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Are there conserved triggers of regeneration in animals? Insights from the annelid
Platynereis dumerilii
Regeneration, the ability to restore lost parts of the body, is a widespread phenomenon in
animals. Whilst this ability is somehow limited in the classical developmental model organisms, a
variety of animals (for example sponges, cnidarians, planarians, annelids, salamanders …) are able to
regenerate complex structures, such as limbs, upon injury (for example amputation) and even in some
cases their whole body from a small piece of tissue (Grillo et al. 2016 Curr. Opin. Genet. & Dev. 40:23–
31). In many cases, an early step of regeneration is the formation of a so-called “regeneration
blastema”, a mass of undifferentiated proliferating cells that accumulate at the damaged surface
underneath the wound epithelium (Tanaka & Reddien 2011 Dev Cell. 21:172–185). One key question is
to identify the signals that trigger the initiation of the regeneration process and the formation of the
blastema. Recent studies have suggested that cell death could be a crucial event in the initiation of
regeneration : injury can indeed induce cell death and the dying cells can release signals that induce
responses, such as stimulation of proliferation, in the cells close to the damaged surface (a process
called apoptosis induced compensatory proliferation) (Vriz et al. 2014 Curr Top Dev Biol. 108:121–151).
There also evidence that cell death during regeneration is stimulated by the production of reactive
oxygen species (ROS), such as hydrogen peroxide (H2O2), by cells of the wound epithelium. ROS
have been shown to be essential for regeneration in several models and to act through the activation of
the MAPK and/or JNK pathways (Vriz et al. 2014).
In the lab, we use the annelid Platynereis dumerilii, an emerging developmental biology
model (Zantke et al. 2014 Genetics. 197:19–31) to study regeneration. After amputation of the posterior
part of their body, Platynereis worms are able to regenerate, through the formation of a regeneration
blastema, both the pygidium (the posteriormost part of the body, which bears the anus) and a
subterminal growth zone. This growth zone contains stem cells whose sustained proliferation allows
the worms to grow during most of their life (Gazave et al. 2013 Dev Biol. 382:246–267). These posterior
stem cells express about 20 genes whose orthologs are known to be expressed in pluripotent somatic
stem cells and primordial germ cells in other animals (Gazave et al. 2013). Some of these genes have
been shown to be also expressed in the blastemal cells during regeneration, suggesting the presence of
stem cells/progenitors in the regeneration blastema (unpublished observations of the team).
The aim of this M2 internship is to study the involvement of cell death, ROS and MAPK
signaling during posterior regeneration in Platynereis. The M2 student will conduct three types of
approaches.
- First, the M2 student will study, at different timepoints of the regeneration process, the in vivo
distribution of apoptotic cells (using an established TUNEL protocol), cells producing ROS
(using cell-permeable ROS-sensitive fluorescent dyes) and cells with MAPK signaling (using
an anti-diphospho-ERK antibody). These data will be correlated with those already obtained
about cell proliferation during regeneration.
- Second, the M2 student will analyze RNA-seq data for different stages of regenenation and
non-amputated worms. The student will search for differentially expressed genes that are
linked to apoptosis, ROS production and signaling, and MAPK signaling. The student will
further clone and characterize the expression during regeneration of some candidate genes
involved in the aforemntioned processes, using whole-mount in situ hybridization and qPCR.
- Third, the M2 student will perform functional analyses using well characterized and widely
used pharmacological inhibitors that block apoptosis, or ROS production, or MAPK signaling.
The effects of these inhibitors will be assessed on the overall regeneration process, cell
proliferation (using EdU labellings), cell death, ROS production, MAPK signaling, and stem
cell gene expression. To further assess the role of apoptosis, the student will test the CRISPRcas9 system to inactivate a crucial gene required for Platynereis apoptosis (the precise gene to
be inactivated will be chosen based on the transcriptomic and expression data).
Main recent publications of the team
-Gazave E., Lemaître Q., and Balavoine G. The Notch pathway in the annelid Platynereis: Insights into
chaetogenesis and neurogenesis processes. Open Biology, in press.
-Vervoort M., Meulemeester D., Béhague J., and Kerner P. (2016). Evolution of Prdm Genes in Animals:
Insights from Comparative Genomics. Mol. Biol. Evol. 33, 679-96.
-Demilly A., Steinmetz P., Gazave E., Marchand L., and Vervoort M. (2013). Involvement of the Wnt/β-catenin
pathway in neurectoderm architecture in Platynereis dumerilii. Nature Commun. 4, 1915.
-Gazave E., Béhague J., Laplane L., Guillou A., Préau L., Demilly A., Balavoine G., and Vervoort M. (2013).
Posterior elongation in the annelid Platynereis dumerilii involves stem cells molecularly related to primordial
germ cells. Dev. Biol. 382, 246-267.
-Kerner P., Degnan S.M., Marchand L., Degnan B.M., and Vervoort M. (2011). Evolution of RNA- binding
proteins in animals: Insights from genome-wide analysis in the sponge Amphimedon queenslandica. Mol Biol
Evol. 28, 2289-303.