13-P075 Genome-wide in vivo screening and identification of potential regulators of FGF signaling in Xenopus laevis system

MECHANISMS OF DEVELOPMENT

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13-P074

13-P076

The role of Notch in the development of chick axial tissues

Retinoic acid and FGF signals pattern the LPM in the post-gas-

Shona Gray, Kim Dale

trula Xenopus embryo

University of Dundee, Dundee, Scotland, United Kingdom

Steven Deimling, Thomas Drysdale Children’s Health Research Institute, London, Ont., Canada

The axial tissues of the vertebrate embryo is a term that refers

University of Western Ontario, London, Ont., Canada

collectively to the floor plate (a cell population that lies at the ventral floor of the neural tube) and the notochord (which is a meso-

The lateral plate mesoderm (LPM) is traditionally thought to be

dermal rod of cells located immediately ventral to the floor plate).

a uniform tissue along the anterior–posterior axis in the neurula

The notochord and floor plate both secrete the morphogen signal

stage Xenopus laevis embryo, with the exception of the heart field.

Sonic Hedgehog (Shh) that patterns the dorsoventral axis of the

We describe a novel patterning event in the early LPM before the

neural tube. Moreover the ability of both tissues to induce floor

onset of elongation, which we propose is a result of opposing ret-

plate differentiation is mediated by Shh. These two tissues are

inoic acid (RA) and FGF signals. We have characterized restricted

believed to derive from a common progenitor pool which is

expression domains within the LPM along the anterior–posterior

located in Hensen’s node in the chick embryo. Hensen’s node

axis. Exposure to exogenous retinoic acid during neurulation

develops at the anterior tip of the primitive streak. Some of these

leads to a posterior expansion of our middle domain marker

progenitor cells remain in the node as resident stem cells. It is

Hand1, and a reduced size of the posterior Xsal-1 domain. Con-

unclear how the progenitor cells in Hensen’s node become com-

versely, exposure to a retinoic acid antagonist leads to smaller

mitted to either the notochord or floor plate cell fate. The Notch

domains of both our anterior marker FoxF1 and our middle mar-

signalling pathway is a key player in binary cell fate choice in

ker Hand1. The altered anterior–posterior patterning is main-

numerous other developmental contexts in the developing verte-

tained throughout development as demonstrated by altered

brate and invertebrate embryo and we have found this pathway

FoxF1 and Hand1 domains, as well as a displaced xHoxC-10

plays a role in the cell fate decision that occurs in the axial tissue

domain during later stages. Furthermore, exposure to a chemical

precursors in Hensen’s node. We also show that Notch signalling

FGF receptor inhibitor during the same period of development

modulates the response of neural cells to the morphogen Shh.

leads to posteriorly displaced domains of both of our middle and posterior LPM markers, which is also maintained during later

doi:10.1016/j.mod.2009.06.547

stages. The expression pattern of the RA synthesizing molecule RALDH2 suggests a high concentration of RA in the anterior-dorsal LPM, while the expression of FGF4 suggests active FGF signal-

13-P075 Genome-wide in vivo screening and identification of potential regulators of FGF signaling in Xenopus laevis system Siwei Zhang

ing in the posterior-ventral pole of the embryo during this window of time. We conclude that both retinoic acid and FGFs normally pattern the anterior–posterior axis with RA patterning the anterior-middle LPM, and FGF responsible for maintaining posterior fates.

The Healing Foundation Centre, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom

doi:10.1016/j.mod.2009.06.549

The signal transduction plays an important role during cell proliferation, differentiation, and fate control. Regarding to the involvement of FGF signaling during multiple development processes in Xenopus laevis, the screening of critical modulators in FGF signal transduction process is necessary in further clarifying the function and importance of FGF signal during embryogenesis. Our experiment approach is using one established X. tropicalis EST

13-P077 FGF signaling in OTIC morphogenesis C. Albert Noyes1, Xiaofen Want1, Ekaterina P. Hatch2, Suzanne L. Mansour1

database to identify specific gene functions in genome-wide scale

1

University of Utah, Salt Lake City, UT, United States

by in vivo approach. Signaling pathways to be investigated include

2

University of Rochester, Rochester, NY, United States

Nodal/TGF-b, FGF, BMP, RTK, wnt, and JAK-STAT pathways and their activities on blastula, gastrula and neurula stages. Main

Development of the inner ear proceeds through phases of

aim/purpose of the project will focus on both identifying any

placode induction, axis specification, otocyst formation, morpho-

potential molecules that are able to manipulate signal transduc-

genesis and cell type specification. FGF signaling plays dosage

tion in both general and signaling, and characterizing potential

sensitive roles in all of these processes. Fgf3, Fgf10 and Fgf8 are

regulators isolated during the screen. In a perspective, this insight

all expressed in the developing otic epithelium during morpho-

in vivo screening of key molecules that are able to manipulate the

genesis and differentiation. Fgf3 and Fgf10 global null mutants

state of activity for one or more signaling pathways shall greatly

each show distinct otic morphogenesis defects. Morphogenesis

enhance our comprehension on the mechanism of cells in inter-

of Fgf3 null inner ears is highly variable; with the most severe

preting different signals.

phenotypes being similar to those caused by mutations in genes that function from the hindbrain to direct dorsal patterning of

doi:10.1016/j.mod.2009.06.548

the otic vesicle and obscuring assessment of its function in otic epithelium. Fgf10 null inner ear phenotypes are more consistent;