Final Report Summary - RERE (Wnt/beta-Catenin Signalling Pathway Controls Reprogramming: The Basis Of Regeneration In Higher Vertebrates)
Our laboratory studied the Wnt-dependent mechanisms that control somatic cell reprogramming and tissue regeneration. Our projects are interdisciplinary, as they cross the boundaries between stem-cell biology, chromatin structure, mathematical modelling, gene network analysis, biophysics, and tissue regeneration. We tackled all our questions with different approaches and through different disciplines, which range from the nanoscale level of observation of cell functions, up to the whole mouse organ.
In particular, we showed that dynamics of the Wnt pathway are key to the maintenance of mESC pluripotency and for reprogramming induction (Marucci et al. Cell Reports 2014). We identified a new connection between the pluripotency factor Nanog and β-catenin, and demonstrated that Nanog represses the Wnt repressor Dkk1, which results in β-catenin stabilisation and activation of the Wnt pathway. Other highlights include the findings that: the “off-on” state of Wnt/β-catenin signalling is essential during early/ late reprogramming phases and that the Wnt effector Tcf1 is a repressor of senescence genes and a facilitator of mesenchymal-to-epithelial transition (Aulicino et al, Stem Cell Reports 2014).
Furthermore, using super-resolution fluorescence microscopy (stochastic optical reconstruction microscopy; STORM), in collaboration with Lakadamyali’s group (ICFO, Barcelona) we dissected out the nanoscale organisation of the nucleosome assembly in a variety of somatic and stem/ reprogrammed cells. We discovered that nucleosomes are arranged into discrete groups, which we called ‘nucleosome clutches’ (in analogy with egg clutches) and not in a regular hierarchical structure, as it was believed for a long time and is reported in textbooks. We identified a novel model of chromatin fiber assembly and the relation between the decoded structure and naïve pluripotency. We found that Wnt mESC mutants show a chromatin fiber including low dense clutches containing a low median number of nucleosomes (Ricci et al. Cell 2015).
Cell fusion is an approach to study somatic cell reprogramming, however it is also a regeneration mechanism (Sanges et al. Adv Exp Med Biol 2011). We showed that bone-marrow-derived cells can fuse with retinal neurons and Müller glia in degenerated retinas in mice. We observed transient reprogramming of the in-vivo formed hybrids and their differentiation in neurons, which can thereby functionally rescue ganglion/ amacrine cells and photoreceptors in drug-induced and genetic models of retinal degeneration (Sanges et al. Cell Reports 2013; Sanges et al., Journal of Clinical Investigation, under revision and patent WO/2013/020945). In addition, we also show that cell fusion can protect dopaminergic neurons in two mouse models of Parkinson’s disease (Altarche-Xifro et al. eBioMedicine 2016). We also identified a novel model of liver regeneration, which is dependent on the fusion of bone marrow cells with hepatocytes (Pedone et al., under revision).
In particular, we showed that dynamics of the Wnt pathway are key to the maintenance of mESC pluripotency and for reprogramming induction (Marucci et al. Cell Reports 2014). We identified a new connection between the pluripotency factor Nanog and β-catenin, and demonstrated that Nanog represses the Wnt repressor Dkk1, which results in β-catenin stabilisation and activation of the Wnt pathway. Other highlights include the findings that: the “off-on” state of Wnt/β-catenin signalling is essential during early/ late reprogramming phases and that the Wnt effector Tcf1 is a repressor of senescence genes and a facilitator of mesenchymal-to-epithelial transition (Aulicino et al, Stem Cell Reports 2014).
Furthermore, using super-resolution fluorescence microscopy (stochastic optical reconstruction microscopy; STORM), in collaboration with Lakadamyali’s group (ICFO, Barcelona) we dissected out the nanoscale organisation of the nucleosome assembly in a variety of somatic and stem/ reprogrammed cells. We discovered that nucleosomes are arranged into discrete groups, which we called ‘nucleosome clutches’ (in analogy with egg clutches) and not in a regular hierarchical structure, as it was believed for a long time and is reported in textbooks. We identified a novel model of chromatin fiber assembly and the relation between the decoded structure and naïve pluripotency. We found that Wnt mESC mutants show a chromatin fiber including low dense clutches containing a low median number of nucleosomes (Ricci et al. Cell 2015).
Cell fusion is an approach to study somatic cell reprogramming, however it is also a regeneration mechanism (Sanges et al. Adv Exp Med Biol 2011). We showed that bone-marrow-derived cells can fuse with retinal neurons and Müller glia in degenerated retinas in mice. We observed transient reprogramming of the in-vivo formed hybrids and their differentiation in neurons, which can thereby functionally rescue ganglion/ amacrine cells and photoreceptors in drug-induced and genetic models of retinal degeneration (Sanges et al. Cell Reports 2013; Sanges et al., Journal of Clinical Investigation, under revision and patent WO/2013/020945). In addition, we also show that cell fusion can protect dopaminergic neurons in two mouse models of Parkinson’s disease (Altarche-Xifro et al. eBioMedicine 2016). We also identified a novel model of liver regeneration, which is dependent on the fusion of bone marrow cells with hepatocytes (Pedone et al., under revision).