Abstracts - Society for Developmental Biology

121
Misregulation of molecular pathways controlling the epithelial-to-mesenchymal transition (EMT) underlying cranial neural
crest emigration, including adherens junction disassembly, may adversely affect neural crest development and result in
craniofacial defects. Cranial neural crest cells undergo EMT en masse to acquire motility, subsequently migrating
throughout the head and differentiating into a diverse range of cell types. In chick midbrain premigratory neural crest cells,
N-Cadherin (N-Cad) and Cadherin6B (Cad6B) proteins are down regulated prior toEMT, with their turnover coordinated
independently of transcriptional repression. We hypothesize that proteolytic processing depletes cadherin levels to
facilitate neural crest EMT. We have verified proteolytic cleavage of Cad6B and N-cad in vivo at stages immediately
following EMT by immunoblotting of midbrain lysates. To identify the protease(s) responsible for this cleavage, we have
co-expressed relevant candidate metalloproteinases observed in the chick midbrain with Cad6B or N-cad in vitro and have
identified members of the A Disintegrin and Metalloproteinase (ADAM) family to be important for cadherinc leavage. We
will now perform over expression and knock-down assays in vivo to confirm these in vitro results and to assess subsequent
effects on cadherin localization and neural crest cell EMT and migration. Collectively, our work will facilitate a better
understanding of the molecular mechanisms underscoring normal developmental and disease-related EMTs.
Program/Abstract # 366
Regulation of Slit-Robo signaling by Comm-family members in insects
Seeger, Mark, Columbus, United States; Carver, Laura; Jowdy, Casey (Columbus, United States)
Slit-Robo signaling is a key mediator of axon guidance decisions in divergent organisms ranging from planaria to
vertebrates. In Drosophila melanogaster, Commissureless (Comm) is a key post-translational regulator of the Robo
receptor and functions to prevent cell surface accumulation of Robo. Two additional Comm-family members are found in
Drosophila and they vary in their ability to regulate Robo receptors. Although all three Comm-family members can
complex with Robo receptors, only Comm and Comm2 regulate Robo receptor distribution in a Drosophila S2 cell culture
assay. In vivo loss-of-function and gain-of-function assays reveal prominent roles for Command minor roles for Comm2
during embryonic development. Structure-function studies suggest that the functional differences amongst Comm-family
members map to the trans-membrane and juxta-membrane regions of these proteins. Results from these ongoing studies
will be presented. We are also investigating the evolution of Comm-like genes and regulation of Slit-Robo signaling in
insects. The presence of Comm-family members in some insect orders (Diptera and Hemiptera) and apparent absence in
others (Lepidoptera and Hymenoptera) suggests a more ancient origin of Comm and the loss of Comm-like genes in some
but not all insect lineages. We are addressing the functional properties of divergent Comm-family members from a variety
of insects using several approaches, including the S2 cell culture assay. This work has been supported by a grant from the
National Science Foundation.
Program/Abstract # 367
Behavioral phenotypes after selective abrogation of Arx from the developing dorsal telencephalon
Simonet, Jacqueline C., University of Pennsylvania Cell and Developmental Biology, Philadelphia, United States; Marsh,
Eric; Golden, Jeffrey (Children's Hospital of Philadelphia, Philadelphia, PA, United States)
The aristaless-related homeobox gene (Arx) is mutated in many neurodevelopmental disorders all including neurocognitive
phenotypes. During development Arx is expressed in progenitor cells throughout the forebrain. In the pallium Arx is
expressed in the proliferative ventricular zone (VZ) where the excitatory neurons of the cortex are born. Arx-/y mice have
decreased proliferation in the VZ of the cortex resulting in a thinner cortex, however, these mice die soon after birth
precluding behavior analyses (Kitamura et al. 2002). Mice that have a point mutation or a poly-alanine track expansion in
Arx survive to adulthood and both were found to have learning deficits with the poly-alanine track expansion mice also
exhibiting anxiety and hyperactivity (Kitamura et al. 2009). To evaluate how Arx is affecting the development and
function of the excitatory neurons of the cortex, we conditionally eliminated Arx selectively from the precursors to all
cerebral cortical projection neurons without affecting the interneuron population. These mice lose upper layer neurons
resulting in a thinner cortex. The corpus callosum and the anterior commissure are hypoplastic or absent suggesting
cortical and possibly amygdala and hippocampal, connectivity are perturbed. Behaviorally these mice are less anxious,
more active, less social, and have focused learning deficits when compared to their wild type littermates. Furthermore,
compared to all other Arx mutant mice that have been studied, they do not have seizures. This mutant mouse provides an
important tool in which to study the function of Arx in brain development and behavior without seizures confounding the
analysis.
Program/Abstract # 368
A screen to identify interactors of the antiphosphatase Paladin in the neural crest
Stronge, Edward J.; Roffers-Agarwal, Julaine; Gammill, Laura S., University of Minnesota, Minnneapolis, United States