Molecular Mechanisms of Development

Gastrulation is a key stage of embryonic development common to all vertebrates (Photo 1). It is characterized by induction of the mesodermal layer and by commitment of cell movements. Both these events are responsible for the arrangement of germ layers and for morphogenesis of organisms. Our goal is to understand how the signaling pathway activated by FGF is involved in these processes. FGF is known to be involved in inducing expression of mesodermal genes by activating the branch Ras / MAP kinase, and also in controlling morphogenetic movements by the branching of Ras / RalGDS / Ral (Photo 4).

Having shown the involvement of the Ral protein in gastrulation and its effect on the dynamics of the actin cytoskeleton (Photo 2), we are interested in the role of its effector. To study the function RLIP on the migration of mesendodermal cells, we developed a strategy of ex vivo explants. In these explants, we monitor, the community and individual behavior of cells, by video-microscopy. Thus we have shown that the two RLIP domains coding for μ2 and GAP are needed for mesendodermal cell movement. However these two domains have no effect on the convergence extension. Currently, we are investigating, first how the protein RLIP, via its GAP domain and its target Cdc42, acts on the actin cytoskeleton, and secondly what is the relationship between RLIP and the μ2 protein of AP2 clathrin endocytosis complex, and cell migration (picture 4). Finally we are studying the potential link between these two RLIP domains with the activity of integrin or cadherin, actin cytoskeleton dynamics and endocytosis.
As we have identified an RLIP mutant capable of blocking cytokinesis, we investigated whether clones, selected from two-hybrid screen with RLIP as bait, could rescue this phenotype. This led to the selection of Golgin-160 as partner of RLIP. Golgin-160 is a protein required for assembly of the Golgi apparatus. This interaction is currently being studied in parallel with Xenopus and HeLa cells 

Photo 1 - Gastrulation stages from stage 10.5 corresponding to the onset of gastrulation with the appearance of the dorsal blastoporal groove to stage 12.5 corresponding to blastopore closure.

 

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Photo 2 - A - Control embryos at the same developmental stage that (B). B - Embryos that express the dominant negative form of Ral. During the gastrulation they show an arrest of blastopore closure.

 

 

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Photo 3 -Embryos that express the dominant positive form of Ral. They show a bleaching of the animal hemisphere. This bleaching corresponds to the disruption of the cortical actin cytoskeleton.

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Photo 4 - Description of the FGF pathway during gastrulation. The left part shows the activation of the mesodermal genes expression; the right part shows the branching of Ral/RLIP and corresponds to our hypothetical model. This connection on Ras pathway is involved in morphogenic movements during gastrulation stage.

 

Selection of Publications

Identification and Characterization of the RLIP/RALBP1 Interacting Protein Xreps1 in Xenopus laevis Early Development
BOISSEL L., FILLATRE J., MOREAU J.
(2012) Plos One
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Recruitment of Cdc42 through the GAP domain of RLIP participates in remodeling of the actin cytoskeleton and is involved in Xenopus gastrulation.
BOISSEL L., HOUSSIN N., CHIKH A., RYNDITCH A., VAN HOVE L. and MOREAU J. (2007) Developmental Biology 312, 331-343
abstract

RLIP mediates downstream signaling from RalB to actin cytoskeleton during the Xenopus early development.
LEBRETON S., BOISSEL L., IOUZALEN N. and MOREAU J.
(2004) Mechanism of Development.
abstract

Control of embryonic Xenopus morphogenesis by a Ra1-GDS/Ra1 branch of the Ras signalling pathway.
LEBRETON S., BOISSEL L., MOREAU J.
(2003) Journal of .Cell.Science. 116, 4651-4662
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XCDT1, a vertebrate relative of fission yeast cdt1 protein is required for the assembly of pre-replicative complexes.
MAIORANO D., MOREAU J. and MECHALI M.
(2000) Nature 404, 622-624.
abstract

Last modified 03/12/2012

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