Congress Abstracts - Society for Developmental Biology

also generated several of such transgenic lines in X. laevis. Remarkably, the expression patterns of dGFP in X. laevis in general
resemble those in X. tropicalis. To further explore the potential usage of these reporter lines, we make use of the tailored-TALENs
(Transcription activator-like endonucleases) to direct gene disruption of few known modulators of the Wnt/beta-catenin pathway on
the transgenic embryos and analysing the gene knockdown effects on the reporter expression. Our preliminary results showed that this
combination approach holds a great potential for further investigating functions and uncovering new regulators of the Wnt/betacatenin
signaling.
Program/Abstract # 145
Ets-1 is an Essential Regulatory Factor of Neural Crest Formation in Xenopus
Geary, Lauren (Northwestern University, USA)
Neural crest cells are a hallmark of vertebrate embryos, and an excellent system in which to address questions about how stem cell
attributes are acquired and how cell behavior is integrated with changes in cell fate. Neural crest cells arise at the neural plate border in
regions of intermediate BMP signaling, and Wnt signals are essential for their induction. FGF signals have also been implicated in
neural crest induction, although the precise contributions FGF signals make to neural crest formation has been controversial. A full
understanding of the upstream regulation of this important cell population requires better insight into the respective roles of these
signaling pathways. Members of the ETS family of transcription factors are common downstream mediators of receptor tyrosine
kinases such as the FGF receptor. A number of ETS proteins have been implicated in neural crest induction, migration, and
differentiation, yet when they are active and how they are regulated remains elusive. Here, we show that in Xenopus, the founding
ETS family member Ets-1 is expressed in neural crest forming regions of the ectoderm, and that its expression is maintained in the
neural crest through migratory stages. Ets-1 is an essential component of the neural crest gene regulatory network (NC-GRN) as
morpholino-mediated depletion of this factor disrupts the expression of neural crest specifier genes. We present evidence on the role
and regulation of Ets-1 in the formation and subsequent development of the neural crest.
Program/Abstract # 146
Tgfß3 signals through Twist1 and then Snail1 to down regulate E-cadherin expression during epithelial-mesenchymal
transition (EMT) in the palate
Svoboda, Kathy K. (Texas A&M Univ Baylor College of Dentistry, USA); Yu, Wenli (University of California-San Francisco, USA);
Ruest, L-Bruno (Texas A&M Baylor College of Dentistry, Dallas, USA)
Palatal fusion is a tightly controlled process which comprises multiple cellular events downstream of cell surface signaling, including
cell movement and differentiation. Midline epithelial seam (MES) degradation is essential to palatal fusion. One feature of MES
degradation is the down regulation of E-cadherin. Snail1 is expressed in the MES and is a known repressor of E-cadherin. In this
study, we asked if Snail1 was necessary for palatal fusion. We also determined a possible mechanism regulating the expression of the
Snail1 gene in palatal shelves. Whole mount in situ hybridization combined with organ cultures of mouse palatal shelves, with ChIP
and luciferase assays in cultured cells and RT-PCR experiments were used to study transcriptional regulation of E-cadherin. Mouse
palatal explants treated with Snail 1 siRNA did not degrade the MES and E-cadherin was not repressed leading to failure of palatal
fusion. We had previously shown that transforming growth factor beta 3 (Tgfb3) activated Twist1 expression in the MES cells before
degradation. In this study, Tfgβ3 regulated Snail1 mRNA, as Snail1 expression decreased in response to Tgfb3 neutralizing antibody
and a PI3K inhibitor (LY294002). Snail1, Twist1 and E2A genes were expressed in the E13.5 mouse palate in overlapping expression
patterns. Luciferase assays were used to determine that Twist1, in collaboration with E2A transcription factors, regulated the
expression of Snail1. Twist1/E47 dimers bond the Snail1 promoter to activate expression. Without E47, Twist1 repressed Snail1
expression. These results support the hypothesis that Tgfβ3 signals through Twist1 and then Snail1 to down regulate E-cadherin
expression during palatal fusion.
Program/Abstract # 147
The Transcriptional Regulation of Muscle Development in Drosophila melanogaster
Brunetti, Tonya; Duong, Sandy; Cripps, Richard (University of New Mexico, USA)
Muscle development in Drosophila is beneficial due to the diverse and unique set of muscle types in the thorax. Using specific
muscle type enhancer elements and a reverse genetic screen has allowed us to recognize regulators of muscle development. We have
identified new roles for two transcription factors that have human orthologs and function in either the regulation of muscle identity or
in the proper fusion of myoblasts. These two transcription factors are extradenticle (exd) and Myocyte enhancer factor 2 (MEF2).
Exd has been shown to control muscle identity by working in concert with homothorax. The two genes are expressed in all muscle
types except the tergal depressor of the trochanter in the thorax. The absence of either gene results in a fiber type switch from fibular
to tubular. Further investigation has shown these genes bind to Actin88F, a structural gene found in fibular muscles. The binding of
these genes results in proper expression of structural genes which allows for correct muscle identity. Without these genes, the muscles
lose their identity and begin to atrophy. In contrast, Mef2 has been shown to regulate muscle formation. The absence of Mef2 results
in the lack of muscle formation, ultimately leading to pupae death. Upon the analysis of the fusion gene, singles bar (sing), RT-PCR
revealed MEF2 as a potential regulator of sing expression. Knockdowns of sing result in lethality due to the inability for myoblasts to
fuse together to form syncytial muscle fibers. This finding has thus provided a novel function for MEF2 in myoblast fusion. Thus,
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