Abstracts - Society for Developmental Biology

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embryos showed normal onset of the PrE program but exhibited a defect in its restriction phase, where lineage bias is
acquired. Sustained exogenous FGF4 failed to rescue the mutant phenotype. Instead, depending on concentration, we noted
no effect, or conversion of all ICM cells to GATA6-positive PrE. This suggested that paracrine signaling and local
availability of FGF results in a salt-and-pepper distribution of lineage-biased cells. Our data also revealed that XEN
(eXtraembryonic Endoderm) cells could be derived from Fgf4 mutant embryos in which PrE had been restored, showing
that FGF signaling is essential for PrE lineage choice but dispensable for XEN cell maintenance.
Program/Abstract # 447
A putative role for Yap1 phosphorylation during trophoblast differentiation in the laboratory opossum,
Monodelphis domestica
Safa, Nadia, Oberlin College, Oberlin, OH, United States
A pluriblast-trophoblast differentiation process in the unilaminar blastocyst of the laboratory opossum, Monodelphis
domestica, commences on the fifth day of development, shortly after the blastomeres have adhered to the zona pellucida.
This process is associated with the mutually exclusive expression of Oct4 and Cdx2 proteins in the pluriblast and
trophoblast, respectively. Yap1 expression mirrors this pattern, being confined to the cytoplasm in the pluriblast cells but
only in the nuclei of trophoblast cells. This suggests that, as in the mouse embryo, Yap1 is a transcription co-activator of
the trophoblast-specifying protein Cdx2. Nuclear entry by Yap1 can occur when the protein is in its unphosphorylated
state, permitting it to activate Cdx2. Conversely, phosphorylated Yap1 (pYap1) is unable to enter the nucleus, preventing it
from carrying out its function. We tested the hypotheses that pYap1 expression in opossum blastocysts a) is confined to the
cytoplasm of opossum pluriblast, and b) is not be observed in the trophoblast cells. Our results indicate that, as expected,
pYap1 is undetectable in the pluriblast nuclei. However, pYap1 is reliably detected in trophoblast cells, specifically in a
small restricted domain within the trophoblast nuclei. This suggests the complexity of Yap1 protein interactions, namely
that Yap1 may gain nuclear entry irrespective of its phosphorylation status.
Program/Abstract # 448
O-fucosylation regulates zebrafish dorsal-ventral patterning by inhibiting BMP signaling
Feng, Lei; Jiang, Hao; Marlow, Florence; Wu, Peng, Albert Einstein College of Medicine, Bronx, United States
Glycosylation, the modification of proteins with sugars, plays very important roles in all biological processes. O-
fucosylation, which adds fucose to the serines or threonines of a wide variety of cell surface and secreted proteins, impacts
nearly every stage of vertebrate development. However, early embryonic lethal phenotypes of homozygous mutants
disrupting O-fucosylation prevent access to its contribution to later developmental processes. Therefore, our understanding
of O-fucosylation function during early development is still sketchy. Many critical questions, including which signaling
pathways and how O-fucosylation modulates their activity remain unclear. To address these questions we have developed a
hyper-O-fucosylation model by overexpressing the endoplasmic reticulum GDP-Fucose transporter, slc35c2. Embryos
treated with slc35c2 showed clear dorsalization phenotypes. When combined with excess GDP-fucose, treated embryos
showed significant increases in the severity and penetrance of the dorsalization phenotypes, while GDP-fucose alone
caused no phenotypes. The balance between BMP signaling and its antagonists are known to pattern the dorsoventral axis
of zebrafish embryos. We observed that inhibition of BMP signaling underlies dorsalization caused by excess O-
fucosylation. Diminished BMP signaling was evident in lessened Phospho-Smad1/5 level and reduced expression of
ventral fates regulators, including transcription factors and BMP ligands from the earliest stages examined. Reciprocally,
BMP antagonist expression was expanded. Furthermore, excess O-fucosylation induced dorsalization could be suppressed
by overexpression of BMP7a and BMP2b ligands. Together these data indicate O-fucosylation regulates dorsal-ventral
patterning in zebrafish by modulating BMP signaling.
Program/Abstract # 449
Role of acyl Co-A synthases in Drosophila embryonic development
Johri, Shaili; Letsou, Anthea, University of Utah, Salt Lake City, United States
Gastrulation is one of the earliest observable morphological events which transform a blastula into a multilayered embryo
with three germ layers. A key morphogenetic event in Drosophila gastrulation is ventral furrow formation and it leads to
the internalization of mesodermal precursors. In order for the ventral furrow to form, cells destined to form the mesoderm
constrict, shorten, flatten and then shift towards the interior of the embryo. Ventral furrow formation marks the beginning
of gastrulation, and the cellular movements as well as the molecular players involved in this process are conserved across
species. While genetic analysis has revealed the genes involved in the specification of mesodermal cells, many of the
effector molecules that mediate cytoskeletal rearrangements during ventral furrow formation remain unknown. A unique
opportunity to understand this patterning/effector gene interface is offered by bubblegum (bgm), an acyl Co-A synthase