03-P036 Increased cell bond tension governs cell sorting at the Drosophila anteroposterior compartment boundary

MECHANISMS OF DEVELOPMENT

1 2 6 ( 2 0 0 9 ) S 6 7 –S 1 0 6

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

Taken together, our results show complex regulations between

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

these two signalisation centres which have some profound influ-

derm during gastrulation in Xenopus embryos. Biochemical and

ences on neural plate patterning and forebrain morphogenesis.

embryological experiments demonstrated that xSyn4 is required for proper gastrulation and interacts biochemically and function-

doi:10.1016/j.mod.2009.06.087

ally with Dsh and Fz7. Focal adhesion assembly and disassembly need to be tightly regulated to allow cell migration. Disruption of this balance

03-P035

results in defective cell migration and metastasis. A role for

The influence of mechanical forces on the development of shape

non-canonical Wnt signaling in modulation of the turnover of

in the avian knee joint

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

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

We have investigated the role of Wnt in the internalization and

1

stability of focal adhesion components mainly focusing on syndecan4. We have found that Wnt5a activates internalization of syn4 and decreases it half-life and agents that block non-canonical Wnt signaling increases the levels of syn4 protein. Syn4 deg-

2

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.

Trinity Centre for Bioengineering, School of Engineering, Trinity College

Dublin, Dublin, Ireland

radation induced by Wnt5a is blocked by lactacystin, a proteasome inhibitor and we have demonstrated for the first time

Department of Zoology, School of Natural Sciences, 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

doi:10.1016/j.mod.2009.06.086

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

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joint would be exposed. This environment was also perturbed

Interactions between signalling centres for anterior neural plate

using Decamethonium bromide to induce immobilisation. Altera-

patterning in Astyanax mexicanus

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

Karen Pottin, Sylvie Re´taux

Optical Projection Tomography.

CNRS, Gif sur Yvette, France

Our analyses indicate that specific features of the knee joint are dependent on the dynamic pattern of mechanical stimuli generated by muscle contractions. Perturbation of the mechanical

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

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

anus are used as an advantageous model system in evolutionary

in regions identified as experiencing dynamic mechanical loading

developmental biology. The two forms of this single species split

through FE analysis.

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

In order to further our understanding of the mechanisms

have evolved both regressive and constructive features. Recently,

responsible for integrating mechanical stimulation with molecu-

our group has shown that Shh expression domain is expanded

lar regulation of joint development, we are currently examining

throughout development. Moreover, we found that global fore-

the expression of candidate mechanoresponsive regulatory genes

brain patterning is not affected at later stages.

to determine if altering the mechanical environment alters the

Here, we have investigated whether other forebrain signalisa-

spatial distribution of expressing cells. We will present results

tion centres may compensate for Shh expansion in cavefish. We

indicating that several genes involved in joint formation are influ-

isolated Astyanax Fgf8, Bmp4 and Wnt1, three major factors

enced by mechanical stimulation.

secreted by the anterior and dorsal midline signalling centres, respectively, and analysed their spatio-temporal expression pat-

doi:10.1016/j.mod.2009.06.088

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 heterochrony. 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

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 Ju¨licher2, Christian Dahmann1

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

1

rior neural plate patterning and morphogenesis to analyse influ-

Germany

ences of this interaction between above-cited signalisation

2

centres.

Germany

Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Max Planck Institute for the Physics of Complex Systems, Dresden,

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M E C H A N I S M S O F D E V E L O P M E N T 1 2 6 ( 2 0 0 9 ) S 6 7 –S 1 0 6

The subdivision of proliferating tissues into compartments is

cific binding partner dJun, as reducing dJun availability either by

an evolutionary conserved strategy during development of insects

dJun RNAi knockdown or by overexpression of the canonical dJun

and vertebrates. Boundaries between compartments are lineage

partner, dFos, completely suppresses ATF3 gain-of-function phe-

restrictions that keep cells of distinct fates sorted during prolif-

notypes. Our data thus identify ATF3 as a regulator of the epithe-

eration. As a result, sharp and straight interfaces between com-

lial cell replacement and as a new functional partner of Drosophila

partments are maintained. Compartment boundaries have long

Jun during development.

