vascular connections and is conserved in all vertebrates. Very little iscurrently known about the cellular or genetic mechanisms which directthese asymmetries during cardiac morphogenesis. Molecular modifica-tions of the extracellular matrix, cellular proliferation, cell adhesion, celldifferentiation, cell migration, and cell-matrix interaction are all thoughtto be involved in thedevelopmentof cardiac asymmetries but the relativecontributions of these cellular mechanisms remain unknown. The aim ofmy project is to identify downstream genetic targets of Nodal signalingwithin the heart as well as to investigate Nodal independent factorswhich may contribute to the morphogenesis of the organ.

doi:10.1016/j.ydbio.2010.05.148

Program/Abstract # 110Endocardial-myocardial interactions direct cardiacmorphogenesisOlivier F. Noel, Nathalia Glickman HoltzmanDepartment of Biology, Queens College; City University of New York,Flushing, NY, USA

Cardiac morphogenesis has been shown to require significant coopera-tion between the endocardium and the myocardium. Previous work hasshown that proper endocardial patterning is required for propermyocardium formation. We are taking advantage of small molecule drugscreening in zebrafish to further explore the interactions between thesetwopopulations by identifying endothelial affecters. Because of itsmultipledestructive effects, we examined the consequence of FK-506 (Tacrolimus)on cardiac morphogenesis. Our data shows that FK-506 significantlydisrupts angiogenesis resulting in defects in myocardial migration andconsequently a misshapen heart tube forms. Specifically, endothelial cellswere present in treated embryos but were reduced in number andirregularly positioned. These endothelial defects result in failure of bloodcirculation and severe edema. Preliminary observations indicate linearheart tube defects consistent with early loss of endocardial-myocardialinteractions. This study supports the finding that a proper myocardium isdependent on a proper endocardium. We plan to examine the cellularbehaviors underlying these morphogenesis defects while pursuing otherdrugs of interest. We have identified another candidate drug that alsoresults in similar endocardial and myocardial defects. We hope that, takentogether, these data will provide insight into the molecular mechanismsunderlying myocardial morphogenesis. (Supported by NIH Grant: R15HL096067 to NGH, AHA Founders Affiliate Undergraduate ResearchFellowship 09-15 to ON, NIH MARC U-Star Program).

doi:10.1016/j.ydbio.2010.05.149

Program/Abstract # 111Notch-restricted Atoh1 expression regulates morphogenesis of theposterior lateral line in zebrafishMiho Matsuda, Ajay ChitnisLMG, NICHD, NIH, Bethesda, MD, USA

The posterior lateral line primordium (pLLp) migrates caudallydepositing neuromasts to establish the posterior lateral line organ inzebrafish. A Wnt-dependent FGF signaling center at the leading endof the pLLp initiates formation of “proneuromasts” by facilitating thereorganization of cells into epithelial rosettes and by initiating atoh1aexpression. Expression of atoh1a gives proneuromast cells thepotential to become sensory hair cells and lateral inhibition mediatedby Delta-Notch signaling restricts its expression to a central cell inmaturing proneuromasts. We show that as atoh1 expression becomesestablished in the central cell, it drives expression of fgf10 and theNotch ligand, deltaD, while it inhibits expression of fgfr1. As a source

of FGF10, the central cell activates the FGF pathway in neighboringcells, ensuring that they form stable epithelial rosettes. At the sametime DeltaD activates Notch in neighboring cells, inhibiting atoh1aexpression and ensuring that they are specified as supporting cells.When Notch signaling fails, unregulated atoh1a expression reducesFGFR1 expression, eventually resulting in attenuated FGF signaling,which prevents effective maturation of epithelial rosettes in the pLLp.In addition, as sensory hair cell precursors expand, atoh1a inhibits e-cadherin and this contributes to loss of cohesion and fragmentation ofthe pLLp. Together our observations reveal that restricted atoh1aexpression is essential for effective morphogenesis of the pLLp.

doi:10.1016/j.ydbio.2010.05.150

Program/Abstract # 112Studying the potential dual role of adhesion G protein-coupledreceptors in early zebrafish embryogenesisXin Lia, Heidi Hammb, Lilianna Solnica-KrezelcaNeuroscience Graduate Program, Vanderbilt University, Nashville, TN, USAbDepartment of Pharmacology, Vanderbilt University, Nashville, TN, USAcDepartment of Biological Sciences, Vanderbilt University, Nashville, TN, USA

