cally, begins in the embryo and continues throughout development toadulthood. Cardiac development in zebrafish embryos has beenstudied extensively, and recent studies looking at adult heartsindicate significant maturation, however, little is known about howthese changes take place. We hope to elucidate the mechanismsdriving cardiac maturation and develop zebrafish as a modelorganism for cardiology. It has been established that form andfunction of organs effect their development. In the heart, contractionand blood flow are some of the factors effecting the development ofthe structure of the heart. Thus far we have determined that the lackof contraction of the atrium in weak atrium mutant, which hasreduced or absent contraction of the atrium, has a clear effect onfunction and the resulting structure of the ventricle. In humanscardiomyopathy is attributed to both environmental and geneticfactors, though specific causes are often unknown. The zebrafishmutant, weak atrium, through the reduced function of the atrium,develops a cardiomyopathy-like phenotype in the ventricle. We haveexamined the maturation of heart structure and this disease state inweak atrium mutant in order to gain insight into the mechanismsregulating cardiomyopathy.

doi:10.1016/j.ydbio.2011.05.644

Program/Abstract # 231The chromatin remodeling complex subunit Baf60c regulatesessential gene expression programs in heart developmentXin Suna, John Wylieb, Yuqing Zhouc, Danos Christodouloud, ChristineE. Seidmane, Jonathan G. Seidmane, Mark Henkelmanc, Janet Rossanta,Benoit BruneaubaHospital for Sick Children, Toronto, ON, CanadabGladstone Institute of Cardiovascular Disease, San Francisco, CA, USAcMouse Imaging Centre The Hospital for Sick Children Toronto Centre forPhenogenomics, Toronto, ON, CanadadHarvard Medical School, Boston, MA, USAeDepartment of Genetics Harvard Medical School, Boston, MA, USA

SWI/SNF complexes are ATP-dependent chromatin remodelingcomplexes widely existing from yeast to mammals. In mammals theyare also called BAF (Brm/BRG1 Associating Factor) complexes.Combinations of constitutive BAF members and multiple tissue orcell type-specific BAF members can generate hundreds of differentBAF complexes. Several have been reported to play critical roles indevelopment processes including neuron differentiation and ES celldifferentiation. Baf60c is one of the three Baf60 subunits in themouse. Baf60c is highly expressed in the mouse heart from thecardiac crescent stage. Baf60c can associate with cardiac transcriptionfactors including Tbx5, Nkx2-5, and myocardin. To understand therole of Baf60c in mouse heart development, a Baf60c conditionalknockout mouse line was established and Baf60c knockout embryophenotypes were characterized. Constitutive loss of Baf60c results inhypoplastic myocardium and embryonic death by E14.5. RNA-seq ofE12.5 Baf60c knockout embryo hearts shows a broad down-regula-tion of mitochondria encoded or related genes, as well as cardio-myocyte sarcomere and contraction apparatus genes, indicatingmitochondrial biogenesis defects and cardiomyocyte sarcomereassembly or function defects. High frequency echocardiographyshowed that Baf60c knockout embryo ventricle walls are hypocon-tractile. Transmission electron microscopy showed that Baf60cknockout cardiomyocytes have disarrayed myofibers. Deletion ofBaf60c with Myh6::Cre in cardiomyocytes also causes abnormal heartgrowth. Many of Myh6::Cre, Baf60cflx/− pups showed retardedgrowth and only some of them can survive to adulthood. Histologyand echocardiography showed that these mice have thinner ventriclewalls and dilated chambers. In summary, Baf60c is a cardiac-specific

chromatin-remodeling factor that has critical functions in bothembryonic and postnatal heart growth. The mechanism of Baf60cfunction in regulating cardiac growth in conjunction with transcrip-tion factors and other chromatin remodeling complexes remains tobe elucidated.

