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Poster Full Abstracts - Regulation of Gene Expression
Poster board number is above title. The first author is the presenter
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miRNAs, but the effect of serum deprivation on the miRNA machinery at the mechanistic level is still poorly understood. We set out to extend the
understanding of miRNA response to serum deprivation and its mechanism at the molecular level. By taking advantage of density gradient centrifugation,
we found that upon serum deprivation in S2 cells, denser Ago1-associated-complexes rapidly form in addition to the pre-existing Ago1-complexes under the
serum-fed condition. Interestingly, the dense Ago1-complexes can be further identified as two pools, one pool being observed as the denser pool than the
other. Treating serum-deprived cells with various reagents and drugs targeting candidates of required factors reveals distinct dependence of these Ago1-
complexes on the presence of long RNA, membranes, polysomes, and active protein synthesis. Furthermore, the well-characterized and important Ago1-
binding partner, GW182, is only detected in the least dense pool of Ago1-complex but not the denser pools. These results suggest that miRISC is a dynamic
complex capable of adapting to the environmental stimuli by modifying its assembly and possibly its function, thereby reprograms the global gene
expression that a cell calls for when facing extracellular challenges.
799A
Drosophila miR-9a guards organism’s homeostasis by regulating stress response protein Dystroglycan.
Andriy S Yatsenko, Halyna R Shcherbata.
Gene Expression and Signaling, Planck Institute for Biophysical Chemistry, Goettingen, Germany.
MicroRNAs (miRNAs) are small non-coding RNAs that function as negative regulators of gene expression. miRNAs bind to the 3`UTR region of their
target mRNAs and lead to translational inhibition. Despite the fact that many miRNAs have been identified in Drosophila their function in regulating
development and tissue maintenance is not completely understood. Here we show that miR-9a is required for response to stress. Changing the ambient
temperatures and applying energetic stress to miR-9a mutants increases embryonic lethality and shorten lifespan in adults when compared to wild type
animals. Interestingly, on elevated temperatures the expression level of miR-9a is decreased and vice versa. In addition we found that miR-9a mutants have
higher metabolic rate measured by CO2 production. Dystroglycan (Dg) is a predicted target for miR-9a and has been previously shown to be required for
stress response, muscle tissue homeostasis and control of metabolic rate in Drosophila. In the embryo miR-9a and Dg have reciprocal expression patterns
and changing the levels of miR-9a affects amount of Dg protein. Since Dg misregulation disrupts tissue homeostasis and increases sensitivity to stress we
propose that miR-9a is important for maintaining homeostatic Dg expression levels during development and stress response.
800B
Autoregulation and context-specific regulation of the Yan/Pnt bistable network.
Lauren Cote, Jie Zhang, Jemma L. Webber. Univ Chicago, Ben May
Dept Cancer Research, Chicago, IL.
Downstream of receptor tyrosine kinase (RTK) signaling, two ETS-family transcription factors Yan and Pnt, a repressor and an activator respectively, are
thought to form a bistable switch controlling cell-fate decisions (Graham et al, 2010). RTK signaling induces Yan degradation and thus derepression of
target genes, and concomitant Pnt activation and thus activation of target genes. Genome-wide binding profile analysis of the repressor Yan identified large
enrichment domains containing multiple peaks over tens of kilobases termed high density regions. Conservation of this chromatin association pattern in
D.
virilis
and its presence at multiple developmentally important genes indicate that it might be functionally relevant for proper and robust gene expression. One
of the most prominent examples of this high density signature is found at the
yan
locus, leading us to hypothesize that Yan autoregulation via transcriptional
repression is important for the function and stabilization of this cell-fate decision network. To test this hypothesis, we are investigating the ability of Yan to
repress itself using recombineered constructs which delete various Yan binding regions from the
yan
locus. In addition, we are exploring the ability of the
activator Pnt to regulate Yan expression in different developmental contexts. These preliminary results point to autoregulation and developmental context as
contributors to the network topology which ensures precise expression of target genes and buffers against intrinsic and extrinsic perturbations.
801C
Bicaudal-C represses
nanos
mRNA in
Drosophila
oogenesis through a direct association with a 3’ UTR motif distal to the translational control
element.
Chiara Gamberi. Biology, McGill University, Montreal, Canada.
nanos
(nos) mRNA encodes a key determinant of posterior embryonic patterning in
Drosophila
. Expression of Nos is temporally and spatially regulated by
several proteins that interact with its mRNA and control its translation and/or its localization to the posterior of the oocyte. We provide evidence that
Bicaudal-C (Bic-C) interacts directly with an element in the
nos
3’ UTR, negatively regulating its expression in early to mid-oogenesis through an effect on
its polyadenylation state. In
Bic-C
mutants, or when forms of
nos
mRNA that are mutated for the Bic-C interaction site are expressed, ectopic Nos is
produced that accumulates in large structures in the cytoplasm of the nurse cells. We further show that, unlike in the pole plasm,
oskar
activity is not
required for Nos expression earlier in oogenesis. These results further elaborate the complexity of post-transcriptional regulation of
nos
.
802A
The DEAD-box RNA helicase,
belle
, provides post-transcriptional control to steroid-triggered responses during
Drosophila
metamorphosis.
Robert
Ihry
1,2
, Arash Bashirullah
1
. 1) Division of Pharmaceutical Sciences, University of Wisconsin-Madison, Madison, WI; 2) Graduate Program in Cellular and
Molecular Biology, University of Wisconsin-Madison, Madison, WI.
The steroid-hormone ecdysone, through its receptor heterodimer (EcR/USP), directly induces the expression of a small set of target genes; these “early”
response genes in turn induce expression of a larger set of secondary or “late” response genes. Here, we show that post-transcriptional control is critical for
late gene induction and the self-limiting nature of the ecdysone-triggered transcriptional cascade. We identified
belle
in a forward genetic screen for
mutations that disrupt one ecdysone-triggered process (the destruction of larval salivary glands during metamorphosis) but not other responses to the same
pulse of ecdysone. In
belle
mutant larval salivary glands, the ecdysone-triggered induction of
reaper
and
hid
is disrupted even though other ecdysone
induced genes are not affected. We show that this defect is due to the failure to translate the early gene
E74A
. We show that, although the
E74A
mRNA is
induced in a broad peak, E74A protein is expressed in a very short pulse and that the timing of E74A protein determines the timing of the death response.
Moreover, we show that this transient pulse of E74A protein is generated by a feed-forward loop between
E74A
and
belle
. In addition, we show that E74A
protein is critical for limiting its own transcription and that of other early response genes, demonstrating its critical role in the self-limiting behavior of the
ecdysone-triggered transcriptional cascade. Together our results suggest that post-transcriptional control is critical for the proper function of steroid-triggered
transcriptional responses.