Adhesion G protein-coupled receptors (adhesion GPCRs) are novelseven-transmembrane proteins with a large extracellular region con-taining protein modules involved in the processes of cell-cell adhesionand cell-matrix adhesion. Owing to their unique structure andinvolvement in several developmental diseases, adhesion-GPCRs areproposed to have vital dual roles in cellular adhesion and signalling.There are 33 adhesion GPCR genes in humans and 32 found so far inzebrafish. Even though the functions of most adhesion GPCRs duringembryogenesis remain uncharacterized, literature and our preliminarydata suggest that more than half of these genes are expressed duringearly zebrafish embryogenesis. We aim to delineate their expressionpatterns and to uncover their functions during early zebrafishembryogenesis. Focusing on the Group IV adhesion GPCRs, we haveidentified four members in the zebrafish genome. RT-PCR revealeddynamic temporal expression profiles of these four genes in the first fivedays of development. And they also exhibit unique spatial expressionpatterns in the first three days of development. Gain-of-function andloss-of-function experiments revealed morphogenetic defects, whichare specific to the tissues where the particular adhesion GPCR isexpressed. Based on our present data, we propose that Group IVadhesion GPCRs play important roles during early zebrafish embry-ogenesis. In the future, we will devote our efforts to determinewhetherthey functionbymediating cellular adhesion and/or signal transduction.

doi:10.1016/j.ydbio.2010.05.151

Program/Abstract # 113Proper initiation of zebrafish epiboly requires the T-boxtranscription factor Eomesodermin AAshley Bruce, Susan DuDept. of Cell & Systems Biology, Univ. of Toronto, Canada

Epiboly, or the thinning and spreadingof amultilayered cell sheet, is theearliest morphogenetic event during zebrafish development. Its first phaseinvolves doming of the yolk cell up into the overlying blastoderm. Wepreviously showed that over-expression of dominant-negative eomesoder-min a inhibits doming. Herewe report our analysis of embryos lacking bothmaternal and zygotic Eomesodermin A (MZeomesa). We find that epibolyinitiation is delayed in MZeomesa mutant embryos and, when domingoccurs, it is uneven and irregular. We are currently investigating themechanisms underlying these epiboly defects. The yolk cell microtubules,

449Abstracts

thought to provide themotive force for epiboly, are defective inMZeomesamutant embryos. Prior to doming, the yolk microtubules are abnormallybundled, leaving large regions entirelydevoid ofmicrotubules. Importantly,both thedomingdelayandtheyolkmicrotubuledistributionare rescuedbyinjection of eomesa mRNA into embryos at the 1-cell stage. In addition tothe yolk defects, the deep cells of the blastoderm display abnormalmorphologies. The deep cells are more tightly packed and exhibit morebleb-like protrusions than cells in control embryos. Transplantation studiesare being conducted to determine if the deep cell defects are cellautonomous or non-cell autonomous. Our continued investigation of thebasis of the defects in MZeomesa mutant embryos should provide newinsights into themolecular control of epiboly. Eomesodermin has also beenimplicated in gastrulation movements in both Xenopus andmice, pointingto a conserved role in regulating morphogenesis.

doi:10.1016/j.ydbio.2010.05.152

Program/Abstract # 114The cytoplasmic tyrosine kinase Arg regulates Xenopusgastrulation via the adaptor protein CrkIIChenbei Chang, Jason Fletcher, Harshit Dwivedi,Madhav Devani, Gustavo BonacciDept. Cell Biology, Univ. Alabama at Birmingham, Birmingham,AL 35294, USA

Coordinated cellmovements during vertebrate gastrulation are crucialfor correct placement of embryonic tissues along body axes and arecontrolled by multiple signals. While non-canonical Wnt pathway isshown to regulate cell polarity and directional cell behaviors via thecytoplasmic protein Dishevelled, the mechanisms used by receptortyrosine kinases, such as PDGFR, FGFR andErbBs, tomodulate gastrulationare less understood. Here, we show that the actin-binding cytoplasmictyrosine kinase Arg modulates cell movements during Xenopus gastrula-tion. Arg was expressed in dorsal tissues at the onset of gastrulation, andboth gain- and loss-of-function of Arg disrupted gastrulation movementsand led to defective frog tadpoles. Overexpression of Arg inhibited headmesoderm migration effectively, while reduction of Arg by specificantisense morpholino oligos caused aberrant head mesoderm migration,resulting in reduced migratory distance and increased cell dissociation.Both overexpression and depletion of Arg also affected convergentextension movements. The regulation of Xenopus gastrulation by Argrequired an intact kinase domain, but the actin-binding motif could bedispensed. Arg controlled phosphorylation of endogenous CrkII, anadaptor protein involved in activation of Rho family GTPases and actinreorganization. Our data thus imply that Argmaybe an essentialmediatorof receptor tyrosine kinases during gastrulation and can modulate cellmovements via phosphorylation of an important effector CrkII.

