09-P015 Oct4 controls apical ectodermal ridge integrity and function during limb bud development

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MECHANISMS OF DEVELOPMENT

metabolic labeling of nascent rRNA transcripts was performed with

1 2 6 (2 0 0 9) S1 5 1–S 18 1

09-P012 – Withdrawn

32

P-orthophosphate. sycorax embryos show strong accumu-

lation of rRNA precursors and a decrease in 18S and 28S rRNA species, suggesting a defect in processing. In mammals, disruption of ribosome biogenesis leads to

09-P013

nucleolar stress and induction of apoptosis through activation

Birth of the Fin Bud

of the tumour suppressor, p53. To investigate whether the defects

Heiner Grandel, Michael Brand

in rRNA processing in sycoraxs845 mutants result in p53 upregulation, quantitative RT-PCR was performed. Markedly increased lev-

Biotec and CRTD, University of Technology, Dresden, Germany

els of p53, cyclinG1 and p21 mRNAs were observed. We hypothesize that the sycorax mutation results in abnormal TFIIH complex formation and/or regulation, causing abnormal RNA polymerase I mediated transcription and rRNA processing defects. We are currently exploring the mechanisms linking the rRNA processing defects in sycorax with the tissue-specific nature of its developmental abnormalities.

The vertebrate limb bud has the capacity to autonomously organize the development of an appendage, mediated through the action of signalling centers that reside in the bud itself. Analysis and cloning of zebrafish fin mutants has considerably advanced our understanding of the genetic interactions that lead to fin bud and organizer formation. Yet the initial event of limb field specification has turned out remarkably resistant to investigation.

doi:10.1016/j.mod.2009.06.340

During our analysis of the contribution of retinoic acid (RA) to fin development we have found that RA acts at different stages. Based on the analysis of the no fin mutant, that blocks 09-P011

the RA biosynthetic pathway, and on pharmacological inhibi-

Novel signals guiding endodermal progenitor cells toward a

tion of RARs, we have suggested that fin field specification is

pancreatic fate

initiated during gastrulation and that RA signalling is a neces1

1

2

Kristin Petzold , Heike Naumann , Ali H. Brivanlou , 1

Francesca M. Spagnoli

sary component of this process [Grandel etal., Development 129, 2851ff]. Difficulties about this conclusion have remained, however,

1

Max-Delbrueck-Center, Berlin, Germany

2

The Rockefeller University, New York, United States

because of the late read outs used for fin induction. We therefore search for markers of the presumptive lateral plate mesoderm that show RA dependence of this tissue already during gastrula-

Commitment of endodermal cells to pancreatic fate occurs as

tion. We find such genes and our results point to an effect of RA

a multistep process that eventually leads to the activation of the

signalling on hypoblast patterning at midgastrula stages. We

pancreatic gene expression program. While much is known about

can thus show RA dependence of pattern formation in the pec-

how the pancreas undergoes differentiation, growth and morpho-

toral fin forming tissue at a much earlier time than previously

genesis, we know little about early pancreatic specification.

shown.

In previous studies using the Xenopus system, we identified the signaling factor Shirin as a novel molecular player acting in the

doi:10.1016/j.mod.2009.06.343

time window between endoderm specification and initiation of pancreas development. The Xenopus gene shows high similarity to a unique human RhoGAP gene, named DLC2. Very little is known about the biological function of this protein and, in partic-

09-P014 – Withdrawn

ular, no embryological function has been assigned to it in mammalian species. Here, we show that Shirin is specifically expressed in the endoderm and future pancreatic rudiments from gastrulation onwards both in frog and mouse embryos, representing one the earliest markers of the pancreatic endoderm. Gain-offunction experiments performed in Xenopus indicated that Shirin alone is sufficient to induce pancreatic identity in the embryo, acting as a pancreatic instructive factor. In line with this, we observe

09-P015 Oct4 controls apical ectodermal ridge integrity and function during limb bud development Ana Raquel Toms1,2, Yolanda Gan Presmanes1, Adriana Lzaro Domnguez1, Joaquin Rodrguez-Len1,2

defects in pancreas formation upon conditional ablation of Shirin

1

gene expression in the mouse pancreatic endoderm. In particular,

Extremadura, Badajoz, Spain

Shirin conditional knockout mouse exhibits severe pancreatic

2

hypoplasia, possibly due to a reduction in number of specified

Oeiras, Portugal

Dpto. Anatomia, Biologia Celular y Zoologia Fac. Medicina, Univ. Centro Biologia de Desenvolvimento, Instituto Gulbenkian de Cincia,

pancreatic progenitors. Taken together, the gene expression profile and functional studies suggest a conserved role for Shirin at

Patterning of organs during development is controlled by the

the very early stages of the cascade of events leading to the spec-

activity of specialized groups of cells called organising centres.

ification of vertebrate pancreatic fate.

