collaborateurs

Wanda Christa Buzgariu

Adjoint(e) scientifique chez Régénération

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  • office 4009 (Sciences III)
  • The transcription factor Zic4 promotes tentacle formation and prevents epithelial transdifferentiation in Hydra Sci Adv 2022 Dec;8(51):eabo0694. 10.1126/sciadv.abo0694.

    résumé

    The molecular mechanisms that maintain cellular identities and prevent dedifferentiation or transdifferentiation remain mysterious. However, both processes are transiently used during animal regeneration. Therefore, organisms that regenerate their organs, appendages, or even their whole body offer a fruitful paradigm to investigate the regulation of cell fate stability. Here, we used as a model system and show that Zic4, whose expression is controlled by Wnt3/β-catenin signaling and the Sp5 transcription factor, plays a key role in tentacle formation and tentacle maintenance. Reducing expression suffices to induce transdifferentiation of tentacle epithelial cells into foot epithelial cells. This switch requires the reentry of tentacle battery cells into the cell cycle without cell division and is accompanied by degeneration of nematocytes embedded in these cells. These results indicate that maintenance of cell fate by a Wnt-controlled mechanism is a key process both during homeostasis and during regeneration.

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  • Studying Stem Cell Biology in Intact and Whole-Body Regenerating Hydra by Flow Cytometry. Methods Mol Biol 2022 ;2450():373-398. 10.1007/978-1-0716-2172-1_20.

    résumé

    The freshwater Hydra polyp is a versatile model to study whole-body regeneration from a developmental as well as a cellular point of view. The outstanding regenerative capacities of Hydra are based on its three populations of adult stem cells located in the central body column of the animal. There, these three populations, gastrodermal epithelial, epidermal epithelial, and interstitial, continuously cycle in homeostatic conditions, and their activity is locally regulated after mid-gastric bisection. Moreover, they present an unusual cycling behavior with a short G1 phase and a pausing in G2. This particular cell cycle has been studied for a long time with classical microscopic methods. We describe here two flow cytometry methods that provide accurate and reproducible quantitative data to monitor cell cycle regulation in homeostatic and regenerative contexts. We also present a cell sorting procedure based on flow cytometry, whereby stem cells expressing a fluorescent reporter protein in transgenic lines can be enriched for use in applications such as transcriptomic, proteomic, or cell cycle analysis.

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  • Cellular, Metabolic, and Developmental Dimensions of Whole-Body Regeneration in . Cold Spring Harb Perspect Biol 2021 Jul;():. cshperspect.a040725. 10.1101/cshperspect.a040725.

    résumé

    Here we discuss the developmental and homeostatic conditions necessary for regeneration. is characterized by populations of adult stem cells paused in the G2 phase of the cell cycle, ready to respond to injury signals. The body column can be compared to a blastema-like structure, populated with multifunctional epithelial stem cells that show low sensitivity to proapoptotic signals, and high inducibility of autophagy that promotes resistance to stress and starvation. Intact polyps also exhibit a dynamic patterning along the oral-aboral axis under the control of homeostatic organizers whose activity results from regulatory loops between activators and inhibitors. As in bilaterians, injury triggers the immediate production of reactive oxygen species (ROS) signals that promote wound healing and contribute to the reactivation of developmental programs via cell death and the de novo formation of new organizing centers from somatic tissues. In aging , regeneration is rapidly lost as homeostatic conditions are no longer pro-regenerative.

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  • Deficient autophagy in epithelial stem cells drives aging in the freshwater cnidarian . Development 2019 Dec;():. dev.177840. 10.1242/dev.177840.

    résumé

    possesses three distinct stem cell populations that continuously self-renew and prevent aging in However sexual animals from the cold-sensitive ( strain develop an aging phenotype upon gametogenesis induction, initiated by the loss of interstitial stem cells. Animals stop regenerating, lose their active behaviors and die within three months. This phenotype is not observed in the cold-resistant strain. To dissect the mechanisms of aging we compared the self-renewal of epithelial stem cells in these two strains and found it irreversibly reduced in aging while sustained in non-aging We also identified a deficient autophagy in epithelial cells, with a constitutive deficiency in autophagosome formation as detected with the mCherry-eGFP-LC3A/B autophagy sensor, an inefficient response to starvation as evidenced by the accumulation of the autophagosome cargo protein p62/SQSTM1, and a poorly-inducible autophagy flux upon proteasome inhibition. In the non-aging animals, the blockade of autophagy by knocking-down suffices to induce aging. This study highlights the essential role of a dynamic autophagy flux to maintain epithelial stem cell renewal and prevent aging.

