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Botch promotes neurogenesis by antagonizing Notch.

ABSTRACT: Regulation of self-renewal and differentiation of neural stem cells is still poorly understood. Here we investigate the role of a developmentally expressed protein, Botch, which blocks Notch, in neocortical development. Downregulation of Botch in vivo leads to cellular retention in the ventricular and subventricular zones, whereas overexpression of Botch drives neural stem cells into the intermediate zone and cortical plate. In vitro neurosphere and differentiation assays indicate that Botch regulates neurogenesis by promoting neuronal differentiation. Botch prevents cell surface presentation of Notch by inhibiting the S1 furin-like cleavage of Notch, maintaining Notch in the immature full-length form. Understanding the function of Botch expands our knowledge regarding both the regulation of Notch signaling and the complex signaling mediating neuronal development.

SUBMITTER: Chi Z

PROVIDER: S-EPMC3331935 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Botch promotes neurogenesis by antagonizing Notch.

Chi Zhikai Z Zhang Jianmin J Tokunaga Akinori A Harraz Maged M MM Byrne Sean T ST Dolinko Andrew A Xu Jing J Blackshaw Seth S Gaiano Nicholas N Dawson Ted M TM Dawson Valina L VL

Developmental cell 20120322 4

Regulation of self-renewal and differentiation of neural stem cells is still poorly understood. Here we investigate the role of a developmentally expressed protein, Botch, which blocks Notch, in neocortical development. Downregulation of Botch in vivo leads to cellular retention in the ventricular and subventricular zones, whereas overexpression of Botch drives neural stem cells into the intermediate zone and cortical plate. In vitro neurosphere and differentiation assays indicate that Botch reg ...[more]

PMID: 22445366

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Project description:Foxg1, a winged-helix transcription factor, promotes the development of anterior neural structures; in mice lacking Foxg1, development of the cerebral hemispheres and olfactory epithelium (OE) is severely reduced. It has been suggested that Foxg1 acts by positively regulating the expression of growth factors, such as Fgf8, which support neurogenesis. However, Foxg1 also binds Smad transcriptional complexes, allowing it to negatively regulate the effects of TGFbeta family ligands. Here, we provide evidence that this latter effect explains much of the ability of Foxg1 to drive neurogenesis in the OE. We show that Foxg1 is expressed in developing OE at the same time as the gene encoding growth differentiation factor 11 (Gdf11), a TGFbeta family member that mediates negative-feedback control of OE neurogenesis. Mutations in Gdf11 rescue, to a considerable degree, the major defects in Foxg1(-/-) OE, including the early, severe loss of neural precursors and olfactory receptor neurons, and the subsequent collapse of both neurogenesis and nasal cavity formation. Rescue is gene-dosage dependent, with loss of even one allele of Gdf11 restoring substantial neurogenesis. Notably, we find no evidence for a disruption of Fgf8 expression in Foxg1(-/-) OE. However, we do observe both a failure of expression of follistatin (Fst), which encodes a secreted Gdf11 antagonist normally expressed in and around OE, and an increase in the expression of Gdf11 itself within the remaining OE in these mutants. Fst expression is rescued in Foxg1(-/-);Gdf11(-/-) and Foxg1(-/-);Gdf11(+/-) mice. These data suggest that the influence of Foxg1 on Gdf11-mediated negative feedback of neurogenesis may be both direct and indirect. In addition, defects in development of the cerebral hemispheres in Foxg1(-/-) mice are not rescued by mutations in Gdf11, nor is Gdf11 expressed at high levels within these structures. Thus, the pro-neurogenic effects of Foxg1 are likely to be mediated through different signaling pathways in different parts of the nervous system.

Project description:Building the complex vertebrate nervous system involves the regulated production of neurons and glia while maintaining a progenitor cell population. Neurogenesis starts asynchronously in different regions of the embryo and occurs over a long period of time, allowing progenitor cells to be exposed to multiple extrinsic signals that regulate the production of different cell types. Notch-mediated cell-cell signalling is one of the mechanisms that maintain the progenitor pool, however, little is known about how the timing of Notch activation is related to the cell cycle and the distinct modes of cell division that generate neurons. An essential tool with which to investigate the role of Notch signalling on cell by cell basis is the development a faithful reporter of Notch activity.Here we present a novel reporter for Notch activity based on the promoter of the well characterised Notch target chick Hes5-1, coupled with multiple elements that confer instability, including a destabilized nuclear Venus fluorescent protein and the 3' untranslated region (UTR) of Hes5-1. We demonstrate that this reporter faithfully recapitulates the endogenous expression of Hes5-1 and that it robustly responds to Notch activation in the chick neural tube. Analysis of the patterns of Notch activity revealed by this reporter indicates that although Notch is most frequently activated prior to mitosis it can be activated at any time within the cell cycle. Notch active progenitors undergoing mitosis generate two daughters that both continue to experience Notch signalling. However, cells lacking Notch activity before and during mitosis generate daughters with dissimilar Notch activity profiles.A novel Notch reporter with multiple destabilisation elements provides a faithful read-out of endogenous Notch activity on a cell-by-cell basis, as neural progenitors progress through the cell cycle in the chick neural tube. Notch activity patterns in this cell population provide evidence for distinct Notch signalling dynamics underlying different cell division modes and for the involvement of random initiation of Notch signalling within the neuroepithelium. These findings highlight the importance of single-cell analysis in the study of the complexity of Notch activity and provide new insights into the mechanisms underlying cell fate decisions in neural progenitors.

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Botch promotes neurogenesis by antagonizing Notch.

Publications

Botch promotes neurogenesis by antagonizing Notch.

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