03-p005 zebrafish epiboly as a model of vertebrate embryonic cell rearrangement
TRANSCRIPT
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