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      Normal Development in Mice Over-Expressing the Intracellular Domain of DLL1 Argues against Reverse Signaling by DLL1 In Vivo

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          Abstract

          The Notch signaling pathway mediates the direct communication between adjacent cells and regulates multiple developmental processes. Interaction of the Notch receptor with its ligands induces the liberation of the intracellular portion of Notch (NICD) referred to as regulated intramembraneous proteolysis (RIP). NICD translocates to the nucleus, and by complexing with the DNA binding protein RBPjκ and other cofactors activates transcription of bHLH genes. RIP-like processing of various mammalian Notch ligands (DLL1, JAG1 and JAG2) and the translocation of their intracellular domains (ICDs) to the nucleus has also been observed. These observations together with effects of over-expressed ligand ICDs in cultured cells on cell proliferation, differentiation, and Notch activity and target gene expression have led to the idea that the intracellular domains of Notch ligands have signaling functions. To test this hypothesis in vivo we have generated ES cells and transgenic mice that constitutively express various versions of the intracellular domain of mouse DLL1. In contrast to other cell lines, expression of DICDs in ES cells did not block proliferation or stimulate neuronal differentiation. Embryos with ubiquitous DICD expression developed to term without any apparent phenotype and grew up to viable and fertile adults. Early Notch-dependent processes or expression of selected Notch target genes were unaltered in transgenic embryos. In addition, we show that mouse DICD enters the nucleus inefficiently. Collectively, our results argue against a signaling activity of the intracellular domain of DLL1 in mouse embryos in vivo.

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          Most cited references44

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          HPRT-deficient (Lesch-Nyhan) mouse embryos derived from germline colonization by cultured cells.

          Embryonal stem (ES) cell lines, established in culture from peri-implantation mouse blastocysts, can colonize both the somatic and germ-cell lineages of chimaeric mice following injection into host blastocysts. Recently, ES cells with multiple integrations of retroviral sequences have been used to introduce these sequences into the germ-line of chimaeric mice, demonstrating an alternative to the microinjection of fertilized eggs for the production of transgenic mice. However, the properties of ES cells raise a unique possibility: that of using the techniques of somatic cell genetics to select cells with genetic modifications such as recessive mutations, and of introducing these mutations into the mouse germ line. Here we report the realization of this possibility by the selection in vitro of variant ES cells deficient in hypoxanthine guanine phosphoribosyl transferase (HPRT; EC 2.4.2.8), their use to produce germline chimaeras resulting in female offspring heterozygous for HPRT-deficiency, and the generation of HPRT-deficient preimplantation embryos from these females. In human males, HPRT deficiency causes Lesch-Nyhan syndrome, which is characterized by mental retardation and self-mutilation.
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            Signalling downstream of activated mammalian Notch.

            Notch belongs to a family of transmembrane proteins that are widely conserved from flies to vertebrates and are thought to be involved in cell-fate decisions. In Drosophila, the Suppressor of hairless (Su(H)) gene and genes of the Enhancer of split (E(Spl)) complex, which encode proteins of the basic helix-loop-helix type have been implicated in the Notch signalling pathway. Mammalian homologues of E(Spl), such as the mouse Hairy enhancer of split (HES-1), have been isolated. Both HES-1 and the intracellular domain of murine Notch (mNotch) are able to block MyoD-induced myogenesis. Here we show that activated forms of mNotch associate with the human analogue of Su(H), KBF2/RBP-J kappa (refs 8,9) and act as transcriptional activators through the KBF2-binding sites of the HES-1 promoter.
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              Notch signaling controls multiple steps of pancreatic differentiation.

              Multiple cell types of the pancreas appear asynchronously during embryogenesis, which requires that pancreatic progenitor cell potential changes over time. Loss-of-function studies have shown that Notch signaling modulates the differentiation of these progenitors, but it remains unclear how and when the Notch pathway acts. We established a modular transgenic system to heritably activate mouse Notch1 in multiple types of progenitors and differentiated cells. We find that misexpression of activated Notch in Pdx1-expressing progenitor cells prevents differentiation of both exocrine and endocrine lineages. Progenitors remain trapped in an undifferentiated state even if Notch activation occurs long after the pancreas has been specified. Furthermore, endocrine differentiation is associated with escape from this activity, because Ngn3-expressing endocrine precursors are susceptible to Notch inhibition, whereas fully differentiated endocrine cells are resistant.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2013
                22 October 2013
                : 8
                : 10
                : e79050
                Affiliations
                [1 ]Institut für Molekularbiologie OE5250, Medizinische Hochschule Hannover, Hannover, Germany
                [2 ]Institut für Molekulare Immunologie, Helmholtz Zentrum München, Forschungszentrum für Umwelt und Gesundheit, GmbH, München, Germany
                Instituto de Medicina Molecular, Portugal
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: AG. Performed the experiments: CR KSG. Analyzed the data: CR AG. Contributed reagents/materials/analysis tools: EK. Wrote the manuscript: AG.

                Article
                PONE-D-13-28052
                10.1371/journal.pone.0079050
                3805521
                24167636
                6d20e78c-ba9e-4a84-8b5a-8981d70f083f
                Copyright @ 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 8 July 2013
                : 26 September 2013
                Funding
                This work was supported by DFG (Deutsche Forschungsgemeinschaft) grant GO449/10 to AG, and by funding of the Cluster of Excellence “From Regenerative Biology to Reconstructive Therapy”. The article processing charge was funded by means of the DFG-Project “Open Access Publishing” by the German Research Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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