been recognized to position signaling centers that control patterning in diverse tissues. Signaling pathways involved in the

doi:10.1016/j.mod.2009.06.090

maintenance of compartment boundaries have been identified; however, the physical mechanisms underlying cell sorting are still unknown. Here we show, by quantitatively analyzing cell morphology and the response to laser ablating cell bonds in the developing Drosophila wing that tension is approximately fourfold increased on cell bonds along the anteroposterior compartment boundary compared to the remaining tissue. Cell bond tension is decreased in the presence of Y-27632, an inhibitor of

03-P038 Role of ectodysplasin in mammary gland development Maria Voutilainen, Marja Pummila, Ingrid Fliniaux, Marja Mikkola Institute of Biotechnology, University of Helsinki, Helsinki, Finland

Rho-kinase whose main effector is non-muscle myosin II (myosin II). Simulations using a vertex model demonstrate that a

Ectodermal organs such as hair, teeth and mammary glands

fourfold increase in local cell bond tension suffices to guide

develop through similar reciprocal interactions between the sur-

the re-arrangement of cells after cell division to maintain com-

face epithelium and the underlying mesenchyme. The growth of

partment boundaries. Our results provide a physical mechanism

mammary gland takes place in three phases: embryogenesis,

in which the local increase in myosin II dependent cell bond

puberty and pregnancy. In mouse the development begins 10.5

tension directs cell sorting at the anteroposterior compartment

days after fertilization (E10,5). By E12, five pairs of mammary buds

boundary.

are visible in conserved positions. By birth (E19) a rudimentary mammary tree with several branches has formed. Ectodysplasin

doi:10.1016/j.mod.2009.06.089

(Eda), a signaling molecule of the TNF family, is important in the formation of several ectodermal organs. Mutations that occur in the gene or its signaling pathway components cause hypohidrotic ectodermal dysplasia characterized by defects in several

03-P037 Interaction of ATF3 with dJun during morphogenesis of the Drosophila abdomen 1

2

2

3

Marek Jindra , Petra Sekyrova , Dirk bohmann , Mirka Uhirova

ectodermal organs but little is known about the function of Eda in mammary gland development. Eda null mice (Tabby) have abnormal nipples yet proper number of mammary glands whereas Eda overexpressing mice (K14-Eda) have supernumerary

1

Biology Center ASCR, Ceske Budejovice, Czech Republic

mammary glands. Here we have analyzed the mammary pheno-

2

University of Rochester Medical Center, Rochester, NY, United States

type of Eda /

3

Institute for Genetics, University of Cologne, Cologne, Germany

K14-Eda embryos and prepubertal mice have enhanced and Eda

and K14-Eda mice more in detail. We show that

null mice appear to have decreased branching. We are currently Metamorphosis of Drosophila larvae into pupae and adult flies

analyzing the molecular basis of both this phenotype, as well as

provides remarkable examples of morphogenesis that involves

searching for the mechanism behind formation of ectopic mam-

replacement of entire cell populations. Epithelia that had served

mary buds in K14-Eda mice.

larval function undergo programmed cell death while imaginal cells proliferate and differentiate to take their position. The adult

doi:10.1016/j.mod.2009.06.091

abdomen is formed by histoblasts that proliferate and spread, replacing larval epidermal cells (LECs). The LECs must delaminate from the epithelial sheet in order to free space for the new adult epidermis. Both the spreading of the histoblasts and the death of the LECs require signaling through the steroid (ecdysone) receptor. However, what other factors regulate the complex exchange of the epithelia during abdominal morphogenesis is unknown. Here, we implicate the basic region-leucine zipper (bZIP) protein ATF3, whose developmental role has not been previously charac-

03-P039 One the maintenance of the complex cusp pattern in continuously growing molars Mark Tummers, Irma Thesleff University of Helsinki, Helsinki, Finland

terized, in the abdominal epithelial cell replacement and differentiation. We show that expression of the atf3 mRNA is dynamically

All rodents have continuously growing incisors. The sibling

up- and down-regulated during metamorphosis, and its loss in

vole also has continuously growing molars. From one develop-

the LECs disturbs differentiation of the adult epidermal cells.

mental perspective these molars are very interesting: they have

Conversely, permanent maintenance of atf3 expression immor-

a complex cusp pattern which needs to be maintained over time.

talizes the LECs and precludes their extrusion and replacement

This process coincides with the postponement of root formation.

with histoblasts, thus causing incomplete closure of the adult

We show that both processes are driven by spatial regulation of

abdominal epithelium. To elicit this effect, ATF3 requires its spe-

the proliferation in the mesenchymal component of the tooth,