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Barcelona, Spain

Neves J.,University Pompeu Fabra | Uchikawa M.,Osaka University | Bigas A.,Program in Cancer Research | Giraldez F.,University Pompeu Fabra
PLoS ONE | Year: 2012

The proneural gene Atoh1 is crucial for the development of inner ear hair cells and it requires the function of the transcription factor Sox2 through yet unknown mechanisms. In the present work, we used the chicken embryo and HEK293T cells to explore the regulation of Atoh1 by Sox2. The results show that hair cells derive from Sox2-positive otic progenitors and that Sox2 directly activates Atoh1 through a transcriptional activator function that requires the integrity of Sox2 DNA binding domain. Atoh1 activation depends on Sox transcription factor binding sites (SoxTFBS) present in the Atoh1 3′ enhancer where Sox2 directly binds, as shown by site directed mutagenesis and chromatin immunoprecipitation (ChIP). In the inner ear, Atoh1 enhancer activity is detected in the neurosensory domain and it depends on Sox2. Dominant negative competition (Sox2HMG-Engrailed) and mutation of the SoxTFBS abolish the reporter activity in vivo. Moreover, ChIP assay in isolated otic vesicles shows that Sox2 is bound to the Atoh1 enhancer in vivo. However, besides activating Atoh1, Sox2 also promotes the expression of Atoh1 negative regulators and the temporal profile of Atoh1 activation by Sox2 is transient suggesting that Sox2 triggers an incoherent feed-forward loop. These results provide a mechanism for the prosensory function of Sox2 in the inner ear. We suggest that sensory competence is established early in otic development through the activation of Atoh1 by Sox2, however, hair cell differentiation is prevented until later stages by the parallel activation of negative regulators of Atoh1 function. © 2012 Neves et al. Source

Bigas A.,Program in Cancer Research | Robert-Moreno A.,University Pompeu Fabra | Espinosa L.,Program in Cancer Research
International Journal of Developmental Biology | Year: 2010

The main function of the Notch signaling pathway is to generate cell diversity during both embryonic development and adult tissue homeostasis. The extended use of this pathway, together with its conservation during evolution, is indicative of its importance. During embryonic development, the vascular and hematopoietic systems are intimately associated and Notch signals are responsible for the correct specification of both systems. More explicitly, Notch is required for the induction of the arterial program; however, it is simultaneously or consecutively also involved in the generation of hematopoietic stem cells. Although both genetic programs are different, they are both implemented in endothelial cells of the dorsal aorta in the midgestation embryo. This close association during the development of arteries and blood has hindered our understanding of Notch function in the generation of hematopoietic stem cells. Here, we will review the work from recent years showing how Notch participates in the embryonic development of hematopoiesis in the mouse, but also in other organisms such as chick, zebrafish and flies. © 2010 UBC Press. Source

Lopez-Arribillaga E.,Program in Cancer Research | Rodilla V.,Program in Cancer Research | Pellegrinet L.,Ecole Polytechnique Federale de Lausanne | Guiu J.,Program in Cancer Research | And 10 more authors.
Development (Cambridge) | Year: 2015

Genetic data indicate that abrogation of Notch-Rbpj or Wnt-β-catenin pathways results in the loss of the intestinal stem cells (ISCs). However, whether the effect of Notch is direct or due to the aberrant differentiation of the transit-amplifying cells into post-mitotic goblet cells is unknown. To address this issue,we have generated composite tamoxifen-inducible intestine-specific genetic mouse models and analyzed the expression of intestinal differentiation markers. Importantly, we found that activation of β-catenin partially rescues the differentiation phenotype of Rbpj deletion mutants, but not the loss of the ISC compartment. Moreover, we identified Bmi1, which is expressed in the ISC and progenitor compartments, as a gene that is co-regulated by Notch and β-catenin. Loss of Bmi1 resulted in reduced proliferation in the ISC compartment accompanied by p16INK4aand p19ARF(splice variants of Cdkn2a) accumulation, and increased differentiation to the post-mitotic goblet cell lineage that partially mimics Notch loss-of-function defects. Finally, we provide evidence that Bmi1 contributes to ISC self-renewal. © 2015. Published by The Company of Biologists Ltd. Source

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