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  • Combining BrdU-Labeling to Detection of Neuronal Markers to Monitor Adult Neurogenesis in Hydra. Methods Mol. Biol. 2020 ;2047():3-24. 10.1007/978-1-4939-9732-9_1.

    résumé

    The nervous system is produced and maintained in adult Hydra through the continuous production of nerve cells and mechanosensory cells (nematocytes or cnidocytes). De novo neurogenesis occurs slowly in intact animals that replace their dying nerve cells, at a faster rate in animals regenerating their head as a complete apical nervous system is built in few days. To dissect the molecular mechanisms that underlie these properties, a precise monitoring of the markers of neurogenesis and nematogenesis is required. Here we describe the conditions for an efficient BrdU-labeling coupled to an immunodetection of neuronal markers, either regulators of neurogenesis, here the homeoprotein prdl-a, or neuropeptides such as RFamide or Hym-355. This method can be performed on whole-mount animals as well as on macerated tissues when cells retain their morphology. Moreover, when antibodies are not available, BrdU-labeling can be combined with the analysis of gene expression by whole-mount in situ hybridization. This co-immunodetection procedure is well adapted to visualize and quantify the dynamics of de novo neurogenesis. Upon continuous BrdU labeling, the repeated measurements of BrdU-labeling indexes in specific cellular populations provide a precise monitoring of nematogenesis as well as neurogenesis, in homeostatic or developmental conditions.

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  • Loss of Neurogenesis in Aging Hydra. Dev Neurobiol 2019 05;79(5):479-496. 10.1002/dneu.22676. PMC6586502. NIHMS1019840.

    résumé

    In Hydra the nervous system is composed of neurons and mechanosensory cells that differentiate from interstitial stem cells (ISCs), which also provide gland cells and germ cells. The adult nervous system is actively maintained through continuous de novo neurogenesis that occurs at two distinct paces, slow in intact animals and fast in regenerating ones. Surprisingly Hydra vulgaris survive the elimination of cycling interstitial cells and the subsequent loss of neurogenesis if force-fed. By contrast, H. oligactis animals exposed to cold temperature undergo gametogenesis and a concomitant progressive loss of neurogenesis. In the cold-sensitive strain Ho_CS, this loss irreversibly leads to aging and animal death. Within four weeks, Ho_CS animals lose their contractility, feeding response, and reaction to light. Meanwhile, two positive regulators of neurogenesis, the homeoprotein prdl-a and the neuropeptide Hym-355, are no longer expressed, while the "old" RFamide-expressing neurons persist. A comparative transcriptomic analysis performed in cold-sensitive and cold-resistant strains confirms the downregulation of classical neuronal markers during aging but also shows the upregulation of putative regulators of neurotransmission and neurogenesis such as AHR, FGFR, FoxJ3, Fral2, Jagged, Meis1, Notch, Otx1, and TCF15. The switch of Fral2 expression from neurons to germ cells suggests that in aging animals, the neurogenic program active in ISCs is re-routed to germ cells, preventing de novo neurogenesis and impacting animal survival.

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  • Non-developmental dimensions of adult regeneration in Hydra. Int. J. Dev. Biol. 2018 ;62(6-7-8):373-381. 180111bg. 10.1387/ijdb.180111bg.