The apical ectodermal ridge (AER) is the center that controls proximo-distal outgrowth during limb development. This specialized

doi:10.1016/j.mod.2009.06.341

thickening of ectodermal cells at the tip of the limb bud is responsible for maintaining the underlying mesenchymal cells in an

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MECHANISMS OF DEVELOPMENT

undifferentiated and proliferative state. Structure of the AER is

2

maintained through a tuned balance between proliferation and

United States

S155

Gladstone Institute of Cardiovascular Disease, San Francisco, CA,

cell death. This equilibrium is genetically controlled but little is known about the molecules involved in this process. We have

In vertebrates heart morphology is varied from fish to mam-

found evidences that oct4 controls the proliferative balance

mals relating with their life style; fish have one atrium and one

within the AER cells. Overexpression of otc4 in the limb ectoderm

ventricle, amphibians have left and right atria and one ventricle,

disrupts the ratio cell death/proliferation and this activity is

almost reptiles have left and right atria and partially separated

under the control of wnt-canonical pathway. We also have found

ventricle, and birds and mammals have left and right atria

a special localization and behaviour of proliferating cells in the

and ventricles, completely separated four chambers. This fact

AER that could be a response to oct4 activity.

is well known, but molecular mechanism that provides such differences between four-chamber animals and not four-chamber

doi:10.1016/j.mod.2009.06.345

animals is unclear. Recent molecular studies by using mouse and chick have shown several transcription factors have important roles to form chambers, especially ventricular septum. To

09-P016

know the molecular mechanism of ventricular septum evolu-

Repression of Hedgehog signalling is required for the acquisition

tion, we focused on two reptiles, red slider turtle (Trachemys

of dorsolateral cell fates in the zebrafish otic vesicle

scripta elegans) and green anole (Anolis Carolinensis). Histological

Katherine Hammond, Fredericus van Eeden, Tanya Whitfield

analyses showed anole have a single ventricle heart but the turtle form small septum-like structure in the ventricle. We per-

MRC Centre for Developmental and Biomedical Genetics and Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom

formed section insitu hybridization and qRT-PCR to see the expression pattern of Tbx5 and Tbx20 in the turtle and the green anole. At early stages both Tbx5 and Tbx20 was expressed in the

In zebrafish, Hedgehog signalling from ventral midline struc-

whole ventricle in both anole and turtle, while at later stage

tures is both necessary and sufficient to specify posterior otic iden-

Tbx5 showed gradient expression with left-high and right-low

tity. A severe or complete loss of Hedgehog signalling leads to

manner in the turtle like that in mouse and chick, but not in

mirror symmetric double anterior ears, while severe overactivation

the anole. Tbx5-misexpression experiment in mice induced no

of the Hedgehog signalling pathway gives rise to mirror symmetric

septum, reptile-like ventricles. These results suggest that

double posterior ears. In contrast, in the mouse and chick otic ves-

restricted expression of Tbx5 is related with septum formation

icle, Hedgehog is required for dorsoventral patterning; anteropos-

and chamber evolution in the vertebrates.

terior effects, if present, are much less obvious. We now show, however, that while in zebrafish a loss of Hedgehog function does

doi:10.1016/j.mod.2009.06.347

not affect dorsoventral and mediolateral otic patterning, an increase in Hedgehog signalling activity causes an expansion of ventromedial otic territories at the expense of dorsolateral domains. In a panel of lines carrying mutations in inhibitors of

09-P018

Hedgehog signalling, Hedgehog pathway activity is variably

Six2 controls growth and elongation of the cranial base

increased throughout the embryo, and dorsolateral otic structures

Kirilenko Pavel1, Tavella Sara2, He Guiyuan1, Self Michelle3,

are lost or reduced. Even a relatively modest increase in Hedgehog

Oliver Guillermo3, Bobola Nicoletta1

signalling has consequences for the ear. In the most severely affected line, the ptc1)/); ptc2)/) double mutants, the inner ear is severely ventralised and medialised as well as displaying the previously reported double posterior character: markers of ventromedial otic domains (eya1, pax2a) are expanded at the expense of dorsolateral markers (dlx3b, tbx1). Overall these new data suggest

1

School of Dentistry, University of Manchester, Manchester, United

Kingdom 2

Laboratorio di Medicina Rigenerativa, Universita’ di Genova, Genova,

Italy 3

St. Jude Children’s Research Hospital, Memphis, United States

that Hedgehog signalling must be kept tightly repressed for the correct acquisition of dorsolateral cell fates in the zebrafish otic vesi-

The cranial base is essential for integrated craniofacial devel-

cle. The role of Hedgehog in zebrafish and amniote inner ear

opment and growth. It develops as a cartilaginous template that

patterning may not be as different as it at first appeared.

is replaced by bone through the process of endochondral ossification. Development of the cranial base is generally assumed to be

doi:10.1016/j.mod.2009.06.346

controlled by the same molecular mechanisms that regulate development of the appendicular skeleton; nevertheless, the identification of cranial base-specific signalling pathways is

09-P017 Molecular mechanism of chamber formation in the vertebrate hearts 1,2

Kazuko Koshiba-Takeuchi

2

, Benoit G. Bruneau ,

Jun K. Takeuchi1,2 1

Cardiovascular, Global Edge Institute, Tokyo Tech, Yokohama, Kanag-

awa, Japan

essential to clarify the mechanisms of its development, evolution and role in human disorders. The sine oculis/Six family of genes encode for six transcription factors in vertebrates, which are diversely expressed during vertebrate embryogenesis. In this work we describe a novel and specific role for Six2 in the growth and elongation of the cranial base. Six2 mutant