xSyndecan4 (xSyn4), an essential component of focal adhe-

sion (FA), is expressed in the dorsal mesoderm and neuroecto-

derm during gastrulation in Xenopus embryos. Biochemical and

embryological experiments demonstrated that xSyn4 is required

for proper gastrulation and interacts biochemically and function-

ally with Dsh and Fz7.

Focal adhesion assembly and disassembly need to be tightly

regulated to allow cell migration. Disruption of this balance

results in defective cell migration and metastasis. A role for

non-canonical Wnt signaling in modulation of the turnover of

cell–cell adhesion molecules (e.g. E-cadherins) has been reported.

We have investigated the role of Wnt in the internalization and

stability of focal adhesion components mainly focusing on synd-

ecan4. We have found that Wnt5a activates internalization of

syn4 and decreases it half-life and agents that block non-canon-

ical Wnt signaling increases the levels of syn4 protein. Syn4 deg-

radation induced by Wnt5a is blocked by lactacystin, a

proteasome inhibitor and we have demonstrated for the first time

that Syn4 can be ubiquitinated in a Wnt-dependent manner

through a Dsh and Fz7 dependent-mechanism. The possible

effect of Wnt5a in integrin will be discussed.

doi:10.1016/j.mod.2009.06.086

03-P034

Interactions between signalling centres for anterior neural plate

patterning in Astyanax mexicanus

Karen Pottin, Sylvie Retaux

CNRS, Gif sur Yvette, France

The surface-dwelling and cave-living forms of Astyanax mexic-

anus are used as an advantageous model system in evolutionary

developmental biology. The two forms of this single species split

from a common ancestor 1 million years ago. Since then, cavefish

have evolved both regressive and constructive features. Recently,

our group has shown that Shh expression domain is expanded

throughout development. Moreover, we found that global fore-

brain patterning is not affected at later stages.

Here, we have investigated whether other forebrain signalisa-

tion centres may compensate for Shh expansion in cavefish. We

isolated Astyanax Fgf8, Bmp4 and Wnt1, three major factors

secreted by the anterior and dorsal midline signalling centres,

respectively, and analysed their spatio-temporal expression pat-

terns. A major difference between the two populations consists

in a heterochrony of Fgf8 expression, which is expressed 2–3 h

earlier in cavefish. We thus asked whether interactions between

the Shh and Fgf8 signalisation centres could explain this hetero-

chrony. We incubated cavefish with SU5402, an inhibitor of Fgf

signalling, or with cyclopamine, an inhibitor of Shh signalling

and observed effects on Shh and Fgf8 expression pattern. Our

results show that earlier expression of Fgf8 in cavefish maintains

Shh expansion in the anterior ventral midline. Moreover, we used

Lhx2, an anterior neural plate and eye marker as an index of ante-

rior neural plate patterning and morphogenesis to analyse influ-

ences of this interaction between above-cited signalisation

centres.

Taken together, our results show complex regulations between

these two signalisation centres which have some profound influ-

ences on neural plate patterning and forebrain morphogenesis.

doi:10.1016/j.mod.2009.06.087

03-P035

The influence of mechanical forces on the development of shape

in the avian knee joint

Karen Roddy1,2, Patrick J. Prendergast2, Paula Murphy1

1 Department of Zoology, School of Natural Sciences, Trinity College

Dublin, Dublin, Ireland2 Trinity Centre for Bioengineering, School of Engineering, Trinity College

Dublin, Dublin, Ireland

Embryonic muscle contractions are essential for the correct

formation of synovial joints. If in-utero muscle contractions are

reduced or absent the resulting joints can appear flattened and

fused. Also bones such as the patella can be underdeveloped or

lost. We hypothesise that the emergence of specific aspects of

3D shape in the embryonic joint are dependent on the muscle

induced mechanical stimuli to which the developing knee is

exposed during gestation.

Finite element (FE) analysis was used to model the normal

mechanical environment to which the developing embryonic

joint would be exposed. This environment was also perturbed

using Decamethonium bromide to induce immobilisation. Altera-

tions to the shape of the knee were captured using 3D imaging by

Optical Projection Tomography.

Our analyses indicate that specific features of the knee joint

are dependent on the dynamic pattern of mechanical stimuli gen-

erated by muscle contractions. Perturbation of the mechanical

environment led to alterations in the 3D shape of the avian knee

in regions identified as experiencing dynamic mechanical loading

through FE analysis.

In order to further our understanding of the mechanisms

responsible for integrating mechanical stimulation with molecu-

lar regulation of joint development, we are currently examining

the expression of candidate mechanoresponsive regulatory genes

to determine if altering the mechanical environment alters the

spatial distribution of expressing cells. We will present results

indicating that several genes involved in joint formation are influ-

enced by mechanical stimulation.

doi:10.1016/j.mod.2009.06.088

03-P036

Increased cell bond tension governs cell sorting at the Drosophila

anteroposterior compartment boundary

Katharina P. Landsberg1, Reza Farhadifar2, Jonas Ranft2,

Daiki Umetsu1, Thomas J. Widmann1, Thomas Bittig2,

Frank Julicher2, Christian Dahmann1

1 Max Planck Institute of Molecular Cell Biology and Genetics, Dresden,

Germany2 Max Planck Institute for the Physics of Complex Systems, Dresden,

Germany

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