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Poster Full Abstracts - Cell Biology and Signal Transduction
Poster board number is above title. The first author is the presenter
186
197B
Gliotactin functionally interacts with Discs-Large through phosphotyrosine signaling and a PDZ binding motif.
Mojgan Padash-Barmchi, Kendra
Sturgeon, Vanessa J. Auld. Dept. of Zoology, Health Science Institute, University of British Columbia, Vancouver, Canada V6T1Z3.
Establishment and maintenance of permeability barriers (PB) is one of the most important functions of the polarized epithelial cells. PB in Drosophila
epithelia is established by septate junctions (SJs) between two adjacent cells and by tricellular junctions (TCJs) at the contact site of three epithelial cells.
The transmembrane protein Gliotactin (Gli) is uniquely localized to the TCJ and is necessary for PB maintenance. Tight control of the level and localization
of Gli by tyrosine (Y) phosphorylation is important for localization of Gli to the TCJ and survival of epithelial cells. We are interested in understanding of
the importance of this tight regulation in the epithelial cells. We used site directed mutagenesis as well as the UAS-Gal4 expression system to investigate the
importance of precise localization of Gli to the TCJ. We have previously shown that blocking endocytosis causes mislocalization of Gli to the SJ and results
in cell delamination and death. Here, we show that this mislocalization results in downregulation of the tumor suppressor protein, Discs Large (Dlg).
Blocking the downregulation of Dlg causes severe tissue overgrowth and apoptotic cell death. We show that Gli functionally interacts with Dlg and this
interaction requires Y phosphorylation and the PDZ binding motif of Gli. The tissue overgrowth as well as apoptosis caused by coexpression of Gli and Dlg
requires phosphorylation of Dlg at serine 797. Blocking this phosphorylation completely prevents those phenotypes. We further find that Drosophila JNK
acts downstream of Gli and Dlg to mediate the overgrowth phenotype caused by coexpression of Gli and Dlg. Our results suggest that correct localization of
Gli to the TCJ is important and there is a cellular mechanism that compensates for the presence of ectopic Gli at the SJ by reducing the level of Dlg to
diminish the severe defects resulted from interaction of Gli with Dlg at the SJ.
198C
Spatial and temporal regulation of cell adhesion in Drosophila is mediated by the bHLH transcription factor Delilah.
Adi Salzberg, Atalya Nachman,
Nirit Egoz, Naomi Halachmi, Moran Toder. Rappaport Fac Medicine, Technion-Israel Ins Technology, Haifa, Israel.
How transcription factors and signaling networks specify cell fates is a central question in developmental biology. Although we have a conceptual picture
of how differential gene expression is used to generate different types of cells, we still lack a full understanding on how any cell is specified and how it
acquires its unique properties. In a recent work we have identified the bHLH transcription factor Delilah (Dei) as an important regulator of cell adhesion in
Drosophila. We have demonstrated that in organs in which sub-groups of cells differentiate into more adhesive (‘sticky’) or less adhesive cell types, Dei is
expressed in the stickier cell types. In these cells Dei is required for inducing proper level of expression of βPS integrin. Based on these observations we
think of Dei as a molecular switch that turns on βPS integrin expression wherever a sticky cell has to develop. Since such a switch needs to be turned on in
different tissues and different developmental and physiological contexts, it is predicted that the
dei
gene would be able to respond to various signaling
pathways and transcription factors. Indeed, when we analyzed the regulatory region of
dei
, using
lacZ
reporter constructs, we found that the regulatory
region of the
dei
locus harbors multiple discrete regulatory modules that drive expression in different subsets of the
dei
-expressing cells and respond to
different transcription factors. This observation supports the idea that spatial and temporal regulation of cell adhesion in Drosophila is mediated, at least in
part, by the regulated expression of Dei.
199A
Regulation of integrin turnover by force in vivo.
Guy Tanentzapf
1
, Mary Pines
1
, Stefan Czerniecki
1
, stephanie Ellis
1
, Raibatak Das
2
, Daniel Coombs
2
. 1)
CPS Dept, Univ British Columbia, Vancouver, BC; 2) Mathematics Dept. Univ British Columbia, Vancouver, BC.
We are interested in understanding how complex tissue architecture forms during development and once formed how it is maintained throughout the life of
the organism. In particular our lab studies the role of cell adhesion and the cytoskeleton in the context of development with an emphasis on integrins, the
major receptors for the ECM in the fly. A fundamental question in developmental biology is how tissue structure is stabilized at the completion of
embryogenesis. During embryonic development tissues undergo substantial remodeling and adhesion must be dynamic but post-embryonically stable
adhesion maintains tissue architecture over the long term and must be stable. Our work is designed to address the question of how the transition from
dynamic to stable adhesion is mediated. To this end we have developed methodologies that allow us to study the dynamics of the adhesion complex in vivo
in live embryos and larva using Fluorescence Recovery After Photobleaching (FRAP). In addition we are utilizing mutations that make it possible to
conditionally decrease or increase the force imposed on integrin-mediated adhesions. Using these approaches we have uncovered an essential role for
mechanical force in regulating integrin turnover and importantly in stabilizing cell adhesion at the completion of embryogenesis. Finally, using a set of point
mutations in integrins and their associated proteins we have been able to specifically address the mechanisms that underlie the stabilization of adhesion at the
completion of embryogenesis.
200B
Expression and functions of Drosophila Mmp1 and Mmp2 in Drosophila oogenesis.
Xiaoxi Wang, Kimberly LaFever, Andrea Page-McCaw.
Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN.
Matrix metalloproteinases (MMPs) are matrix-degrading proteinases. They play crucial roles in many physiological processes by remodeling extracellular
matrix (ECM) and by regulating signaling pathways. Drosophila melanogaster provides an excellent model for studying the physiological functions of
MMPs because of its superb genetics and because there are only two evolutionary conserved, non-redundant MMPs in the genome. Here we address the
functions of Drosophila Mmp1 and Mmp2 in Drosophila oogenesis. Mmp2 temperature sensitive mutants are female-sterile and display egg chamber
degeneration, indicating an indispensable role of Mmp2 in oogenesis. By using a partially-rescuing genomic construct expressing C-terminal EGFP fusion,
we localized Mmp2 to the terminal filament cells and cap cells, which are the niche cells for both germline stem cells and somatic stem cells. Interestingly,
Mmp1 is also expressed in those cells, as well as on the basement membrane underlying follicle cells in the germarium and early stage egg chambers. Mmp1
expression diminishes starting from stage 6 egg chambers and is restricted to stalk cells thereafter, which is concurrent with the switch of follicle cells from
mitosis to endoreplication. We hypothesized that Drosophila Mmp1 and Mmp2 play important roles in oogenesis by regulating stem cells niche signaling
or/and by regulating the remodeling of extracellular matrix of proliferating pre-follicle cells.
201C