    résumé

    An essential dimension of 3D regeneration in adult animals is developmental, with the formation of organizers from somatic tissues. These organizers produce signals that recruit surrounding cells and drive the restoration of the missing structures (organs, appendages, body parts). However, even in animals with a high regenerative potential, this developmental potential is not sufficient to achieve regeneration as homeostatic conditions at the time of injury need to be "pro-regenerative". In Hydra, we identified four distinct homeostatic properties that provide a pro-regenerative framework and we discuss here how these non-developmental properties impact regeneration. First, both the epithelial and the interstitial-derived cells are highly plastic along the animal body, a plasticity that offers several routes to achieve regeneration. Second, the abundant stocks of continuously self-renewing adult stem cells form a constitutive pro-blastema in the central body column, readily activated upon bisection. Third, the autophagy machinery in epithelial cells guarantees a high level of fitness and adaptation to detrimental environmental conditions, as evidenced by the loss of regeneration in animals where autophagy is dysfunctional. Fourth, the extracellular matrix, named mesoglea in Hydra, provides a dynamically-patterned environment where the molecular and mechanical signals induced by injury get translated into a regenerative process. We claim that these homeostatic pro-regenerative features contribute to define the high regenerative potential of adult Hydra.

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  • Hydra, a model system for deciphering the mechanisms of aging and resistance to aging. Conn’s Handbook for models on human aging (Second Edition); Chapt. 38

    résumé

    Conn's Handbook of Models for Human Aging, Second Edition, presents key aspects of biology, nutrition, factors affecting lifespan, methods of age determination, use in research and the disadvantages/advantages of use. Using a multidisciplinary approach, this updated edition is designed as the only comprehensive, current work that covers the diversity in aging models. Chapters on comparative models explore age-related diseases, including Alzheimer's, joint disease, cataracts, cancer and obesity. Also included are new tricks and approaches not available in primary publications. This must-have handbook is an indispensable resource for researchers interested in the mechanisms of aging, gerontologists, health professionals, allied health practitioners and students.

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  • Impact of cycling cells and cell cycle regulation on Hydra regeneration. Dev. Biol. 2018 Jan;433(2):240-253. S0012-1606(17)30413-X. 10.1016/j.ydbio.2017.11.003.

    résumé

    Hydra tissues are made from three distinct populations of stem cells that continuously cycle and pause in G2 instead of G1. To characterize the role of cell proliferation after mid-gastric bisection, we have (i) used flow cytometry and classical markers to monitor cell cycle modulations, (ii) quantified the transcriptomic regulations of 202 genes associated with cell proliferation during head and foot regeneration, and (iii) compared the impact of anti-proliferative treatments on regeneration efficiency. We confirm two previously reported events: an early mitotic wave in head-regenerating tips, when few cell cycle genes are up-regulated, and an early-late wave of proliferation on the second day, preceded by the up-regulation of 17 cell cycle genes. These regulations appear more intense after mid-gastric bisection than after decapitation, suggesting a position-dependent regulation of cell proliferation during head regeneration. Hydroxyurea, which blocks S-phase progression, delays head regeneration when applied before but not after bisection. This result is consistent with the fact that the Hydra central region is enriched in G2-paused adult stem cells, poised to divide upon injury, thus forming a necessary constitutive pro-blastema. However a prolonged exposure to hydroxyurea does not block regeneration as cells can differentiate apical structures without traversing S-phase, and also escape in few days the hydroxyurea-induced S-phase blockade. Thus Hydra head regeneration, which is a fast event, is highly plastic, relying on large stocks of adult stem cells paused in G2 at amputation time, which immediately divide to proliferate and/or differentiate apical structures even when S-phase is blocked.

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  • Multi-functionality and plasticity characterize epithelial cells in Hydra. Tissue Barriers ;3(4):e1068908. 10.1080/21688370.2015.1068908. 1068908. PMC4681288.

    résumé

    Epithelial sheets, a synapomorphy of all metazoans but porifers, are present as 2 layers in cnidarians, ectoderm and endoderm, joined at their basal side by an extra-cellular matrix named mesoglea. In the Hydra polyp, epithelial cells of the body column are unipotent stem cells that continuously self-renew and concomitantly express their epitheliomuscular features. These multifunctional contractile cells maintain homeostasis by providing a protective physical barrier, by digesting nutrients, by selecting a stable microbiota, and by rapidly closing wounds. In addition, epithelial cells are highly plastic, supporting the adaptation of Hydra to physiological and environmental changes, such as long starvation periods where survival relies on a highly dynamic autophagy flux. Epithelial cells also play key roles in developmental processes as evidenced by the organizer activity they develop to promote budding and regeneration. We propose here an integrative view of the homeostatic and developmental aspects of epithelial plasticity in Hydra.

