Ecole doctorale "LOGIQUE DU VIVANT

Ecole Doctorale COMPLEXITE DU VIVANT – Fiche Projet CONCOURS
Nom et prénom du directeur de thèse (et si besoin du co-directeur) : YASUO, Hitoyoshi
Le directeur de thèse et le co-directeur doivent impérativement être habilités à diriger les recherches (HDR)
Coordonnées
Tel : 04 93 76 39 80
e-mail : [email protected]
Nom et prénom du co-encadrant (non HdR ) (s’il y a lieu) : HUDSON, Clare
Coordonnées Tel : 04 93 76 39 80
e-mail : [email protected]
Nom et prénom du responsable de l’équipe : YASUO, Hitoyoshi
Nombre de chercheurs et enseignants-chercheurs statutaires de l’équipe titulaires d’une HDR : 1
Nom et prénom du responsable du laboratoire : HOULISTON, Evelyn
Intitulé du laboratoire et N° d’unité : umr7009
Spécialité : Biologie du développement, Biochimie
Titre du projet de thèse : Quantitative study of an ON-OFF response of ERK signalling
Résumé du projet de thèse (1 page maximum, en anglais)
In this project, we address a long-standing problem of cell signalling: how a cell interprets a graded signal to generate a
switch-like (ON-OFF) response. The project focuses on the extracellular-signal-regulated kinase (ERK) pathway, an
evolutionary conserved signalling cascade frequently mediating Receptor Tyrosine Kinase (RTK) activation. This signalling
cascade, involving Ras, Raf and MEK, culminates in the phosphorylation and thus activation of ERK. Activated ERK, in
turn, phosphorylates and modulates a number of protein targets, including transcription factors, to alter their activity. The
ERK pathway is used repeatedly during embryonic development for patterning, cell fate determination and cell
proliferation. Aberrant control of ERK activity is associated with cancer as well as a large group of developmental
syndromes (1). Thus, precise control of ERK activity is critical in both embryonic and adult life. Despite the profound
defects associated with deregulated ERK signalling, quantitative analyses of ERK signalling in in vivo multicellular
contexts are rare and have never been conducted in relation to an ON-OFF response. In this project, we will address how the
ERK pathway exhibits an ON-OFF response to a graded fibroblast growth factor (FGF) signal in the context of developing
embryos. We will deploy an interdisciplinary approach including quantitative imaging, analytical chemistry, embryological
manipulations, and mathematical modelling.
To address our question, we will take advantage of the lineage-based embryogenesis of ascidians, in particular
Ciona intestinalis. Ascidian embryos develop with an invariant cell division pattern, enabling us to follow individual cells of
known identity at each stage of development. In this project, neural induction in ascidian embryos will be used to model the
ON-OFF response of ERK to FGF. Neural induction begins at the 32-cell stage, when ectoderm cells choose between neural
or epidermal fates depending on their response to the neural inducing FGF9 signal. Fgf9 is expressed broadly in the vegetal
hemisphere. While all sixteen ectoderm cells are in direct contact with FGF-expressing cells and are competent to respond
to the FGF signal, only four cells exhibit activation of ERK and its transcriptional target, the Otx gene, and adopt neural
fates (2). The quantification of cell surface contacts between FGF-expressing vegetal cells and ectoderm cells during neural
induction revealed that, among ectoderm cells, neural precursors have the largest area of cell contact with FGF-expressing
vegetal cells (3). Accordingly, a threshold mechanism was proposed in which a larger area of cell contact results in abovethreshold levels of FGF signal reception and hence ERK activation and neural induction. Critical to this threshold response
is antagonistic signalling mediated by the ligand/receptor pair ephrin/Eph from between the ectoderm cells themselves (our
unpublished data; 4). We has shown that ephrin-Ad is expressed in all ectoderm cells and that ephrin/Eph signals, mediated
intracellularly via p120RasGAP, act antagonistically to FGF signals, negatively regulating the ERK pathway during early
ascidian development (5,6,7). In ectoderm cells, when ephrin signals are blocked at the level of ephrin-Ad, Eph3 or
RasGAP, additional ectoderm cells respond to FGF signals, exhibit ERK activation and express Otx (our unpublished data).
Thus, the threshold response of ectoderm cells to graded FGF signals depends upon an intact ephrin/Eph/RasGAP signalling
system.
Our working hypothesis for the proposed project is that the antagonistic relationship between FGF and ephrin
signals, converging at the level of Ras, is central to the threshold response of ERK activation during ascidian neural
induction. In this project, by conducting data-driven mathematical modelling, we aim to reveal the underlying mechanism
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Ecole Doctorale COMPLEXITE DU VIVANT – Fiche Projet CONCOURS
that generates this ultrasensitive response of ERK. To this end, we will: (i) analyse quantitatively the dynamics of ERK
activation in individual ectoderm cells in various experimental settings; (ii) use these quantitative parameters to simulate
mathematical models of ascidian neural induction; (iii) test these models experimentally. The project will be conducted in
close collaboration with mathematical chemists, Drs. Geneviève Dupont (Université Libre de Bruxelles) and Sophie de Buyl
(Vrije Universiteit Brussel).
1) Rauen, 2013 Annu. Rev. Genomics Hum. Genet.
2) Bertrand et al, 2003, Cell
3) Tassy et al, 2006, Curr. Biol.
4) Ohta & Satou, 2013, PLoS Genetics
5) Picco et al, 2007, Development
6) Haupaix et al, 2013, Development
7) Haupaix et al, 2014, Dev. Biol.
Thèses actuellement en cours dans l’équipe : 0
Nom et Prénom du doctorant
Nom du directeur de thèse
Année de 1ere
inscription et
Ecole Doctorale
Financement pendant la thèse
Trois publications récentes du directeur de thèse (du co-directeur ou du co-encadrant s’il y a lieu).Mettre en gras le nom
du directeur de thèse.
1. Negishi T and Yasuo H. (2015). Distinct modes of mitotic spindle orientation align cells in the dorsal
midline of ascidian embryos. Dev. Biol. 408: 66-78.
2. Haupaix N, Stolfi A, Sirour C, Picco V, Levine M, Christiaen L, Yasuo H. (2013). p120RasGAP mediates
ephrin/Eph-dependent attenuation of FGF/ERK signals during cell fate specification in ascidian embryos.
Development 140:4347-4352.
3. Hudson C, Kawai N, Negishi T, Yasuo H. (2013). β-Catenin-driven binary fate specification segregates
germ layers in ascidian embryos. Curr. Biol. 23:491-495.
Docteurs encadrés par le directeur de thèse ayant soutenu après septembre 2010 et publications relatives à leur sujet de
thèse. Mettre en gras le nom du directeur de thèse et celui du docteur.
Date de soutenance : le 10 février 2014
Nom Prénom : HAUPAIX, Nicolas
Durée de thèse (en mois): 52 mois
Ecole Doctorale : Sciences de la Vie et de la Santé,
Université Nice Sophia Antipolis
Publications :
1. Haupaix N, Abitua PB, Sirour C, Yasuo H, Levine M, Hudson C. (2014). Ephrin-mediated restriction of
ERK1/2 activity delimits the number of pigment cells in the Ciona CNS. Dev. Biol. 394:170-80.
2. Haupaix N, Stolfi A, Sirour C, Picco V, Levine M, Christiaen L, Yasuo H. (2013). p120RasGAP mediates
ephrin/Eph-dependent attenuation of FGF/ERK signals during cell fate specification in ascidian embryos.
Development 140:4347-4352.
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