Congress Abstracts - Society for Developmental Biology

Program/Abstract # 564
Withdrawn
Program/Abstract # 565
ADAM10 and ADAM19 proteolytically process Cadherin6B during epithelial-to-mesenchymal transitions of the cranial neural
crest
Schiffmacher, Andrew T.; Taneyhill, Lisa (U Maryland, USA)
Epithelial-to-mesenchymal transitions (EMTs) occurring in chick cranial neural crest cells permit these cells to delaminate from the
neuroepithelium en masse, acquire motility, and emigrate from the dorsal neural tube. Epithelial adherens junction disassembly is an
essential component of this EMT process. Within the premigratory neural crest domain, N-cadherin and Cadherin6B (Cad6B) are
downregulated prior to completion of EMT, and this loss of protein is necessary for proper cranial neural crest emigration. While
Cad6B downregulation is controlled in part by Snail2-mediated transcriptional repression, we hypothesize that post-translational
mechanisms are also utilized to promote the observed rapid turnover of Cad6B protein due to its usual long half-life. For the first time
in vivo, we demonstrate the presence of a putative N-terminal fragment (NTF) generated by Cad6B proteolysis that correlates with a
reduction in full-length Cad6B and the onset of EMT. Importantly, we note the concomitant appearance of two C-terminal cleavage
fragments (CTFs) that are absent in embryos treated with a broad-spectrum metalloproteinase inhibitor (GM6001). By co-expressing
relevant proteases with Cad6B in vitro, we identified that A Disintegrin and Metalloproteinases (ADAM) ADAM10 and ADAM19,
along with γ-secretase, cleave Cad6B to give rise to the NTF and CTFs previously observed in vivo. As both ADAMs are expressed in
the appropriate spatio-temporal pattern to process Cad6B in vivo, they were assessed for Cad6B proteolytic activity in vivo.
Overexpression of either ADAM within premigratory cranial neural crest cells prior to EMT results in premature loss of Cad6B
protein. Together, these results suggest a two-part mechanism for Cad6B proteolysis involving ADAM10, ADAM19, and γ-secretase
during cranial neural crest cell EMT.
Program/Abstract # 566
Ephrin signaling maintains apical adhesion of neural progenitors
Davy, Alice; Arvanitis, Dina (CBD, France); Behar, Annie (IPBS, France); Tryoen-Toth, Petra (INCI, France); Bush, Jeff (UCSF,
USA); Jungas, Thomas (CBD, France); Vitale, Nicolas (INCI, France)
Apical neural progenitors are polarized cells whose apical membrane is the site of cell-cell and cell-extracellular matrix adhesion
events that are essential to maintain the integrity of the developing neuroepithelium. Apical adhesion is important for several aspects
of the nervous system development including morphogenesis and neurogenesis, yet the mechanisms underlying its regulation remain
poorly understood. Herein, we show that ephrin-B1, a cell surface protein that engages in cell signaling upon binding cognate Eph
receptors, controls normal morphogenesis of the developing cortex. Efnb1 deficient embryos exhibit morphological alterations of the
neuroepithelium which correlate with neural tube closure defects. Using loss-of-function experiments by ex vivo electroporation we
demonstrate that ephrin-B1 is required in APs to maintain their apical adhesion. Mechanistically, we show that ephrin-B1 controls
cell/ECM adhesion by promoting apical localization of integrin-beta1 and we identify ADP-ribosylation factor 6 (ARF6) as an
important effector of ephrin-B1 reverse signaling in apical adhesion of APs. Our results provide evidence for an important role for
ephrin-B1 in maintaining the structural integrity of the developing cortex and highlight the importance of tightly controlling apical
cell/ECM adhesion for neuroepithelial development.
Program/Abstract # 567
The regulation of epithelial cell adhesive forces by the MID1/Alpha4/PP2Ac complex and its implications for cleft lip
susceptibility
Cox, Timothy C. (U Washington, USA), Huang, Yongzhao; Koto, Cathy (Seattle Children's Res Inst, USA)
The embryonic orofacial epithelium facilitates the fusion of converging facial prominences that is essential for proper oronasal form
and function. Failure to properly fuse these prominences results in cleft lip/palate (CLP), one of the most common birth defects, yet
little is known about the role of causative genes. MID1 is a microtubule-associated E3 ubiquitin ligase, the loss of which results in a
syndromic form of CLP. MID1 interacts strongly with Alpha4, the mammalian homolog of yeast Tap42. As in yeast, Alpha4 binds the
catalytic subunit of protein phosphatase 2A (PP2Ac) to uniquely regulate its activity and that of the TOR pathway. We report here that
perturbation of MID1 function in polarized MDCK cells results in reduced cell-cell adhesive strength and altered cell-ECM
interactions, with concomitant changes in mTOR phosphorylation, Rac1 activation, and phospho-FAK levels. In non-polarized cells,
disruption of MID1 reduces adhesion to laminin but not collagen, and perturbs collective migration. Taken together, our data suggest
that mTOR/Rac1 signaling is the downstream pathway affected by the MID1/Alpha4 axis in the regulation of epithelial cell adhesion.
In support of the importance of this epithelial function of MID1 during formation of the upper lip, in ovo electroporation of the same
dominant-negative form of MID1 into chick pre-fusion orofacial epithelia was found to result in cleft lip in this species. Ongoing
studies using fabricated micropost technology are aimed at determining the relative contributions of different downstream effectors of
MID1 and quantifying their impact on intercellular adhesive forces. These studies provide the first clues as to the cellular mechanisms
responsible for CLP.
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