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  • Loss of neurogenesis in Hydra leads to compensatory regulation of neurogenic and neurotransmission genes in epithelial cells. Philos. Trans. R. Soc. Lond., B, Biol. Sci. 2016 Jan;371(1685):20150040. rstb.2015.0040. 10.1098/rstb.2015.0040. PMC4685579.

    résumé

    Hydra continuously differentiates a sophisticated nervous system made of mechanosensory cells (nematocytes) and sensory-motor and ganglionic neurons from interstitial stem cells. However, this dynamic adult neurogenesis is dispensable for morphogenesis. Indeed animals depleted of their interstitial stem cells and interstitial progenitors lose their active behaviours but maintain their developmental fitness, and regenerate and bud when force-fed. To characterize the impact of the loss of neurogenesis in Hydra, we first performed transcriptomic profiling at five positions along the body axis. We found neurogenic genes predominantly expressed along the central body column, which contains stem cells and progenitors, and neurotransmission genes predominantly expressed at the extremities, where the nervous system is dense. Next, we performed transcriptomics on animals depleted of their interstitial cells by hydroxyurea, colchicine or heat-shock treatment. By crossing these results with cell-type-specific transcriptomics, we identified epithelial genes up-regulated upon loss of neurogenesis: transcription factors (Dlx, Dlx1, DMBX1/Manacle, Ets1, Gli3, KLF11, LMX1A, ZNF436, Shox1), epitheliopeptides (Arminins, PW peptide), neurosignalling components (CAMK1D, DDCl2, Inx1), ligand-ion channel receptors (CHRNA1, NaC7), G-Protein Coupled Receptors and FMRFRL. Hence epitheliomuscular cells seemingly enhance their sensing ability when neurogenesis is compromised. This unsuspected plasticity might reflect the extended multifunctionality of epithelial-like cells in early eumetazoan evolution.

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  • Multifunctionality and plasticity characterize epithelial cells in Hydra DOI:10.1080/21688370.2015.1068908

    résumé

    Epithelial sheets, a synapomorphy of all metazoans but porifers, are present as 2 layers in cnidarians, ectoderm and endoderm, joined at their basal side by an extra-cellular matrix named mesoglea. In the Hydra polyp, epithelial cells of the body column are unipotent stem cells that continuously self-renew and concomitantly express their epitheliomuscular features. These multifunctional contractile cells maintain homeostasis by providing a protective physical barrier, by digesting nutrients, by selecting a stable microbiota, and by rapidly closing wounds. In addition, epithelial cells are highly plastic, supporting the adaptation of Hydra to physiological and environmental changes, such as long starvation periods where survival relies on a highly dynamic autophagy flux. Epithelial cells also play key roles in developmental processes as evidenced by the organizer activity they develop to promote budding and regeneration. We propose here an integrative view of the homeostatic and developmental aspects of epithelial plasticity in Hydra.

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  • Injury-induced immune responses in Hydra. Semin. Immunol. 2014 Aug;26(4):277-94. S1044-5323(14)00061-X. 10.1016/j.smim.2014.06.004.

    résumé

    The impact of injury-induced immune responses on animal regenerative processes is highly variable, positive or negative depending on the context. This likely reflects the complexity of the innate immune system that behaves as a sentinel in the transition from injury to regeneration. Early-branching invertebrates with high regenerative potential as Hydra provide a unique framework to dissect how injury-induced immune responses impact regeneration. A series of early cellular events likely require an efficient immune response after amputation, as antimicrobial defence, epithelial cell stretching for wound closure, migration of interstitial progenitors toward the wound, cell death, phagocytosis of cell debris, or reconstruction of the extracellular matrix. The analysis of the injury-induced transcriptomic modulations of 2636 genes annotated as immune genes in Hydra identified 43 genes showing an immediate/early pulse regulation in all regenerative contexts examined. These regulations point to an enhanced cytoprotection via ROS signaling (Nrf, C/EBP, p62/SQSMT1-l2), TNFR and TLR signaling (TNFR16-like, TRAF2l, TRAF5l, jun, fos-related, SIK2, ATF1/CREB, LRRC28, LRRC40, LRRK2), proteasomal activity (p62/SQSMT1-l1, Ced6/Gulf, NEDD8-conjugating enzyme Ubc12), stress proteins (CRYAB1, CRYAB2, HSP16.2, DnaJB9, HSP90a1), all potentially regulating NF-κB activity. Other genes encoding immune-annotated proteins such as NPYR4, GTPases, Swap70, the antiproliferative BTG1, enzymes involved in lipid metabolism (5-lipoxygenase, ACSF4), secreted clotting factors, secreted peptidases are also pulse regulated upon bisection. By contrast, metalloproteinases and antimicrobial peptide genes largely follow a context-dependent regulation, whereas the protease inhibitor α2macroglobulin gene exhibits a sustained up-regulation. Hence a complex immune response to injury is linked to wound healing and regeneration in Hydra.

