also regulates Twist. Ppa binds Twists highly conserved WR domainand promotes its instability. Our findings suggest that the ubiquitin–proteasome system modulates the protein expression levels ofmultiple structurally distinct EMT regulatory factors, including Twist,Snail, Slug, and Sip1, through the actions of a common E3 ligase. TheWR domain can mediate additional protein–protein interactions thatimpact Twist function during neural crest development, distinct fromits effect on Twist stability. Together our findings provide novelinsights into the function of a key regulator of both early embryonicdevelopment and tumor progression.

doi:10.1016/j.ydbio.2011.05.420

Program/Abstract #459The role of Miz-1 in EMT and migration in the neural crestLaura K. Kerosuo, Marianne Bronner-FraserCalifornia Institute of Technology Biology, Pasadena, CA, USA

The neural crest cells undergo Epithelial to Mesenchymaltransition (EMT) as they delaminate from the neural tube andmigrate to various target destinations in the developing embryo. Byreactivation of the developmental programs due to oncogenicmisregulation of the transcriptional control mechanisms, EMT allowsthe release of mesenchymal-like cells from the parent epithelialtissue and thus leads to metastatis formation. Despite its crucialcontribution to tumor progression the gene regulatory networkbehind EMT is still relatively poorly understood. Ex ovo manipulationof the chicken embryo enables targeted in vivo knockdown of genesand real time analysis of the downstream effects. The Myc interactingzinc finger protein 1 (Miz-1/ZBTB17) is a transcription factordownstream of the TGF-b signaling pathway that promotes cell cyclearrest, epidermal stem cell adhesion and inhibits the recurrence oflymphoma formation. C-Myc directly binds to Miz-1 and repressesthe expression of its downstream target genes. Miz-1 and c-Myc areboth expressed in the delaminating and migrating chicken neuralcrest. Here, we have studied the role of Miz-1 in the regulation of theneural crest. By using the Miz-1 Morpholino, in situ hybridization andQ-PCR our preliminary data shows a significant change in theexpression pattern of several EMT and migration related genes.

doi:10.1016/j.ydbio.2011.05.421

Program/Abstract #460Transcription factors Gata4 and Gata6 play compensatory roles inpancreas developmentShouhong Xuana, Matthew Boroka, Stephen Duncanb, Lori SusselaaColumbia University, New York, NY, USAbMedical College of Wisconsin, Milwaukee, WI, USA

Gata4 and Gata6 are zinc finger transcription factors that bind to acommon DNA motif (A/T)GATA(A/G). Gata4 and Gata6 are expressedin several endoderm and mesoderm derived organs, including theliver, pancreas and heart, where they have been shown to havedistinct and overlapping functions. Gata4 and Gata6 null mice dieprior to pancreas formation, precluding the analysis of their functionsin pancreas development. To overcome this limitation, we generatedpancreas specific knock-outs of Gata4 and Gata6 using the Pdx1:Cremouse. Pancreas-specific deletion of either Gata4 or Gata6 individu-ally did not reveal obvious defects in pancreas development. To testwhether Gata4 and Gata6 may compensate for each other duringpancreas development, we generated Pdx1:Cre;Gata4fl/fl;Gata6fl/fl(G4/G6DKO) mice. The G4/G6DKO pups are hyperglycemic and themajority of mutant animals die shortly after birth. At P0, histological

and immunostaining studies demonstrated that pancreas develop-ment is severely affected, with very little identifiable exocrine andendocrine tissues. Analysis of the G4/G6DKO at e9.5 revealed thenormal induction of the pancreatic buds; however, as developmentproceeds, the pancreas displays retarded growth and reducedbranching. Molecularly, there was also reduced expression ofpancreatic progenitor markers such as Pdx1, Ptf1a, Sox9 and Nkx6.1.By e16.5, pancreas tissue in G4/G6DKO embryos is undetectable. Weare continuing to phenotypically and molecularly characterize theG4/G6DKO mice to identify the downstream developmental path-ways in the pancreas that are affected by the combined loss of Gata4and Gata6.

doi:10.1016/j.ydbio.2011.05.422

Program/Abstract # 461Dynamic expression pattern of Tbx2 and Tbx3 in the developingand adult mouse pancreasSalma Beguma, Virginia PapaioannoubaColumbia University Genetics & Development, New York, NY, USAbColumbia University, New York, NY, USA

Tbx2 and Tbx3 are closely related members of the T-box family oftranscription factors that are important regulators during normaldevelopment as well as major contributors to human developmentalsyndromes when mutated. Although there is evidence for theinvolvement of Tbx2 and Tbx3 in pancreatic cancer, so far there areno reports characterizing the expression pattern of these genes in thepancreas. In this study, we examined spatial and temporal expressionof Tbx2 and Tbx3 in mouse pancreas during development and inadult using in situ hybridization and immunohistochemistry. Ourresults show that Tbx2 and Tbx3 are expressed in the pancreaticmesenchyme throughout development beginning at embryonic day9.5. In addition, Tbx2 is expressed in epithelial-derived endocrine andductal cells during late fetal stages, during postnatal developmentand in adult pancreas. Tbx2 is also expressed in pancreaticvasculature during development. In contrast, Tbx3 is expressed inexocrine tissue in the postnatal and adult pancreas. Our resultsfurther demonstrate that Tbx2 and Tbx3 are expressed in endocrineand exocrine cell lines respectively. These dynamic changes in theexpression pattern of these transcription factors lay the foundationfor investigation of potential roles in pancreas development.

doi:10.1016/j.ydbio.2011.05.423

Program/Abstract # 462The LIM co-factor Ldb1 is enriched in pancreatic islet cells andrequired for proper cell development and functionChad Huntera, Tsadok Cohenb, Benjamin Edigerc, Crystal Wilcoxc,Shilpy Dixita, Heiner Westphald, Roland Steina, Catherine MaycaVanderbilt University Medical Center, Nashville, TN, USAbEunice Kennedy Shriver National Institute of Child Health and HumanDevelopment, Bethesda, MD, USAcChildren's Hospital of Philadelphia, Philadelphia, PA, USAdKennedy Shriver National Institute of Child Health and HumanDevelopment, Bethesda, MD, USA

The LIM-Homeodomain (HD) and LIM-only (Lmo) transcriptionalregulators play important roles in formation of many tissues andorgans. We have shown that Isl1 is the principal LIM-HD proteinexpressed in the endocrine pancreas during development and inadults. Removal of Isl1 at the onset of secondary transition in Pdx1-Crelate;Isl1Fl/Fl mice during development resulted in a reduction of

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