doi:10.1016/j.ydbio.2010.05.153

Program/Abstract # 115Fritz regulates the membrane stability mediated by septinsdynamics during Convergent Extension in Xenopus embryoAsako Shindo, Tae Joo Park, Su Kyoung Kim, John B. WallingfordMolecular Cell andDevelopmental Biology, University of Texas at Austin, USA

The Planar Cell Polarity (PCP) pathway is acritical regulator for cellbehaviors during development. Although there isaccumulating datashowing that core PCP proteins are necessary for cellpolarity, muchless is known about how individual cells respond to PCP signalandchange their behavior. Fritz is one of the PCP effector proteins,whichacts downstream of the core PCP proteins to control specificprocesses in Drosophila. We investigated the function of Fritz to unveil

the processbetween core PCP and the changing of cell behavior duringConvergent Extensionin Xenopus embryos. We found that Fritzwasexpressed in the dorsal mesoderm, and GFP fused Fritz localizedat the cellmembrane. Inhibition of Fritz function using antisensemor-polino-oligonucleotides (MO) lead to the gastrulation defects andabnormalcell membrane dynamics (undulation and appearance ofblebs). We found thatFritz physically interacted with septins, cytoske-letal elements that providecortical rigidity. Septins–MOs causedblastopore closure and cell behaviordefects similar to Fritz-MO. Also,GFP-fused septins localized in or near thecell membrane dependingon Fritz. Importantly, the cell elongation wasattenuated in all thesemorphants, but the medio-lateral polarity wasmaintained as inwild type embryos. From these results, we conclude that Fritzregulatesseptins, as the executants of the PCP pathway to control themembranestability and cell elongation during Convergent Extension.

doi:10.1016/j.ydbio.2010.05.154

Program/Abstract # 116Serotonin and Wnt signaling are required for morphogenesis ofthe gastrocoel roof plate epithelium, the site of symmetrybreakage in the frog embryoTina Beyera, Philipp Vicka,c, Thomas Thumbergera, Mike Danilchikb,Bärbel Ulmera, Peter Walenteka, Philipp Andrea, Susanne Boguscha,Martin Bluma, Axel SchweickertaaInstitute of Zoology, University of Hohenheim, Garbenstrasse 30,D-70593 Stuttgart, GermanybDepartment of Integrative Biosciences,Oregon Health & Science University, Portland, OR 97239, USAcHoward Hughes Medical Institute, University of California,Los Angeles CA 90095, USA

Organ laterality in vertebrates results from asymmetric signaling inthe embryo. Symmetry breakage in fish, amphibian and mammalianembryos depends on cilia-driven flow of extracellular fluid duringneurulation. In Xenopus a functionally relevant asymmetry of serotoninlocalization was postulated already at the 16-cell stage. We report therole of serotonin signaling in the context of flow. Flow, and consequentlyasymmetry, were lost in embryos in which serotonin signaling wasdownregulated, either in receptor morphants or by sequestration ofextracellular serotonin upon expression of a secreted serotonin-bindingdomain. Serotonin signaling was required for the specification of theciliated gastrocoel roof plate (GRP) epithelium during gastrulation, thesite of leftward flow. A second pathway involved in this process iscanonical Wnt signaling, as shown by flow and laterality defects inreceptor (fz8) morphants. Our data suggest that serotonin acts as apermissive and Wnt as an instructive signal to specify the GRP.

doi:10.1016/j.ydbio.2010.05.155

Program/Abstract # 117Development of swimming regulation systems in sea urchin:From blastulae to larvaeHideki Katow, Shio OokaRes. Centr. Marine Biol., Tohoku Univ., Aomori, Aomori, Japan

In sea urchin embryos, motile cilia are evident from the blastula stage,and rotatory movement by embryos can be observed in the fertilizationenvelope. Serotonin plays a role in the regulation of the beating of larvalcilia. The serotonergic nervous system is yet to appear in blastulae. Thus,the regulation system of cilia of blastulae is unknown. Nevertheless, theswimmingbehavior of blastulae is organized to a considerable degree. Thebeating of cilia is regulated also by dopamine (DA) in invertebrates and

450 Abstracts