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  • Robust G2 pausing of adult stem cells in Hydra. Differentiation ;87(1-2):83-99. S0301-4681(14)00011-5. 10.1016/j.diff.2014.03.001.

    résumé

    Hydra is a freshwater hydrozoan polyp that constantly renews its two tissue layers thanks to three distinct stem cell populations that cannot replace each other, epithelial ectodermal, epithelial endodermal, and multipotent interstitial. These adult stem cells, located in the central body column, exhibit different cycling paces, slow for the epithelial, fast for the interstitial. To monitor the changes in cell cycling in Hydra, we established a fast and efficient flow cytometry procedure, which we validated by confirming previous findings, as the Nocodazole-induced reversible arrest of cell cycling in G2/M, and the mitogenic signal provided by feeding. Then to dissect the cycling and differentiation behaviors of the interstitial stem cells, we used the AEP_cnnos1 and AEP_Icy1 transgenic lines that constitutively express GFP in this lineage. For the epithelial lineages we used the sf-1 strain that rapidly eliminates the fast cycling cells upon heat-shock and progressively becomes epithelial. This study evidences similar cycling patterns for the interstitial and epithelial stem cells, which all alternate between the G2 and S-phases traversing a minimal G1-phase. We also found interstitial progenitors with a shorter G2 that pause in G1/G0. At the animal extremities, most cells no longer cycle, the epithelial cells terminally differentiate in G2 and the interstitial progenitors in G1/G0. At the apical pole ~80% cells are post-mitotic differentiated cells, reflecting the higher density of neurons and nematocytes in this region. We discuss how the robust G2 pausing of stem cells, maintained over weeks of starvation, may contribute to regeneration.

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  • Guidelines for the use and interpretation of assays for monitoring autophagy. Autophagy 2012 Apr;8(4):445-544. PMC3404883.

    résumé

    In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

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  • Hydra, a versatile model to study the homeostatic and developmental functions of cell death. Int. J. Dev. Biol. 2012 ;56(6-8):593-604. 123499sr. 10.1387/ijdb.123499sr.

    résumé

    In the freshwater cnidarian polyp Hydra, cell death takes place in multiple contexts. Indeed apoptosis occurs during oogenesis and spermatogenesis, during starvation, and in early head regenerating tips, promoting local compensatory proliferation at the boundary between heterografts. Apoptosis can also be induced upon exposure to pro-apoptotic agents (colchicine, wortmannin), upon heat-shock in the thermosensitive sf-1 mutant, and upon wounding. In all these contexts, the cells that undergo cell death belong predominantly to the interstitial cell lineage, whereas the epithelial cells, which are rather resistant to pro-apoptotic signals, engulf the apoptotic bodies. Beside this clear difference between the interstitial and the epithelial cell lineages, the different interstitial cell derivatives also show noticeable variations in their respective apoptotic sensitivity, with the precursor cells appearing as the most sensitive to pro-apoptotic signals. The apoptotic machinery has been well conserved across evolution. However, its specific role and regulation in each context are not known yet. Tools that help characterize apoptotic activity in Hydra have recently been developed. Among them, the aposensor Apoliner initially designed in Drosophila reliably measures wortmannin-induced apoptotic activity in a biochemical assay. Also, flow cytometry and TUNEL analyses help identify distinctive features between wortmannin-induced and heat-shock induced apoptosis in the sf-1 strain. Thanks to the live imaging tools already available, Hydra now offers a model system with which the functions of the apoptotic machinery to maintain long-term homeostasis, stem cell renewal, germ cell production, active developmental processes and non-self response can be deciphered.

