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Poster Full Abstracts - Cell Biology and Signal Transduction
Poster board number is above title. The first author is the presenter
191
luciferase assay.
217A
Refinement of the JAK/STAT Genetic Circuit in Border Cell Recruitment and Detachment.
Amanda J. Monahan, Michelle Starz-Gaiano. Department
of Biological Sciences, University of Maryland, Baltimore County, Baltimore, MD, 21250.
The genetic regulation that triggers a cell to transition from non-migratory to migratory is incompletely understood despite its role in many processes
during normal development and pathological events. The process of border cell specification is an exemplary model to investigate how epithelial cells are
converted into a migratory state. In the egg chamber, high levels of the activated transcriptional regulator Signal Transducer and Activator of Transcription
(STAT) converts a subset of epithelial follicle cells into a collective migratory cluster, called the border cells, while adjacent cells are left behind. Cells
excluded from the border cell cluster initially activate STAT signaling but then exhibit a significant decrease in active STAT relative to their neighbors, and
this downregulation is required for proper border cell migration. A proposed STAT-activated genetic circuit employs pro-migratory and inhibitory cues to
limit the number of motile cells.
apontic
and its downstream target,
miR-279
, are known components that feedback negatively on STAT signaling. We have
identified an additional component to this negative feedback circuit in follicle cells-
suppressors of cytokine signaling (socs)36e
. Members of the highly
conserved SOCS family have been shown to be downstream targets and attenuators of STAT signaling. In the egg chamber, a hypomorphic allele of
socs36e
results in extra follicle cells becoming invasive - a phenotype similar to loss of function
miR-279
or hyperactive STAT. Furthermore, we have observed a
genetic interaction between
apontic
and
socs36e
, indicating
socs36e
may be a downstream target of both STAT and APT. Thus, our results demonstrate that
the combined functions of
miR-279
and
socs36e
may be sufficient to account for APT’s negative regulation on STAT activity.
218B
The Distribution of the JAK/STAT Ligand Unpaired (Upd) During Oogenesis.
Dustin W. Perry, Travis R. Sexton, Douglas A. Harrison. Department of
Biology, University of Kentucky, Lexington, KY.
Morphogens are molecules that can directly specify different cell fates in a concentration dependent manner. During Drosophila development, much focus
has been given to the Wnt (Wg), Hedgehog (Hh) and TGF-β (Dpp) ligands for their abilities to behave as morphogens. Using a novel system in which to
study morphogens, the Drosophila ovary, we report on another morphogen, Unpaired (Upd). Upd is a member of the Unpaired ligand family that activates
the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling in Drosophila. Previous work with Upd showed that it is
glycosylated, secreted, and bound to the extracellular matrix. Upd can be released from the ECM with heparin, suggesting Upd may bind to Heparan Sulfate
Proteoglycans (HSPGs). In the ovary, the JAK/STAT pathway is activated in a graded fashion and the level of JAK signaling is sufficient to determine
anterior follicular cell fates. Antibody staining against Upd shows that once released from its source in the ovary, there is a clear graded distribution along
the apical surface of the epithelium. Mosaic clonal analysis has revealed that loss of one of the four known HSPGs, Dally, causes a reduction in JAK
signaling and extracellular Upd accumulation in egg chambers in the vitellarium. A stretch of positively charged amino acids near the N-terminus of Upd
affects interactions with the ECM. Our data support a role for Dally in stabilization of the extracellular Upd, by retaining it to the ECM, preventing its
degradation. The Drosophila ovum presents a novel model for morphogen signaling with distinct advantages for ligand tracking and manipulation of
extracellular environment.
219C
Elucidating the mechanism by which Apontic inhibits JAK/STAT activity.
Afsoon Saadin, Michelle Starz-Gaiano. University of Maryland Baltimore
County, Baltimore, MD.
Cell migration, which is required for various desired biological events, is also the cause of an undesired phenomenon, tumor metastasis. Out of different
signaling pathways that contribute to cell migration, the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) is of high interest since
this pathway is involved in various biological processes, and dysfunction of the pathway is correlated to different human diseases, including immune
disorders and tumorigenesis. Some components of this pathway including DOME, UNPAIRED, JAK and STAT are well characterized, however, other
components of the pathway including APT and SOCS are not completely understood. It has been shown that APT and SOCS36E are negative regulators of
the pathway and they both affect cell migration, however, the mechanism by which they act is not clear. It is known that APT inhibits STAT activity
indirectly. To identify the component/s of the pathway that mediate the regulatory function of APT, we have taken advantage of a STAT Luciferase reporter
assay and RNAi technology in S2 cells. We confirmed that knockdown of
socs36e
led to higher STAT reporter expression. We also found that cells change
transcription activity levels non-linearly in response to higher or lower levels of APT expression. We also show that cells that over-express APT and have
reduced SOCS36E, have increased STAT activity, suggesting that SOCS36E is one of the components through which APT functions. Further experiments
are aimed towards understanding the mechanistic relationship between APT and SOCS36E.
220A
The effect of Upd3 on stem cells in Drosophila testes.
Lingfeng Tang, Douglas Harrision. Department of Biology, University of Kentucky, Lexington,
KY.
The Drosophila testis serves as a perfect model for investigating stem cells. Besides the sheath, the testis is only composed of 3 lineages of cells: hub cells,
germline cells and somatic cyst cells. At the tip of testes is the hub, which is composed of 9-12 cells. The germline stem cells (GSCs) and somatic stem cells
(SSCs) directly attach to the hub. JAK/STAT activity which is activated by Upd, the ligand of the pathway, serves as the molecular niche of both GSCs and
SSCs in the testes. Upd activates JAK/STAT pathway in SSCs directly, then SSCs affect GSCs through TGF-beta signaling. It has been reported that loss of
function of Stat92e leads to the loss of both GSCs and SSCs in testes, and ectopic activation of Stat92e leads to ectopic stem cell like germline cells. Mutants
for Upd3, another JAK pathway ligand, have recently been found to exhibit reduced lifespan and premature male reproductive senescence. Reduced lifespan
could be an indication of accelerated aging of flies. As an alternative, Upd3 mutations may lead to reduced JAK/STAT activity in testes, which may
subsequently impair the maintenance of GSCs and SSCs in testes. These alternatives can be distinguished by the phenotypes of upd3 mutant males as they
age. If aging is accelerated in testes we would expect thinner testes, less GSCs and SSCs and decreased cell division rate which are normally observed as the
fly ages. If Upd3 mutation leads to reduced JAK/STAT activity we would expect more GSCs, less SSCs and lower expression of beta PS integrin which are