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Poster Full Abstracts - Cell Biology and Signal Transduction
Poster board number is above title. The first author is the presenter
184
189C
Eggshell patterning by Wishful thinking: signaling with positive feedback.
Rob Marmion
1
, Milica Jevtic
2
, George Pyrowolakis
2
, Nir Yakoby
1
. 1)
Department of Biology and Center for Computational and Integrative Biology, Rutgers University, Camden, NJ; 2) Institute for Biology I, Albert-Ludwigs-
University of Freiburg, Freiburg, Germany.
The
Drosophila
eggshell is an established model to study cell signaling, tissue patterning, and morphogenesis. The bone morphogenetic protein (BMP)
signaling pathway is a crucial regulator of tissue growth during multiple stages of
Drosophila
development. During oogenesis, the role of the type I BMP
receptor,
thickveins
(
tkv
), in regulating the spatial distribution of signaling and eggshell patterning, has been established. However, BMP signaling requires a
heterocomplex of type I and type II receptors. We found the type II receptor,
wishful thinking
(
wit
), to be non-uniformly expressed in the follicle cells (FCs),
which are a mono-layer of epithelial cells engulfing the developing oocyte. This pattern is spatially conserved in the FCs of multiple
Drosophila
species, and
it correlates with the domains of BMP signaling activity. We found WIT to be required for BMP signaling. In addition, targets of signaling were lost in cells
null for
wit
. Furthermore, we established wit as a transcriptional target of BMP signaling, and is thus maintained in a positive feedback regulatory loop. Of
importance, we demonstrate that WIT is essential for proper eggshell morphology. Previously, studies have limited WIT’s role to neurogenesis; however, we
demonstrate a role for WIT in non-neuronal tissue to control patterning and morphogenesis of the
Drosophila
eggshell.
190A
Connections between dorsal closure and head involution.
Matthew J. Moulton, Anthea Letsou. Department of Human Genetics, University of Utah, Salt
Lake City, UT.
The Drosophila embryo undergoes several important physiologic processes before transitioning to a larva. Among these processes are dorsal closure and
head involution. Both occur at approximately the same time during embryogenesis (8-12 hrs. AEL) and involve epithelial cell migration. Dorsal closure
occurs when leading edge cells signal to adjacent epithelial cells inducing them to change shape and cover the amnioserosa. Similarly, head involution
requires cellular signals to evoke changes in the epithelium to cover the head. Many mutants of the dorsal-open class not only fail to complete dorsal closure
but also fail to complete head involution. In many cases, it is known that head involution defects are secondary to defects in dorsal closure. Therefore, even
though both dorsal closure and head involution are morphologically similar, it is not clear whether they utilize the same or different molecular signals. Our
lab studies a series of embryonic lethal
mummy
(
mmy
) mutants that exhibit variably expressed dorsal closure and head involution defects.
mmy
encodes a
UDP-
N
-acetylglucosamine diphosphorylase which is responsible for producing sugars used to modify proteins, thus modulating their function. Some
mmy
mutants are able to complete dorsal closure but fail to head involute, revealing independent roles for
mmy
in controlling the molecular components involved
in these two processes. Here, we present our results from an analysis of embryonic cuticle phenotypes of several
mmy
alleles. We also present data using
engrailed
as a marker to track dorsal ridge formation and migration throughout development in
mmy
mutants. Our data indicate that
mmy
has independent
roles in dorsal closure and head involution. Identification of the Mmy-modified products in dorsal closure and head involution will enhance our molecular
understanding of these critical morphogenetic processes.
191B
Identification of genes that interact with
Drosophila auxilin
.
Susan M.L. Banks, William R. Stoutt, Janice A. Fischer. ICMB, MCDB, University of
Texas at Austin, Austin, TX.
Notch signaling is important for cell-cell signaling during development and is highly conserved across all multi-cellular organisms. Failure in Notch
signaling is causative in many human diseases. Studies in our laboratory are elucidating the signaling pathway and describing more general internalization
components functioning during signaling. In the eye, activation of the Notch pathway requires lqf(
Drosophila
Epsin)-dependent and clathrin-dependent
internalization of the Notch receptor ligands, Delta or Serrate, by the signaling cells. However, it is unclear exactly how and why ligand must be internalized
to activate Notch signaling. Recently, our laboratory found that in addition to clathrin and Epsin, Auxilin is essential for signaling and internalization of the
Notch ligand Delta. We showed that Auxilin is required for uncoating clathrin-coated vesicles to maintain a pool of free clathrin and Epsin in the cell. Using
auxilin
mutants as an entryway, I am attempting to identify previously unknown components of the Notch signaling pathway. An F1 EMS screen was
performed and seventeen complementation groups were identified as enhancers of the
auxilin
mutant phenotype. Among the seventeen genes identified are
Delta, lqf, hsc70, and faf
. Delta and epsin have known roles in the Notch pathway, specifically in terms of sending a signal. Hsc70 is an ATP-ase that binds
Auxilin to function in uncoating clathrin-coated vesicles. Faf maintains levels of active Epsin in the cell. These results suggest that I have isolated mutants in
genes closely tied to Notch signaling. Two mutants, previously undescribed in Notch signaling in the developing
Drosophila
eye, have been identified and
soon the identities of two more complementation groups will be known. When Notch signaling fails during eye development, it results in a rough eye
phenotype due to aberrant photoreceptor number and patterning. Preliminary results suggest the newly identified mutants are playing a role in Notch
signaling during eye development, as the photoreceptor mutant phenotype is enhanced in the screen mutants.
192C
Friend of Echinoid (Fred) and Echinoid (Ed) regulate EGFR trafficking.
Qian Nie, Susan Spencer. Department of Biology, Saint Louis University, St
Louis, MO.
The Epidermal Growth Factor Receptor (EGFR) is a receptor tyrosine kinase that regulates signaling pathways critical for cell proliferation and
differentiation in epithelial tissues. The amount of EGFR available for signaling is regulated by a balance of receptor recycling to the plasma membrane and
degradation in the lysosome. We have found that the immunoglobulin cell adhesion molecules Echinoid (Ed) and Friend of Echinoid (Fred) can regulate the
level of EGFR on the plasma membrane. Ed and Fred amino acid sequences are closely related, but Fred lacks the PDZ binding domain found at Ed’s C-
terminus. Here, using truncated and chimaeric forms of Ed and Fred, we examine the importance of Ed’s PDZ-binding domain in regulating internalization
from the plasma membrane. We also examine whether Fred’s effects on EGFR internalization require Ed. Our findings suggest that Ed’s PDZ-binding
domain promotes endocytosis of both Ed and EGFR from the cell surface. A possible model of how Fred and Ed regulate EGFR internalization will be
discussed.