Congress Abstracts - Society for Developmental Biology

functions by the recruitment of additional targets as well as by slight variations in the small RNA sequences.
Program/Abstract # 34
Tetraspanin18 maintains Cadherin6B protein to antagonize cranial neural crest epithelial to mesenchymal transition
Laura S. Gammill, Corinne L. Fairchild, Joseph P. Conway (U Minnesota, USA)
Unlike their neurepithelial neighbors in the neural tube, neural crest cells undergo an epithelial to mesenchymal transition (EMT) and
migrate. We have defined novel post-translational control of cranial neural crest EMT. Premigratory cranial neural crest cells express
the transmembrane scaffolding protein tetraspanin18 (Tspan18), which is downregulated prior to migration. Sustained Tspan18
expression prevents cranial neural crest migration and maintains epithelial Cadherin6B (Cad6B) protein despite temporally normal
downregulation of Cad6B mRNA. This suggests that Tspan18 antagonizes EMT by post-translationally maintaining Cad6B protein to
promote epithelial cell adhesion. In support of this, Tspan18 knockdown leads to premature loss of Cad6B protein from the neural
folds. Nevertheless, Tspan18 knockdown is insufficient for precocious migration, at least in part because other steps in EMT take
place on schedule. At the onset of EMT, Tspan18 transcriptional repression is independent of the EMT transcription factor Snail-2, but
downstream of FoxD3, which is both necessary and sufficient for Tspan18 mRNA downregulation and neural crest migration.
Altogether, our results reveal Tspan18-dependent maintenance of Cad6B protein in epithelial cranial neural crest cells that is relieved
by FoxD3-dependent downregulation of Tspan18 at the onset of EMT. Thus, in a pathway parallel to Snail-2 transcriptional repression
of Cad6B, FoxD3/Tspan18 define a new transcriptional/post-translational input into cranial neural crest EMT that offers mechanistic
insight into the timing of neural crest emigration as well as the poorly understood anti-metastatic activity of some tetraspanins.
Supported by NIH F31GM087951 and a U of MN Grant in Aid.
Program/Abstract # 35
The tissue-specific lncRNA Fendrr is an essential regulator of heart and body wall development in the mouse
Phillip Grote, Lars Wittler (Max Plunck Inst for Molec. Genetics, Germany); David Hendrix (MIT, USA); Frederic Koch, Bernhard
Herrmann (MPI Molec Genet., Germany)
Long non-coding RNAs (lncRNAs) have been shown to influence gene expression by modulating histone modifications and affecting
chromatin accessibility. This function involves binding of lncRNAs to the histone modifying Polycomb-repressive complex 2 (PRC2)
or Trithorax group (TrxG/MLL) proteins, implicating lncRNAs in lineage commitment, cellular differentiation and embryonic
development. We identified Fendrr as a tissue specific lncRNA, which is transiently expressed in the nascent lateral mesoderm, giving
rise to the heart and body wall. Inactivation of Fendrr by gene targeting resulted in embryonic death after stage E13.5 due to
malfunctioning of the heart, and in rupture of the ventral body wall. The molecular analysis showed that transcription factors
controlling lateral plate or cardiac mesoderm differentiation are up-regulated in Fendrr mutant embryos. This was accompanied by an
increase in the activating histone H3 Lys4 tri-methylation (H3K4me3) mark either alone or in combination with a decrease of the
repressive H3 Lys27 tri-methylation (H3K27me3) mark at their promoters, indicating deregulated PRC2 and TrxG activity at a subset
of control genes. Moreover, PRC2 occupancy was decreased at the regulatory regions showing reduced H3K27me3 levels. Fendrr
binds to both histone modifying complexes in vivo and to dsDNA derived from target promoters in vitro. Our data identifies a
lncRNA that plays an essential role in balancing activating and repressive histone marks at target promoters and is involved in
regulatory networks controlling the development of lateral mesoderm derivatives.
Program/Abstract # 36
Identification of a non-coding RNA as a negative regulator of JNK signaling during Drosophila dorsal closure
L. Daniel Ríos-Barrera, Juan R. Riesgo-Escovar (UNAM, Mexico)
Dorsal closure is one of the last steps in Drosophila embryogenesis, whereby the lateral epidermis stretches dorsally to completely
wrap the embryo. We have identified a gene, acal, whose mutations result in dorsal closure defects. acal has low protein coding
potential and its transcript is enriched in nuclear preparations. Strikingly, acal is processed into fragments in the range of 40 to 100
nucleotides. Hence, we propose that acal is a non-coding RNA. During dorsal closure, acal is expressed mainly in the central nervous
system and in the lateral epidermis. Rescue of acal in the lateral epidermis is sufficient to suppress dorsal closure defects. To
determine the role of acal in dorsal closure, we analyzed activation of the JNK pathway, the dorsal closure trigger, in acal mutants. By
means of a JNK activity reporter (puc-lacZ), we found that acal mutants present ectopic activation of JNK signaling. Consistently,
reducing the JNK gene dosage partially rescues the acal mutant phenotype. These results show that acal is a negative regulator of JNK
signaling during dorsal closure. The expression pattern of acal during dorsal closure is very similar to that of raw, a negative regulator
of JNK signaling of unknown molecular function. In raw mutants, acal epidermal expression is strongly reduced, suggesting that acal
lies downstream of raw. To support these results, we analyzed thoracic closure, a process analogous to dorsal closure occurring during
metamorphosis. Ectopic expression of acal or raw alone has no effect on thorax closure; however, co-expression of both genes
impairs thoracic closure. Altogether, our results show that raw acts at least partially through acal to regulate dorsal closure by
antagonizing JNK signaling.
Program/Abstract # 37
Regulation of histone mRNA by PIWI homologs in planarian stem cells
Labib Rouhana, Jennifer Weiss, Phillip Newmark (U IL at Urbana-Champaign, USA)
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