cultures, we have established the worldwide first Drosophila GC

model in which cytoskeletal dynamics can be analysed with the

wide range of genetic strategies and tools available for Drosoph-

ila. Morphological features and cytoskeletal dynamics closely

resemble those of vertebrate GCs, suggesting this model to be of

high translatable value.

We will report subcellular roles of the actin-microtubule linker

molecule Short stop (Shot; homologue of ACF7 and BPAG1) which

regulates neuronal MT organisation and axon length in depen-

dence of various F-actin regulators. Vice versa, Shot influences

also F-actin organisation, as illustrated by its impact on filopodia

formation. In this context, we have addressed basic mechanisms

of filopodia formation in Drosophila GCs and show that Arp2/3-

and formin-dependent mechanisms of filopodia formation clearly

co-exist. If both nucleators are knocked out genetically, F-actin

(and consequently filopodia) can be essentially eliminated from

such neurons – to our knowledge the first time such a condition

has been achieved in any cell. Genetic interaction studies couple

filopodia-promoting functions of both nucleators to the activity

of enabled, which is itself essential for filopodia formation. In con-

trast, activity of the G-actin binding molecule profilin is important

mainly for filopodia length, although genetic interaction with

enabled suggests also a facilitating role in filopodia formation.

Supported by: BBSRC, Wellcome Trust, FCT.

doi:10.1016/j.mod.2009.06.056

03-P004

The effects of patterning field properties on spatial organisation

of the skin

Ankita Singal1,2, Chunyan Mou2, Gerard Markx3, Kevin Painter4,

Denis Headon2

1 Faculty of Life Sciences, University of Manchester, Manchester,

United Kingdom2 Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom3 School of Engineering and Physical Sciences, Heriot-Watt University,

Edinburgh, United Kingdom4 School of Mathematical and Computer Sciences, Heriot-Watt

University, Edinburgh, United Kingdom

The patterning of hair and feather follicles requires extensive

signalling interactions between the cells of the embryonic skin.

Experimental evidence and theory suggest that the spatial

arrangement of the follicle pattern relies on a reaction-diffusion

mechanism, in which Activatory and Inhibitory pathways inter-

act resulting in spatial heterogeneity across the field. Here we

have examined the effects of wave propagation and field proper-

ties on the placode patterns of chicken and mouse embryonic

skin. In both species a wave initiating follicle formation propa-

gates across the skin. In mouse wave initiation and propagation

is an inhibitor-driven mechanism which originates from the

mammary placode. This is followed by intercalation of new folli-

cles as the embryo grows. In contrast, wave propagation in

chicken skin is a result of a travelling band of developmental

competence that limits the skin region undergoing patterning,

precluding intercalation of feather follicles behind this wave.

We measured placode pattern fidelity and found that avian skin

displays higher fidelity than mammalian skin. These morpho-

metric studies identified systematic deviations from a perfectly

hexagonal pattern in both species indicating the effects of wave

propagation and embryo growth in determining the follicle pat-

tern. Our mathematical modelling confirms that the distinct pat-

tern fidelities observed can be explained simply by overall wave

and field properties, without altering specific components

describing core cell signalling interactions in the model.

doi:10.1016/j.mod.2009.06.057

03-P005

Zebrafish epiboly as a model of vertebrate embryonic cell

rearrangement

Ashley Bruce, Rudolf Winklbauer

University of Toronto, Toronto, Ontario, Canada

In vertebrate embryos, the migration of cells within coherent

cell masses plays a prominent role in morphogenesis. However,

the mechanisms by which cells move across each other are poorly

understood. We study the process of epiboly, or the thinning and

spreading of a multilayered cell sheet, as a model system for cell

rearrangement. Epiboly is the earliest morphogenetic event dur-

ing zebrafish development, and its first phase – doming – involves

widespread intercalation of cells throughout the whole embryo. It

is generally held that intercalation in the blastoderm is a passive

consequence of the active doming of the yolk cell; however, this

notion has not been tested experimentally. To address whether

blastoderm cells are active participants in the doming process,

we developed an in vitro assay to examine their behavior in iso-

lated explants. Analysis of cell movements in both explants and

whole embryos as well as examination of phalloidin stained blas-

toderm slices by confocal microscopy suggests that some aspects

of epiboly initiation involve active rather than passive cell move-

ments. Our data suggest that cell movements seen in isolated

explants are reflective of epiboly in the embryo and that this sys-

tem can serve as a novel assay to address the mechanisms con-

trolling active intercellular movement. We are currently

investigating the molecular mechanisms that govern these active

cell movements.

doi:10.1016/j.mod.2009.06.058

03-P006

Juvenile hormone regulates metamorphosis of holometabolous

and hemimetabolous insects through Met and Kr-h1 genes

Barbora Konopova, Marek Jindra

Biology Centre ASCR, Ceske Budejovice, Czech Republic

Insect metamorphosis is a remarkable change in form at the

transition from larval to adult stages. It serves to study how hor-

mones regulate morphogenesis and how the signaling has chan-

ged during evolution. Most insects develop by holometaboly (e.g.

flies and beetles) or hemimetaboly (e.g. true bugs), where the for-

mer metamorphose in two steps via a pupal stage. Differentiation,

S68 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