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Poster Full Abstracts - Pattern Formation
Poster board number is above title. The first author is the presenter
317
693C
Reduced TOR Activity Promotes Cap-Independent Translation of Gurken During Drosophila Oogenesis.
Malachi A Blundon, Cara L. Doyle, Scott B.
Ferguson. Department of Biology, SUNY Fredonia, Fredonia, NY.
Gurken (Grk) expression is required to specify the polarity of the developing oocyte during Drosophila oogenesis. Proper localization and translation of
grk
transcripts is required to achieve proper axis specification.
gkr
translation initiation has been shown to be cap-dependent and require the activity of the
DEAD-box RNA helicase, Vasa. Vasa activity can be repressed by the ATK/Chk2-dependent meiotic checkpoint when DNA double strand breaks (DSBs)
persist in meiosis. Unrepaired DSBs in oocyte development of
spindle
-class mutants activate this checkpoint and result in inefficient
grk
translation and loss
of dorsal fates. This inefficient
grk
translation is thought to be related to reduced Vasa activity.
In a screen for suppressors of the ventralized eggshell phenotype seen in
spindle-B
BU
mutants, we identified mutations in the
lnk
and
PyK
genes. We show
that
lnk
and
PyK
mutations suppresses the eggshell phenotype independent of the DSB repair delay and Vasa phosphorylation seen in
spn-B
or
spn-A
mutants. This suggests that the eggshell phenotype is corrected by overcoming the translational block of
grk
transcripts seen in
spindle
mutants. Both Lnk
and PyK have been recently identified as members of the TOR signaling pathway. Direct inhibition of the TOR kinase with rapamyacin suppresses the
ventralized eggshell phenotype in
spn-B
or
vas
mutant females. Lnk and PyK modulate TOR kinase activity through different pathways that converge at the
TSC1/2 heterodimer. During dietary starvation, TOR activity inhibits cap-dependent translation by promoting the activity of the translation inhibitor eIF4E
binding protein (4EBP). We hypothesize that reduced TOR activity promotes
grk
translation independent of the ATR/Chk2 meiotic checkpoint pathway.
Recent data indicates that this may be achieved by way of IRES-dependent translation initiation of
grk
when TOR activity is low. This discovery suggests
flies are able to maintain the translation of developmentally important transcripts such as
grk
during periods of nutrient limitation.
694A
The role of the two promoter regions of
hunchback
in its RNA expression pattern in
Drosophila melanogaster
.
Maira A. Cardoso
1
, Márcio Fontenele
2
,
Helena Araujo
2
, Michelle Diniz
1
, Paulo M. Bisch
1
, Francisco J. P. Lopes
1
. 1) Institute of Biophysics Carlos Chagas Filho, University of Rio de Janeiro, Rio
de Janeiro, Rio de Janeiro, Brazil; 2) Institute of Biological Sciences, University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil.
Gene expression patterns during cell differentiation are determined by the regulatory activity of morphogenetic proteins on several genes. In
Drosophila
melanogaster
, the translation of the Bicoid (Bcd) mRNA, maternally anchored in the anterior pole of the embryo, produces a smooth protein gradient along
the embryo. The developmental gene
hunchback
(
hb
) interprets this Bicoid gradient in a position-dependent way, generating an expression pattern with a
sharp border in the middle embryo.
hb
regulation is controlled by two distinct promoter regions P1 and P2, and the spatial patterns of hb protein and
transcripts show remarkable differences, which have not been well characterized yet. Using specific RNA probes, we characterize the expression pattern of
transcripts regulated by both P1 and P2 promoter regions during nuclear cleavage cycle 14. Through fluorescent in situ hybridization and protein staining we
simultaneously determined the dynamics of the Hb protein and the transcripts derived from P1 and P2. By expanding a previously proposed model (Lopes, et
al., PloS Comput. Biol., 2008), we developed a predictive regulatory network model describing the expression pattern of Hb protein and the
hb
transcripts
from both regulatory regions. Our experimental and theoretical approaches allow understanding the role of P1 and P2 regions for generating a central strip in
the
hb
expression pattern, called parasegment 4. We show that bistability plays a central role to produce this key structure during the
Drosophila
embryonic
development.
695B
Functional Convergence in Embryonic Patterning Determinants.
Rhea R. Datta, Jackie Moore, Gozde Yucel, Stephen Small. Department of Biology,
New York University, New York, NY.
Homeodomain (HD)-containing proteins control embryonic patterning events in all metazoans. Structural changes in these proteins can result in
developmental defects and disease, and can drive speciation events when fixed in a population. The HD containing transcription factor Bicoid (Bcd) is
responsible for the patterning events that drive anterior determination in Drosophila melanogaster, and can activate over 40 zygotic targets in the embryo as
well as repress translation of posterior proteins. Bcd, while essential for Drosophila development, is not conserved outside higher Diptera. Rather, known
anterior embryonic patterning events in other insects are controlled by the HD protein Orthodenticle (Otd). In a fascinating regulatory network twist, otd has
evolved to become a strict zygotic target of Bcd in Drosophila. Moreover, the Bcd paralog Zerknullt (Zen) has no role in anterior patterning, suggesting that
these genes are under strong selection. We examine the role of HD and amino-acid specificity in activating target genes required for anterior patterning
functions. Through key chimeric rescue assays (both with HD swaps and single residue changes), we show that there is some functional convergence
between Bcd, Zen and Otd. Maternally supplied Otd is capable of rescuing many anterior structures in bcd mutants, while Zen cannot. We show that Otd can
activate Hb, but not Gt expression, and that we can systematically restore Bcd function by adding key resides into Otd-HD. While boundaries of gene
expression remain unaffected, we find that swapping BcdHD into Otd and Zen backbones cannot rescue bcd mutants completely. By using this chimeric
protein rescue, we hope to link protein structural motifs with specific embryonic patterning functions. In addition to identifying the protein structural
requirements for anterior patterning, this work examines the molecular basis for understanding how anterior determinants evolve, both functionally and
structurally.
696C
Negative regulation of Epidermal Growth Factor Receptor signalling in the ovary.
Scott De Vito
1
, Jean-François Biosclair Lachance
1,2
, Mariana
Fregoso Lomas
1
, Laura Nilson
1
. 1) Department of Biology, McGill University, Montreal, Quebec, Canada; 2) Department of Biological Sciences, University
of Chicago, Chicago, IL, USA.
During oogenesis the follicular epithelium, which overlies the growing oocyte, is patterned to form the structures present in the eggshell, including two
dorsal anterior appendages separated by a dorsal midline domain. The primordia that form these structures are marked by differential expression of the
Broad transcription factor complex. Expression of this fate marker is controlled by dorsally localized activation of Epidermal Growth Factor Receptor
(EGFR) in the follicle cells by its secreted ligand Gurken (Grk) from the oocyte. We are studying how alterations of EGFR activity lead to changes in the
patterning of this tissue. For example, when the negative regulator Sprouty (Sty) is lost, dorsal fates are expanded ventrally as predicted from the expected
increase in EGFR activity. Unexpectedly, these domains are also shortened along the anterior posterior (AP) axis. Here we look at two other negative