases Sox2 promoter activity and Sox2 expression in adult neural stem cells. In addition, activated Notch and RBPJκ were highly enriched on the Sox2 promoter in adult hippocampal neural stem cells, thus identifying Sox2 as a direct target of Notch/RBPJκ signaling. Finally, we found that overexpression of Sox2 can rescue the self-renewal defect in RBPJκ-deficient neural stem cells. These results identify RBPJκ-dependent pathways as essential regulators of adult neural stem cell maintenance and suggest that the actions of RBPJκ are, at least in part, mediated by control of Sox2 expression.

Expression of Sox11 in adult neurogenic niches suggests a stage-specific role in adult neurogenesis.

In the mammalian brain, neural stem and progenitor cells in the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus generate new neurons throughout adulthood. The generation of new functional neurons is a complex process that is tightly controlled by extrinsic signals and that is characterized by stage-specific gene expression programs and cell biological processes. The transcription factors regulating such stage-specific developmental steps in adult neurogenesis are largely unknown. Here we report that Sox11, a member of the group C Sox transcription factor family, is prominently expressed in the neurogenic areas of the adult brain. Further analysis revealed that Sox11 expression is strictly confined to doublecortin-expressing neuronally committed precursors and immature neurons but that Sox11 is not expressed in non-committed Sox2-expressing precursor cells and mature neurons of the adult neurogenic lineage. Finally, overexpression of Sox11 promotes the generation of doublecortin-positive immature neurons from adult neural stem cells in vitro. These data indicate that Sox11 is involved in the transcriptional regulation of specific gene expression programs in adult neurogenesis at the stage of the immature neuron.