13-P068 The role of mesogenin in mesoderm formation

MECHANISMS OF DEVELOPMENT

1 2 6 ( 2 0 0 9 ) S 1 9 5 –S 2 3 8

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of a5 nAChRs, structural subunits detected in many non-neuro-

‘‘stem” character to PSM character. In addition, mesogenin seems

nal tissues, and their contributions to signaling during pulmon-

to regulate expression of the segmentation clock gene her1.

ary development; however, are unknown. a5 was assessed by immunohistochemistry in mouse lungs from embryonic day (E)

doi:10.1016/j.mod.2009.06.541

13.5 to post-natal day (PN) 10. Transcriptional control of a5 was determined by transfection of murine pulmonary epithelial cell lines with reporter constructs containing 2.0 kb, 850 bp, or 450 bp of the mouse a5 promoter. TTF-1, a key transcription factor that controls pulmonary morphogenesis and Egr-1, a prevalent factor expressed at mid-gestation, were used to evaluate a5 regulation. a5 was initially detected in the most proximal primitive tubules at E15.5. a5 expression followed the proxi-

13-P069 A synthetic enhancer screen to elucidate the role of the Wnt/bcatenin network in vertebrate embryonic development Rodrigo M.

Young, Stephen W. Wilson, Thomas A. Hawkins,

Heather L. Stickney, Florencia Cavodeassi, UCL Screen Team

mal-distal axis and was detected throughout the lung until

Department of Cell & Developmental Biology, UCL, London, United

PN5, an early stage of alveologenesis. From PN5 to PN10, a5

Kingdom

expression decreased in the proximal airways and was exclusively observed in the peripheral lung by PN10. Co-localizing

The Wnt/b-catenin pathway works in numerous biological

staining revealed that a5 was expressed in Clara cells in the

contexts ranging from embryo development to stem cell renewal,

proximal lung and type II alveolar epithelial cells in the periph-

regeneration and cancer. How such diversity of function is

ery. Promoter mutagenesis revealed that both TTF-1 and Egr-1

achieved remains unclear. It is likely that molecules other than

individually and additively induced the transcription of a5. Exog-

the core Wnt pathway components and cross-talk from other sig-

enous TTF-1/Egr-1 also significantly induced a5 transcription.

nalling pathways are responsible for the context dependent mod-

These data demonstrate that a5 is specifically controlled in a

ulation of Wnt signalling. Understanding the interaction between

temporal and spatial manner during pulmonary morphogenesis.

the various players is thus fundamentally important for the

Ongoing research may demonstrate that specific regulation of a5

generation of tools to target cancer cells, modulate tissue regen-

in differentiating pulmonary epithelial cells is involved in nor-

eration and direct the fate of naı¨ve stem cells.

mal organogenesis.

Tcf proteins are transcription factors that integrate Wnt/ b-catenin signalling and drive the transcriptional output of

doi:10.1016/j.mod.2009.06.540

Wnt-responsive genes. They are therefore a functional bottleneck through which all the information input to the pathway must pass. To find genes that interact with and negatively modulate the Wnt pathway, we are conducting a forward enhancer genetic

13-P068 The role of mesogenin in mesoderm formation 1

2

1

Rita Fior , Julian Lewis , Leonor Sau´de 1

Instituto de Medicina Molecular e Instituto de Histologia e Biologia do,

screen. We have mutagenized a zebrafish line (tcf3a/headless) that under zygotic conditions shows no phenotype and is viable but is sensitised to mutations that enhance Wnt/b-catenin signalling. Because double knockdown of known modulators of Wnt/b-

Lisbon, Portugal

catenin signalling and headless (hdl) generates embryos with no

2

eyes, this phenotype is the main readout for our screen. After

Cancer Research UK, London, United Kingdom

screening about 100 F2 families, we have found 12 enhancers of Somitogenesis is an ideal process in which to study timing con-

hdl that display an eyeless phenotype and 2 in which the eyes

trol, since the spatial pattern of somites gives a linear record of the

degenerate. These phenotypes only emerge in the double homo-

temporal course of events. The somites are formed sequentially

zygous condition. We will present the phenotypic and molecular

from the presomitic mesoderm (PSM), at a rate (in zebrafish) of

characterization of one of these enhancers.

one pair every 30 min. It is thought that a segmentation clock that operates in the PSM controls this rhythmic generation of somites.

doi:10.1016/j.mod.2009.06.542

However, work from the Kimelman lab in zebrafish indicates that there is also another timer that controls when mesodermal progenitors enter the PSM to begin the preparations for somitogenesis;

13-P070

cells are retained in the tailbud for different lengths of time,

Wnt-Ca2+ signalling in kidney and embryonic development

according to which of a set of Tbx-family genes they express. This

Sally

suggests that mesodermal cells have a ‘‘maturity clock” to regulate

Nicholas Hastie

Burn, Anna Webb, Sandra Chiwanza, Peter Hohenstein,

their entrance into the PSM as well as an oscillatory ‘‘segmentation clock” that regulates their rhythmic behaviour once they are in the

MRC Human Genetics Unit, IGMM, Western General Hospital, Edin-

PSM and on the way to making somites. We are interested in the

burgh, United Kingdom

molecular mechanisms of these timers and in the question of whether they are coupled or not. We have focused on a key gene

A number of Wnt genes are expressed during, and known to

in mesoderm formation: mesogenin. Mesogenin is a downstream

be essential for, early kidney development. It is typically assumed

target of Wnt signaling and of the Tbx genes spadetail and notail.

that their products will act through the b-catenin Wnt signalling

Our data suggest that mesogenin is involved in a feedback loop

pathway; however, we have found expressional and functional

with the Tbx genes, possibly governing a switch from tailbud

evidence that the non-canonical Ca2+/NFAT signalling pathway