doi:10.1016/j.ydbio.2011.05.645

Program/Abstract # 232Cardiac valve malformations: New insights from Pdlim7, anunexpected suspect in heart developmentJennifer Krcmerya, Rudyard Sadleirb, Rajesh Guptaa, Chrissy Kamidea,Sol Misenera, Douglas Losordoa, Hans-Georg Simona

aNorwestern Univ., Chicago, IL, USAbChicago, USA

PDZ-LIM proteins contain multiple binding domains, facilitatinginteractions with the actin cytoskeleton, nuclear factors, andsignaling molecules, thereby allowing the proteins to carry outdiverse biological functions. Here, we characterize a new familymember, Pdlim7, which in zebrafish revealed important functionsduring cardiac and limb development. In order to determine the roleof Pdlim7 in a mammalian four-chambered heart from early valveformation all the way to fully functioning adult valves, we generated aPdlim7 knock-out mouse. Pdlim7 null embryos demonstrate mis-regulation of molecular and cellular processes necessary during earlyvalve formation. These developmental problems translate intoaberrant shaped heart valves in adult mice as demonstrated byquantitative measurements obtained from 3-dimensional reconstruc-tions of serial heart sections. Utilizing echocardiography, we are ableto visualize the physiological consequences of these structuralabnormalities, which include increased mitral valve annulus dimen-sion and subtle left ventricular dysfunction. This work identifies theactin-associated protein Pdlim7 as an unexpected and novel factorcritical for mammalian cardiac valve development and maturation.Thus, the Pdlim7 knock-out mouse may provide a new model forstudying cardiac valve disease progression from the embryo to theadult.

doi:10.1016/j.ydbio.2011.05.646

Program/Abstract # 233Proteomic analysis of cardiovascular development in the Ts65DnDown Syndrome mouse modelClara S. Moorea, Erik Kellyb, Arianna FrancabaFranklin and Marshall College Biology, Lancaster, PA, USAbFranklin & Marshall College, Lancaster, PA, USA

Down Syndrome (DS) due to triplication of human chromosome21 (Hsa21) results in congenital heart defects in 50% of newbornswith DS. The Mus musculus Ts65Dn model, with triplication ofapproximately 132 genetic orthologs to Hsa 21, has multiple DSphenotypes such as neonatal lethality and cardiovascular defects.Dosage imbalance of Ts65Dn embryos may cause misexpression ofnot only triplicated genes, but many other genes contributing to theobserved cardiovascular abnormalities. We utilized proteomic meth-ods to examine the array of proteins that are expressed in trisomic vs.euploid embryonic day (E)14.5 hearts via of two-dimensional proteingel electrophoresis, Delta 2D software analysis, mass spectrometryand MASCOT data analysis. Modifications of proteomic methods —

minimizing volumes, eliminating protein quantification steps, andoptimizing staining methods — were critical. Comparison of proteinsfrom single E14.5 hearts allowed identification of nine protein spots

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with significantly higher levels of protein in trisomic than euploidhearts, including myosin regulatory light chain 2 atrial isoform(MLC2a), reticulocalbin, and ezrin. With analysis of protein spotssignificantly underexpressed in E14.5 trisomic hearts, one significantprotein, MLC2v, the ventricular isoform, was identified. MLC2v is acritical component of chamber specification; overexpression couldresult in abnormal septation, although compensatory action byMLC2a may mitigate this effect. This work represents a novelapproach to evaluating the effects of dosage imbalance duringdevelopment and identified multiple proteins whose abnormalexpression levels may disrupt cardiogenesis to produce the patholo-gical conditions in trisomic embryos with cardiovascular defects.

doi:10.1016/j.ydbio.2011.05.647

Program/Abstract # 234Genomic approaches to understanding atrial septationAndrew Hoffmann, Joshua Bosman, Michael Herriges,Ivan MoskowitzUniversity of Chicago, Chicago, IL, USA

Atrial septation is a critical step in separating the systemic andpulmonary circulations in tetrapods and atrial septal defects areamong the most common forms of human congenital heart disease.The canonical view of atrial septation is based on intra-cardiacmorphogenetic events, however, recent studies highlight the criticalrole played by Hedgehog signaling in the second heart field. Here weaim to define the Hedgehog-mediated molecular networks requiredfor atrial septation in the developing mouse embryo using combinedgenomic approaches. We have developed and validated a micro-dissection procedure to isolate posterior second heart field (pSHF)tissue. To define Shh dependent transcripts, we have performedtranscriptional profiling of pSHFs inwildtype and Shhmutant embryosat E9.5. 146 up-regulated and 124 down-regulated transcripts havebeen identified, of which 40 have been validated by RT-PCR. Initialexpression analysis suggests 4 discrete domains of gene expression inthe pSHF: medial mesenchymal, ventral mesenchymal, lateral en-dodermal, and lateral mesothelial. We interpret these patterns withrespect to previous identified functions of the genes analyzed andpropose a testable model in which a lateral proliferating populationand a ventral-medial differentiating population of cells in the posteriorSHF are required for atrial septation. To complement the microarrayexpression data, we have developed an in-vivo ChIP-seq protocol toidentify direct targets of Hh signaling in the pSHF. Expressing the Flag-tagged Gli1 or Gli3 transcription factor in the SHF Mef2c lineage, ourpreliminaryGli:Flag-ChIP data show8-fold enrichment for a knownGlibinding region in the Ptch1 locus. Integrating our gene expression andGli-binding results will elucidate the Hh-dependent SHF molecularpathways required for atrial septation.