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  • Apoptotic cells provide an unexpected source of Wnt3 signaling to drive hydra head regeneration. Dev. Cell 2009 Aug;17(2):279-89. S1534-5807(09)00298-6. 10.1016/j.devcel.2009.07.014.

    résumé

    Decapitated Hydra regenerate their heads via morphallaxis, i.e., without significant contributions made by cell proliferation or interstitial stem cells. Indeed, Hydra depleted of interstitial stem cells regenerate robustly, and Wnt3 from epithelial cells triggers head regeneration. However, we find a different mechanism controlling regeneration after midgastric bisection in animals equipped with both epithelial and interstitial cell lineages. In this context, we see rapid induction of apoptosis and Wnt3 secretion among interstitial cells at the head- (but not foot-) regenerating site. Apoptosis is both necessary and sufficient to induce Wnt3 production and head regeneration, even at ectopic sites. Further, we identify a zone of proliferation beneath the apoptotic zone, reminiscent of proliferative blastemas in regenerating limbs and of compensatory proliferation induced by dying cells in Drosophila imaginal discs. We propose that different types of injuries induce distinct cellular modes of Hydra head regeneration, which nonetheless converge on a central effector, Wnt3.

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  • Autophagy in Hydra: a response to starvation and stress in early animal evolution. Biochim. Biophys. Acta 2009 Sep;1793(9):1432-43. S0167-4889(09)00082-2. 10.1016/j.bbamcr.2009.03.010.

    résumé

    The Hydra polyp provides a powerful model system to investigate the regulation of cell survival and cell death in homeostasis and regeneration as Hydra survive weeks without feeding and regenerates any missing part after bisection. Induction of autophagy during starvation is the main surviving strategy in Hydra as autophagic vacuoles form in most myoepithelial cells after several days. When the autophagic process is inhibited, animal survival is actually rapidly jeopardized. An appropriate regulation of autophagy is also essential during regeneration as Hydra RNAi knocked-down for the serine protease inhibitor Kazal-type (SPINK) gene Kazal1, exhibit a massive autophagy after amputation that rapidly compromises cell and animal survival. This excessive autophagy phenotype actually mimics that observed in the mammalian pancreas when SPINK genes are mutated, highlighting the paradigmatic value of the Hydra model system for deciphering pathological processes. Interestingly autophagy during starvation predominantly affects ectodermal epithelial cells and lead to cell survival whereas Kazal1(RNAi)-induced autophagy is restricted to endodermal digestive cells that rapidly undergo cell death. This indicates that distinct regulations that remain to be identified, are at work in these two contexts. Cnidarian express orthologs for most components of the autophagy and TOR pathways suggesting evolutionarily-conserved roles during starvation.

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  • Methods to investigate autophagy during starvation and regeneration in hydra. Meth. Enzymol. 2008 ;451():409-37. S0076-6879(08)03226-6. 10.1016/S0076-6879(08)03226-6.

    résumé

    In hydra, the regulation of the balance between cell death and cell survival is essential to maintain homeostasis across the animal and promote animal survival during starvation. Moreover, this balance also appears to play a key role during regeneration of the apical head region. The recent finding that autophagy is a crucial component of this balance strengthens the value of the Hydra model system to analyze the implications of autophagy in starvation, stress response and regeneration. We describe here how we adapted to Hydra some established tools to monitor steady-state autophagy. The ATG8/LC3 marker used in biochemical and immunohistochemical analyses showed a significant increase in autophagosome formation in digestive cells after 11 days of starvation. Moreover, the maceration procedure that keeps intact the morphology of the various cell types allows the quantification of the autophagosomes and autolysosomes in any cell type, thanks to the detection of the MitoFluor or LysoTracker dyes combined with the anti-LC3, anti-LBPA, and/or anti-RSK (ribosomal S6 kinase) immunostaining. The classical activator (rapamycin) and inhibitors (wortmannin, bafilomycin A(1)) of autophagy also appear to be valuable tools to modulate autophagy in hydra, as daily-fed and starved hydra display slightly different responses. Finally, we show that the genetic circuitry underlying autophagy can be qualitatively and quantitatively tested through RNA interference in hydra repeatedly exposed to double-stranded RNAs.

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