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Poster Full Abstracts - Cell Death
Poster board number is above title. The first author is the presenter
221
dramatically in length and diameter as the larva increases in size 1000-fold over the four day larval period. We identified mutations in
uninflatable
(
uif
) that
show specific reductions in tracheal length, such that at the end of the third instar the
uif
mutant trachea are roughly half the relative length of trachea in wild
type animals.
uif
encodes a large transmembrane protein with carbohydrate-binding and cell signaling motifs in the extracellular domain. It is expressed in
ectodermally derived epithelial cells, but is most strongly expressed in the trachea, where it localizes to the apical plasma membrane. To our knowledge,
only one other gene has a similar mutant phenotype:
Matrix metalloproteinase 1
(
Mmp1
).
Mmp1
encodes a secreted protease involved in remodeling the
extracellular matrix. Mmp1 is strongly expressed in tracheal cells where it localizes to cellular junctions and to the apical surface. To explore the relationship
between
uif
and
Mmp1
, we examined the expression and localization of each protein in loss-of-function mutations in each gene. Whereas Uif expression and
localization are unaffected in
Mmp1
mutant trachea, Mmp1 localization is altered in
uif
mutant animals. Specifically, a large portion of Mmp1 protein is
found in punctate structures in the cytoplasm. We are currently attempting to understand how
uif
regulates Mmp1 localization, and are conducting genetic
rescue experiments in order to place
uif
and
Mmp1
within the InR/PI3K - TOR pathway.
331A
The role of the AP-4 transcription factor
cropped
in imaginal disc growth and regeneration.
Sutton Matt, Halme Adrian. Department of Cell Biology,
University of Virginia School of Medicine, Charlottesville, VA.
Drosophila
imaginal discs have a remarkable capacity to regenerate following damage. To better understand the genetic pathways that mediate this
regenerative process, we have begun to examine the role of the AP-4 transcription factor Cropped in imaginal tissue homeostasis. We have shown that
cropped
expression is increased in damaged tissues. Using clonal analysis to examine the growth of
cropped
mutant tissues during normal development and
during regenerative growth, we have found that weaker hypomorphic alleles of
cropped
exhibit regeneration-specific growth defects, whereas stronger
amorphic alleles of
cropped
display defects in both regenerative growth and growth in undamaged tissues. We have found that the inhibition of amorphic
cropped
clone growth during normal disc development can be attributed to a substantial amount of cell death within these clones. We have found that
cropped
clones can be rescued by introducing a heterozygous
Minute
mutation into the genetic background, suggesting that amorphic
cropped
clones are
eliminated by cell-competition. We are currently examining whether
cropped
activity regulates competitive cell interactions and whether cell-competition
plays an important role during imaginal disc regeneration.
332B
Non-autonomous tumor progression driven by mitochondrial dysfunction.
Shizue Ohsawa
1
, Yoshitaka Sato
1
, Masato Enomoto
1
, Mai Nakamura
1
, Aya
Betsumiya
1
, Tatsushi Igaki
1,2
. 1) Department of Cell Biology, G-COE, Kobe University Graduate School of Medicine, Kobe; 2) PRESTO, Japan Science and
Technology Agency, Japan.
Tumor progression is accomplished by both intra- and inter-cellular cooperation of oncogenic alterations. However, the underlying mechanism of how
each oncogenic mutation cooperates with other mutations to progress toward malignancy through cell-cell communications remains elusive. We performed a
genetic screen in
Drosophila
for identifying genes that drive non-autonomous tumor progression. Clones of cells expressing oncogenic Ras (RasV12) result
in the formation of benign tumors in eye imaginal epithelium. We introduced additional mutations in RasV12-tumors and screened for mutants that cause
non-autonomous overgrowth of surrounding wild-type tissue. We identified a series of mutations that affect the function of mitochondrial respiratory chain
as responsible genes of these mutants. Intriguingly, when RasV12-expressing clones were induced nearby these mutant clones, the RasV12-tumors not only
overgrew but acquired metastatic ability. The molecular mechanism by which Ras activation and mitochondrial dysfunction cooperate to drive non-
autonomous tumor progression will be discussed.
333C
Identification of the gene disrupted in
fried
mutants.
Kimberley Seoane, Henrique Valim, Jason Morris. Dep't of Natural Sciences, Fordham University,
New York, NY.
Drosophila
fried
mutants were originally isolated in a clonal screen for oogenesis defects.
fried
mutant egg chambers exhibit reduced endoreplication in
nurse cells and abnormal morphology of chromosomes in nurse cells and oocytes.
fried
homozygotes arrest as larvae. Deficiency mapping and
complementation testing and sequencing of candidate genes enabled us to identify the gene affected in
fried
mutants. One allele,
fried
150
, is disrupted by a 61
bp deletion early in the gene and is a likely candidate for a null allele. The second allele,
fried
212
, displays a weaker phenotype and encodes a nonsense
mutation later in the protein. Mutations in this gene have not been isolated previously in Drosophila, and the closest homologs of the gene have not been
analyzed in other systems. We are currently attempting to generate antibodies against Fried protein and we are carrying out experiments with rescue
constructs in order to study the function of Fried in development.
334A
Regulation of the archipelago ubiquitin ligase subunit by a dynein light chain.
Daniel Allyn Barron, Kenneth Moberg. Dept Cell Biol, Emory Univ Sch
Med, Atlanta, GA.
Carcinogenesis is fueled by the inactivation of tumor suppressor genes, which allows for excessive cell growth and division. FBXW7 (F-box/WD protein
7) and archipelago (ago) are orthologous tumor suppressor genes in humans and Drosophila melanogaster, respectively, that encode a conserved component
of an E3 ubiquitin ligase that targets pro-proliferative substrates for proteasomal degradation. FBXW7 is biallelically inactivated in a wide range of human
cancers including primary endometrial, colorectal, and prostate tumors. Although several pro-proliferative targets of FBXW7/Ago-mediated degradation
have been identified (e.g. Cyclin E and Myc), the upstream regulation of FBXW7/Ago has not been studied extensively. We have used Drosophila as a
model to address the role of Cut Up (Ctp; aka LC8 or dlc-1), a cytoplasmic dynein light chain protein, as a potential antagonist of the Ago Ub ligase. Yeast
two-hybrid data suggests that Ctp physically interacts with Ago, and loss of Ctp (due to either a hypomorphic allele or inverted repeat knockdown) leads to a
reduced growth phenotype that can be dominantly modified by ago null alleles. Furthermore, dMyc, a pro-proliferative target of the Ago Ub ligase, has
reduced steady-state levels in cells lacking Ctp, suggesting that Ctp acts to inhibit Ago activity. In sum these genetic and molecular data suggest there is a
physiologically relevant interaction between ago and ctp in imaginal disc cells. As Ctp antagonizes the pro-apoptotic activity of the protein Bim by
sequestrating Bim to dynein motor complexes (Puthalakath et al, 1999), we hypothesize that Ctp inhibits Ago-mediated turnover of pro-proliferative