doi:10.1016/j.ydbio.2011.05.648

Program/Abstract # 235Mbc, active Rac1 and F-actin foci localize to points of cell contactin fusion-competent myoblasts, where they drive fusion withfounder cells and myotubesShruti Haralalkaa, Claude Sheltonb, Heather Cartwrightb, SusanAbmayrbaStowers Institute Developmental Biology, Kansas City, MO, USAbStowers Institute for Medical Research, Kansas City, MO, USA

Myoblast fusion in the Drosophila embryo initially occurs betweenfounder cells, which pattern the musculature, and fusion competent

myoblasts (FCMs). This precursor continues to fuse with additionalFCMs until the final myotube size is achieved. Cell surface proteinsSns and Kirre mediate recognition between these two cell types, andare critical in the FCMs and founder cells/developing myotubes,respectively. In contrast to this initial asymmetry, current models formyoblast fusion predict that the bipartite guanine nucleotideexchange factor Mbc and its target Rac1 function symmetrically inthe fusion process. Such models have also inferred that actin foci arealso symmetric at the fusion site. Our results demonstrate that thesite of fusion is quite asymmetric, however, with respect to theseproteins and the process of fusion. We have analyzed Mbc, activatedRac1 and F-actin using a combination of functional analysis and timelapse imaging in the embryo as well as protein localization in primarymyoblasts. These studies demonstrate, first, that Mbc is essential inthe FCMs but that the founder cells are capable of fusing with FCMs inits absence. Functional studies also show that activated Rac1 in theFCMs rescues the mbc loss of function phenotype, confirming that therole of Mbc is to activate Rac1. Our data further show that Mbc, activeRac1 and F-actin foci are highly enriched, if not exclusive, to the FCMsat their contact sites with founder cells and developing myotubes. Wehave confirmed the localization of F-actin during fusion by liveimaging in embryos. Of note, we also observe Mbc, active Rac1 and F-actin in Sns:Kirre associated projections that emanate from the FCMsand appear to push into the myotube.

doi:10.1016/j.ydbio.2011.05.649

Program/Abstract # 236Mapping and phenotypic characterization of the dead elvis (del)mutation in zebrafishEthan Carvera, Lauren Millevilleb, Michael Taylorc, Charles Lessmand

aUniv of Tennessee At Chattanooga Biological & Environmental Sciences,Chattanooga, TN, USAbUT Chattanooga, Chattanooga, TN, USAcSt. Jude Children's Research Center, Memphis, TN, USAdUniversity of Memphis, Memphis, TN, USA

During embryonic development, subsets of cells differentiate intodiscrete muscle tissues. This process forms tissues that allow theembryo to propel itself, contract the heart muscle to drive bloodthroughout the organism, and perform other functions necessary forsurvival. Our project is focused on a specific zebrafish mutant, deadelvis (del), which was discovered through a novel screeningmethodology in Dr. Lessman's laboratory at the University ofMemphis. The dead elvis (del) mutation manifests a non-motile,homozygous phenotype around 20 h after fertilization. The dead elvismutant has obvious myotome defects and a lack of sarcomereorganization. This project involves the genetic mapping and pheno-typic characterization of the dead elvis mutation. Using a wholegenome screen, we localized the mutation to LG9, and isolatedcandidate genes. Utilizing immunohistochemistry and confocalmicroscopy techniques, we have observed muscle formation andsarcomeric assemblage differences in the dead elvis mutant. Furtherstudy of this mutation may aid in the understanding of myotomedevelopment and lead to more insight into human neuromusculardisease conditions.

doi:10.1016/j.ydbio.2011.05.650

Program/Abstract # 237Elucidating the circadian-controlled gene xNocturnin's expressionand function in somitogenesisNicole Johnsona, Kristen Curranb

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