Abstracts - Society for Developmental Biology

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developed, we show that application of recombinant PTHrP, Egf-family ligands, or Wnt3A proteins stimulated branching
of embryonic mammary glands suggesting that these pathways may cooperatively mediate the effects of Eda. Moreover,
we show that in contrast to wild-type male mice, ductal growth proceeded in K14-Eda males similarly to transgenic
females.
Program/Abstract # 122
Twisted gastrulation, an extracellular BMP binding protein, is required for postnatal mammary gland
morphogenesis
Forsman, Cynthia, University of Minnesota Genetics, Minneapolis, United States
The role bone morphogenetic proteins (BMPs) play and how they are regulated in the postnatal mammary gland (MG)
remains virtually unknown. It has been established that BMPs are involved in embryonic MG development and can be
dysregulated in breast cancer. This study examines the role of Twisted gastrulation (TWSG1), an extracellular BMP
binding protein that can modulate BMP signaling, during postnatal MG development. LacZ staining demonstrates that
TWSG1 is expressed in the myoepithelium of the postnantal MG but immunolocalization studies show TWSG1 in both the
myoepithelium and the epithelium suggesting a role for TWSG1 in epithelial/stromal communication. Global deletion of
Twsg1 leads to a delayin ductal elongation, hyperplastic terminal end buds, occluded lumens and cell shedding.
pSMAD1/5/8 level and the expression of BMP target genes (Msx2, Gata-3) are reduced, consistent with a decrease in
BMP signaling. Apoptosis of excess body cells is required for lumen formation and in the Twsg1-/- MG apoptosis is
reduced which may contribute to occluded lumens seen in these MG. Furthermore, shed cells and some cells within the
luminal compartment are K14-positive, while normally K14-positive cells are restricted to the myoepithelial layer
suggesting that regulation of BMP signaling by TWSG1 is required for myoepithelial compartmentalization. Altogether,
these data show that TWSG1 facilitates BMP signaling and plays a role in ductal morphogenesis in the postnatal MG.
Program/Abstract # 123
Planar cell polarity proteins differentially regulate ECM organization during zebrafish gastrulation
Jessen, Jason; Williams, Blairanne; Mundell, Nathan, Vanderbilt University Medical Center Medicine, Nashville, United
States
During zebrafish gastrulation, planar cell polarity (PCP) is defined as the elongation and mediolateral alignment of cells
engaged in polarized behaviors including collective migration. A decade ago it was shown that homologs of proteins
regulating PCP in fly cuticular structures also control PCP in gastrula cells. Loss of PCP gene function in mutants such as
trilobite/vang-like 2 (vangl2) produces a phenotype characterized by shortened and broadened embryonic body axes.
While it is thought that disrupted membrane protrusive activity underlies the PCP defect in vangl2 mutants, the
establishment of PCP must be coordinated with, and perhaps also regulates, dynamic changes in extracellular matrix
(ECM) organization. Previously our lab demonstrated that membrane type-1 matrix metalloproteinase (Mmp14) is required
for PCP exhibiting a strong genetic interaction with knypek/glypican4, a Wnt co-receptor necessary for gastrulation cell
movements. Subsequently we showed that a fibronectin- and laminin-containing ECM network develops coincidently with
the onset of PCP. We have now demonstrated that Vangl2 regulates the endocytosis and cell surface proteolytic activity of
Mmp14. Furthermore, our data show that Mmp14 acts as a downstream effector of Vangl2 signaling during gastrulation.
Similar to vangl2 mutants, wild-type embryos injected with prickle antisense morpholinos have reduced fibronectin. By
contrast, glypican4 and frizzled7a/7b mutant embryos exhibit increased fibronectin fibrillogenesis without an increase in
fibronectin protein levels. These data suggest that while Vangl2/Prickle affect proteolysis of ECM substrates,
Frizzled/Dishevelled signaling likely influences ECM organization by impacting intercellular adhesion.
Program/Abstract # 124
Dynamin is required for the maintenance of EVL integrity and the progression of epiboly
Lepage, Stephanie; Bruce, Ashley, Univ of Toronto, Canada
Epiboly, the first morphogenetic cell movement that occurs in the zebrafish embryo, is the process by which the
blastoderm thins and spreads to engulf the yolk cell. This process requires the concerted actions of the deep cells, which
make up the embryo proper, and the two extra-embryonic tissues, the enveloping layer (EVL) and yolk syncytial layer
(YSL). One mechanism predicted to contribute to the progression of epiboly is the endocytic removal of yolk cell
membrane, just ahead of the advancing blastoderm, in the region of the YSL. Using a drug-based approach, we
demonstrate that marginal endocytosis occurs in a Dynamin-dependent and Clathrin-mediated manner and that inhibition
of either Dynamin or Clathrin results in a severe epiboly delay. In contrast, localized expression of dominant-negative
(DN)-Dynamin 2 in the yolk cell reduced marginal endocytosis, but epiboly still progressed normally. This suggests that
endocytic removal of yolk cell membrane is dispensable for the successful progression and completion of epiboly. Instead,