Noggin-expressing center

MECHANISMS OF DEVELOPMENT

1 2 6 ( 2 0 0 9 ) S 1 0 7 –S 1 1 2

S111

04-P014

at mid-neurulation enlarge Snail2 domain in vivo, without inter-

Stat3 self-regulates its activity downstream of fibroblast growth

fering with neural border formation. Finally we show that Snail2

factors to coordinate cell cycle progression and specification of

is a direct target of AP2a.

neural crest Massimo Nichane, Xi Ren, Eric Bellefroid Universite´ Libre de Bruxelles, Gosselies, Belgium

This work provides a new model for neural crest induction involving AP2a transcription factor. doi:10.1016/j.mod.2009.06.200

A complex set of extracellular signals is required for neural crest (NC) specification. However, how these signals function to coordinate cell cycle progression and differentiation remains poorly

04-P016

understood. Here, we report in Xenopus a role for Stat3 in this process

The new role of the blastula Chordin/Noggin-expressing center

downstream of FGF signaling. Depletion of Stat3 inhibited NC gene

Noriko Matsumura, Hiroki Kuroda

expression and proliferation while its overexpression expanded the NC domain and promoted cell proliferation. Stat3 was phosphorylated and activated in ectodermal cells by FGFs through FGFR4 binding. Stat3 activation was also modulated at the protein level by the transcription factors Hairy2 and Id3, Hairy2 facilitating and Id3 disrupting Stat3–FGFR4 complex formation. Furthermore, Hairy2 and Id3 expression were found to be under opposite transcriptional control by distinct levels of Stat3. Finally, the level of Stat3 activity was found also to critically regulate NC cell fate and proliferation, low levels inducing cell proliferation and differentiation and high levels promoting the maintenance of cells in an undifferentiated state.Together, our data indicate that Stat3, downstream of FGFs and under the positive and negative feedback regulation of Hairy2 and Id3, plays an essential role in the coordination of cell cycle progression and differentiation during NC specification. doi:10.1016/j.mod.2009.06.199

Shizuoka University, Shizuoka, Japan The most parts of the blastula Chordin- and Noggin-expressing (BCNE) center in early Xenopus embryo differentiate into anterior neural tissue, while the rests floor plate of neural tube and notochord via Spemann organizer at gastrula stage. In this study, we focused on the role of the BCNE center under the influence of mesodermal inducers in early embryonic development. Here we show that the treatment of mesodermal inducers could not cause elongation for the explants loosing BCNE center activity. Cell lineage studies demonstrated that the cells derived from BCNE center in Siamois-MO and Twn-MO gave rise to much of the paraxial and lateral mesoderm in middle and posterior region in intact embryos. On the other hand, transplantation of the BCNE center into UV-treated embryo was able to rescue the axis formation. Moreover, the sandwich explants using the combination of the hypothetical BCNE and Nieuwkoop centers created from presumptive ectodermal cells by microinjection of mRNAs surprisingly generated tadpole-like overall conforma-

04-P015 AP2a plays a central role in both neural border patterning and

tion containing head and tail structures. Taken together with these results, we conclude that the BCNE

neural crest induction

center is required for midline formation and works as a central

Noemie de Croze1, Anne Helene Monsoro-Burq1,2

player of whole body plan in amphibian early development.

1

Institut Curie, Orsay, France

2

College de France, Paris, France

doi:10.1016/j.mod.2009.06.201

AP2a is a transcription factor involved in many essential features of development such as epidermis differentiation, eye devel-

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opment and neural crest (NC) development. NC is a transient

The role of Zic2 and Zic5 in pre-gastrulation morphogenesis in

population of multipotent cells, specific of vertebrate embryos

the zebrafish embryo

which is induced at the neural border. NC cells undergo an epithe-

Rachel Joynes, Imelda McGonnell

lium to mesenchyme transition and migrate along defined paths to reach their final destination. In contrast to most of described tran-

RVC, London, United Kingdom

scription factors involved in NC development, AP2a is found as early as induction in NC progenitors and remains expressed in

Members of the Zic family of transcription factors are ortholo-

migrating NC cells. Studies in mice, zebrafish and xenopus have

gous to the Drosophila odd-paired (opl) segment polarity gene and

shown that AP2a play a critical role in NC formation, but the mech-

are involved in specification throughout development. Vertebrates

anisms by which AP2a interacts with other NC inducers such as

have multiple Zic genes with specific functions throughout devel-

Hairy2, Msx1, Pax3 and Zic1 and integrates growth factor signals

opment, including roles in proliferation and tissue patterning.

from surrounding tissues remained to be explored.

However, the cellular and molecular basis of Zic gene function is

Using Xenopus laevis early embryos, we show that AP2a is

largely unknown. Here we investigate the role of Zic2 and Zic5

essential at two distinct steps of NC development: AP2a is

genes in the earliest tissue specifying events in zebrafish, Danio

required downstream of FGF and WNT pathways: it cooperates

rerio. Microarray analysis of Zic2a/5 and Zic2b loss of function has

with Msx1 and Hairy2 in a feed-forward loop mechanism to allow

revealed a role for these genes prior to the onset of gastrulation.

proper formation of neural border. Moreover, AP2a also induces

Loss of Zic results in disruption of Claudins, which are key compo-

Snail2 in a Pax3 and Zic1 dependent manner. Activation of AP2a

nents of tight junctions and the mis-regulation of a number of