Project

regeneration; stem cells; developmental plasticity; RNA interference; high throughput sequencing; MAPK signaling pathway; WNt signaling pathway; gene regulatory network; cellular remodeling; hydra model system; evolution; hydra; cellular remodelling; homeostasis; injury; growth control; patterning; apoptosis-induced compensatory proliferation; gene regulatory networks; signaling

Lead
Lay summary
A fascinating, unanswered question in biology is how some organisms respond to injury by regenerating the lost body structure, whereas other have lost this potential. Three fundamental aspects of the problem are first, how does injury trigger a growth and patterning response? Second, what are the molecular actors that support the memory to regenerate the proper missing structure? Third, how does the regenerating tissue "read" the overall size of the animal to produce an appropriately sized structure? While some molecular pathways have been implicated, a clear mechanism linking physical injury to cellular and molecular response is lacking. Here we propose to use the freshwater Hydra polyp as regeneration model organism to tackle these questions. Indeed, Hydra is a simple animal currently emerging as a powerful model system to understand how a highly dynamic homeostasis might contribute to tissue repair and regeneration. At first we assume that the mechanisms maintaining homeostasis and those underlying regeneration need to be deciphered in parallel. To identify such mechanisms, we propose complementary strategies: first we will launch high throughput transcriptome analyses in homeostasis and regeneration contexts to take a snapshot of virtually all the transcribed genes in well-defined conditions, i.e. at determined time points during regeneration, at different locations along Hydra body column. In parallel we plan to perform a functional screen to identify the different classes of phenotypes linked to alterations of the homeostasis status and/or the regenerative potential in Hydra. For that screen we will apply the RNA interference method that offers the possibility to knock-down the expression of target genes for several days. In complement we propose more focused approaches to dissect the signaling pathways linking injury to cellular responses leading to de novo patterning. After mid-gastric bisection, apoptotic cells on the head-regenerating side appear to release signaling cues and we propose to investigate the stress-induced splicing event of the CREB transcription factor, as well as the complex activation of the Wnt pathway in head-regenerating tips. Taken collectively these results on gene regulatory networks and signaling during regeneration in Hydra will allow the regeneration field to perform systematic comparisons with the mechanisms at work in other regenerative model systems (as planarians, annelids, insect larvae, echinoderms, amphibians and teleost fish) to help uncover unifying principles of tissue repair and regeneration in eumetazoans.

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Last update: 21.02.2013

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The freshwater polyp hydra is a relatively simple animal currently emerging as a potent model system to study how cell plasticity regulates regeneration. Following mid-gastric bisection, the two hydra halves immediately initiate an asymmetric process leading to the regeneration of the missing structures in less than 3 days, thus leading to the formation of two complete animals. Interestingly, the asymmetry underlying this regenerative process is emerging very rapidly at the molecular and cellular level in two regions that were identical prior to mid-gastric bisection. As an example head regeneration requires controlled apoptosis and compensatory proliferation of distinct cell populations in head-regenerating stumps, whereas foot regeneration occurs in the absence of cell death and cell proliferation. At the signaling level, the asymmetric activation of the MAPK and Wnt3 pathways supports the early head organizer activity (Chera et al., Dev Cell 2009). To identify the genetic mechanisms underlying the establishment of a polarity and the subsequent regeneration process, we launched a RNAi screen that we plan to continue with this project. As a complementary strategy, we also want to perform a high-throughput transcriptome analysis using the illumina/Solexa method. This method allows to take a snapshot of virtually all the transcribed genes in well defined conditions, i.e. here at determined time points during regeneration and at different locations along hydra’s body column. Subsequently, customs microarrays will be produced and mRNAs from regeneration mutants generated through the RNAi feeding technique will be tested on these microarrays, permitting the dissection of the signaling pathways underlying the early cellular remodeling required for regeneration. We anticipate that insights on signaling during regenerative processes in Hydra will advance our general understanding of regeneration in other multicellular species.