Abstracts - Society for Developmental Biology

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Program/Abstract # 107
Shroom3-dependent apical constriction requires an association with the adherens junctions through p120 catenin
Plageman, Timothy F.; Lang, Richard, Cincinnati Children's Hospital, Cincinnati, United States
During eye morphogenesis, the lens placodal cells elongate and adopt a wedge or conical shape in a process termed apical
constriction (AC). This cell shape change drives lens pit invagination and requires the cytoskeletal protein Shroom3.
Shroom3 activity is dependent on its interaction with Rock1, which stimulates the activation and contraction of the apically
positioned actomyosin network. It has been shown in other models of AC that the contraction of actomyosin filaments
generates force on the apical junctions pulling them toward the middle of the cell and effectively reducing the apical
circumference. In lens placodal cells, we have similarly observed apically positioned myosin-containing filaments
associated with adherens junctions at the point of deformation. It is currently unknown how the contractile actomyosin
network in the lens placode is associated with the apical junctions and Shroom3-dependent AC machinery. To determine if
Shroom3 genetically interacts with essential components of adherens junctions, Shroom3 targeted mice were bred with
those containing conditional alleles of E-cadherin, N-cadherin, b-catenin, and p120 catenin (p120). Surprisingly, we found
that Shroom3/p120 double heterozygotes displayed severe neural tube and eye morphogenetic defects at high penetrance
suggesting that Shroom3 and p120 may be functioning together during epithelial morphogenesis. When conditionally
removed from the lens pit we observed that p120 and Shroom3 deficient lens pits are similarly misshapen and that like
Shroom3, p120 is required for lens pit AC. In addition, we found that p120 is required for Shroom3 induced AC in
cultured cells. Together, these data suggest a potential interaction between the Shroom3-dependent AC complex and the
apical junctions through p120 catenin.
Program/Abstract # 108
An essential role for claudins in neural tube closure in chick
Baumholtz, Amanda; Collins, Michelle; Simard, Annie; Ryan, Aimee (McGill University, Montreal, Canada)
Neurulation is a developmental process that results in the rolling up of a flat sheet of epithelial cells into an elongated tube.
While the process of neurulation has been extensively studied, the genes that regulate the morphogenesis of the neural tube
remain poorly understood. We have completed expression analyses of 17 members of the claudin family of tight junction
proteins during neurulation in chick embryos. At neurulation, claudin family members exhibited three expression patterns:
uniform expression across the ectoderm, reduced expression in the neural ectoderm and enriched expression in the neural
ectoderm. To determine if claudins play a role in neural tube closure, we used the C-terminal domain of Clostridium
perfringens enterotoxin (C-CPE) to knock down claudins in the ectoderm of chick embryos at the neural plate stage.
Embryos were cultured with bacterially purified C-CPE using the ex ovo cornish pasty method. After 20 hours, GSTtreated
embryos developed normally while C-CPE-treated embryos had an open neural tube, a shortened anteroposterior
(AP) axis and abnormally shaped somites. Neural tube defects (NTDs) were classified according to the level of the
opening along the AP axis which corresponds to the human phenotype: 50% completely open (craniorachischisis), 25%
open at anterior end (anencephaly), and 25% open at posterior end (spina bifida). Preliminary in situ hybridization analysis
of the GST-C-CPE-treated embryos revealed that genes expressed in the neural and non-neural ectoderm have a normal
expression pattern. These data suggest that claudins are required for neural tube closure and not for the initial
differentiation of cells in the neural ectoderm.
Program/Abstract # 109
Cofilin1 and PTEN are involved in two cell autonomous processes required for cephalic neural tube closure.
Grego-Bessa, Joaquim; Anderson, Kathryn, Memorial Sloan Kettering Cancer Center, New York, United States
Closure of the mouse neural tube (NTC) is regulated by different genes along the anterior- posterior body axis. For
example, Planar Cell Polarity mutants show NTC defects in the trunk, excluding the head; in contrast, Shroom mutants
show NTC defects exclusively in the head. In this work we define new players that regulate closure of the cephalic neural
tube. Cofilin 1 (Cfl1) is an actin binding protein that regulates actin dynamics by severing actin filaments. Strong Cfl1
mutants die at midgestation with prominent exencephaly. We find that Cfl1 mutants have dramatic defects in apical-basal
polarity where a single cell can have two apical domains at opposite poles of the cell, as shown by ectopic localization of
apical markers. As vesicular trafficking is required for cell polarity, we analyzed different vesicular markers in the neural
plate. In WT they are localized along the apical-basal axis of neuroblasts, but in Cfl1 mutants they appear to accumulate to
the apical surface, suggesting that Cfl1might regulate apical-basal polarity and NTC by regulating vesicular trafficking.
The tumor suppressor gene PTEN can regulate proliferation, cell size, apoptosis and cell polarity. We found that
conditional deletion of PTEN in the epiblast is lethal at E9.5 and mutants fail to close the cephalic neural tube. In this
tissue, loss of PTEN does not affect proliferation, cell size or cell death, but instead prevents elongation of neuroblasts and