Abstracts - Society for Developmental Biology

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cytoskeletal dynamics and cell migration. In the mouse, tissue-specific gene targeting experiments have shown that p120-
ctn may act through different mechanisms to promote cell-cell adhesion or cell migration indifferent cell types. In the
mouse deletion of p120-ctn is embryonic lethal. We are characterizing the phenotypes of p120-ctn mutant embryos to
determine a possible mechanism linking signaling and migration during early morphogenesis of the embryo. Embryos
lacking p120-ctn show morphogenetic defects including axial duplication and defects in mesoderm migration. The
production of mesoderm cells at the correct position in the embryo depends on the earlier movement of Anterior Visceral
Endoderm (AVE) cells, and we observe that AVE migration is abnormal in p120-ctn null embryos. Currently we are
analyzing changes in cell behavior of the Hex-GFP expressing AVE cells using time-lapse imaging in early embryos. In
addition we are analyzing whether these defects are associated with changes in E-cadherin. To determine the specific roles
of p120-ctn in the later embryo we ablated the gene specifically in the epiblast and we are characterizing that phenotype.
Our findings will define the functions of p120-ctn in normal development and will contribute to understand its roles in
diverse types of cancer cells.
Program/Abstract # 128
The polarity complex Par6b/Par3 is required for the normal pattern and function of cadherins in ectoderm cells
Wang, Sha; Cha, Sang-wook; Wylie, Christopher Cincinnati Children's Hospital Med Center, Cincinnati, United States)
The Par (partitioning defective) proteins Par6b and Par3 are expressed in Xenopus ectoderm. Here we show that the Par6b/
Par3 complex is required for the normal pattern and function of cadherins expressed by the ectoderm cells. Depletion of
Par6b in the non-neural ectoderm (the presumptive epidermis) causes a loss of E-cadherin. Cell-cell adhesion is retained at
first due to the continued expression of C-cadherin. Embryos start to shed epidermis around stage 32 when epidermal C-
cadherin is switched off. The neural ectoderm is also affected by Par6b depletion, which causes disruption of N-cadherin
expression at the cell surface and failure of neural fold closure. Depletion of Par3 shows similar effects as Par6b
knockdown, suggesting that Par6b and Par3 regulate cadherins as one functional complex or in the same pathway.
Expression of the apical marker Crumb3 and the baso-lateral marker Lgl2 suggests that Par6b depletion causes a change of
cell polarity leading to Crumb3 being stabilized all around the membrane of the non-neural ectoderm cells, whilst Lgl2
level is reduced. This may explain the loss of baso-laterally expressed E-cadherin. In addition, the tight junctions that
structurally define the apical-basolateral border are also reduced by depletion of Par6b. These data together show that
cadherins are under the control of the Par6b/Par3 complex, and that this complex controls the boundary between apical and
baso-lateral membrane in the early Xenopus ectoderm.
Program/Abstract # 129
Claudins are required for ureteric bud branching during kidney morphogenesis
Khairallah, Halim; El Andalousi, Jasmine; Ryan, Aimee; Gupta, Indra (McGill, Monntreal, Canada)
The claudin family of integral tight junction proteins has documented roles in tissue and organ morphogenesis, including
tubule and lumen formation of epithelial cell layers. In the adult mouse kidney, claudin family members are expressed
along the nephron and determine the specific paracellulartransport properties of each nephron segment. The function of
claudin proteins during kidney morphogenesis remains unclear. During kidney development, the ureteric bud emerges from
the nephric duct and undergoes branching morphogenesis: the ureteric bud elongates and divides in a series of repeated
bifurcations at the ureteric bud tips which ultimately give rise to the collecting ducts of the adult kidney. We have shown
that claudin-3 is expressed in the nephric duct and ureteric bud and promotes tubulogenesis in vitro. Based on our in vitro
studies, we hypothesize that claudins are required for ureteric bud branching. Using RT-PCR and in situ hybridization
analysis we found that 15 claudins are expressed at critical time points during mouse kidney development. Removal of
multiple claudins was performed by growing mouse embryonic kidney explants in the presence of the C-terminus of
Clostridium perfringens enterotoxin (C-CPE), which is known to bind to specific claudins and remove them from tight
junctions. Explants treated with C-CPE demonstrated a decrease in ureteric bud tip number and an increase in ureteric bud
stalk length compared to controls. We have targeted individual claudins using morpholinos and shown that knockdown of
claudin-3 decreases ureteric bud branching. In conclusion, our data suggest that claudins have a role in ureteric bud
branching during kidney morphogenesis.
Program/Abstract # 130
MAPK pathway is required for branch point determination
Kuure, Satu; Ihermann, Anneliis; Lume, Maria (University of Helsinki, Helsinki, Finland); Charron, Jean (Université
Laval, Quebec, Canada); Saarma, Mart (University of Helsinki, Helsinki, Finland); Costantini, Frank (Columbia
University Medical Center, New York, United States)