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Poster Full Abstracts - Pattern Formation
Poster board number is above title. The first author is the presenter
320
cascades. Found within this tissue is the Retinal Determination Gene Network (RDGN); a dynamic signalling network which includes
twin of eyeless (toy),
eyeless (ey), sine-oculus (so), eyes absent (eya), dachshund (dac)
, among other factors. Additionally, signalling factors such as Dpp, Hh, N, and Wg, feed
into multiple points in the RD network having both protagonistic and antagonistic effects in a context dependent manner. Homedomain interacting protein
kinase (Hipk) is a conserved serine threonine kinase and has been reported to act in multiple signalling pathways. Previous studies have shown that
hipk
plays a role in Notch mediated growth of the
Drosophila
eye imaginal disc by antagonizing the global co-repressor Groucho. Here we provide evidence that
hipk
holds additional roles in eye development and eye specification. Loss of
hipk
leads to partial and or complete loss of both the compound eye and the
ocellar complex similar to phenotypes observed with loss of RDGN components. Conversely, overexpression of
hipk
induces ectopic eye fields on the head,
abdomen and in rare cases the leg disc. Preliminary ectopic eye assays with overexpression of
toy
reveal that modulating levels of Hipk in this background
influence both size and number of ectopic eyes induced. Additionally, clonal analysis with loss of
hipk
has revealed altered transcriptional and protein levels
for the RD components toy, ey, so, and eya suggesting Hipk has the ability to modulate the levels and likely the activity of the RDGN. With further studies,
we aim to mechanistically describe
hipk’s
role in eye specification and its involvement with the RDGN.
705C
Study the functions of eye selector genes in Drosophila eye-antenna disc primordium.
Hui-Yu Ku
1,2
, Henry Sun
1,2
. 1) Institute of Molecular
Biology,Academia Sinica, Taipei, Taiwan; 2) Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei,
Taiwan.
The origin of Drosophila compound eyes can be traced back at embryonic stage as eye-antenna disc primordium (EADP), a pair of epithelium-derived sacs
posterior to the dorsal pouch. Clonal and histological analysis suggest that these EADP cells stop motisis since 12 hr embryo, and resumed cell division at
late first instar larval (L1) stage to generate the eye-antennal imaginal disc. The eye-antennal discs then contribute to the compound eyes, antennae, ocelli,
maxillary palps and head cuticle through morphogenesis. Mitotic clonal analysis suggested that the eye and antenna fates do not segregate till second instar
(L2). Interestingly, a number of important transcription factors are expressed in EADP. These include the four Pax genes
eyeless (ey)
,
twin of eyeless (toy)
,
eye gone (eyg)
and
twin of eyg (toe)
.
ey
and
toy
are selector genes to determine the eye fate, while
eyg
and
toe
control cell proliferation in eye disc. Although
these genes play important roles in eye development after L2, their mutations do not affect EADP development, indicating that they might function
redundantly in EADP. Transient knockdown/inactivation (using an early eyg enhancer) of all of them from embryonic to L1 caused headless (21%) and no
eye (26%) phenotypes. We will dissect whether these genes play roles in eye field specification and/or promote proliferation at early eye development stage.
706A
Alleles of
CK2
and
EGFR
modulate the neural defects of
Nspl
and
E(spl)D
.
Adam Majot, Mohna Bandyopadhyay, Christa Bryan, Bhaskar Kahali,
Clifton Bishop, Ashok Bidwai. Biology, West Virginia University, Morgantown, WV.
Dynamic expression of Atonal (Ato) marks the onset of retinal neurogenesis. During this process single R8s are selected from Ato-positive pre-R8 clusters.
Specifically, the bHLH repressors encoded by the
Enhancer of split complex
(
E(spl)C
) inhibit Ato activity in all but the future R8 cell. However, ectopic
E(spl)-M8 fails to repress Ato and R8 patterning is unaffected. In contrast, the dominant
m8
allele
E(spl)D
strongly represses Ato and R8 fate. This mutation
encodes truncated M8 that lacks co-repressor binding and consensus sites for phosphorylation by CK2 and MAPK.
E(spl)D
in combination with the
sensitized
Nspl
allele potently inhibits Ato and the R8 fate to block eye development, suggesting that full-length M8 is likely to be subject to post-
translational modification. However, direct genetic evidence for these kinases has not been forthcoming, as they are haplosufficient and when fully removed
are cell lethal. We reasoned that the synergy between
Nspl
and
E(spl)D
should yield a phenotype sensitive to modulation. Indeed, the CK2-DN allele
Timekeeper
(
Tik
) strongly rescues the reduced eye and R8 defects, providing direct genetic evidence for a role for this kinase. The eye and R8 defects of a
CK2-hypomorphic allele also appear consistent with such a role. We have also tested
egfrf24
, a null allele, in the
Nspl/+; E(spl)D/+
background through
analysis of adult phenotypes and staining of eye discs. Consistent with a role in M8 activation, decreased EGFR dosage rescues the reduced eye and R8
defects. As
egfrf24
does not modulate
Nspl
, rescue may reflect hypo-phosphorylation of wild type M8 encoded by the
E(spl)+
allele. A similar case would
apply to
Tik
. Additionally, we have used clonal analysis of EGFR and
ato
enhancer-LacZ reporters to further understand repression by M8. Our findings are
consistent with the proposal that some levels of EGFR signaling are necessary for lateral inhibition to occur.
707B
Functional analysis of Abd-B protein.
Jesús R. Curt
1
, Nagraj Sambrani
2
, Samir Merabet
2
, Ernesto Sánchez-Herrero
1
, Yacine Graba
2
. 1) Centro de Biología
Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma de Madrid, Nicolás Cabrera 1, Cantoblanco, Madrid, Spain; 2) Institut de Biologie du
Développement de Marseille Luminy, CNRS, Université de la Mèditerranée, Marseille, France.
The Hox genes are a group of genes that determine distinct structures along the anteroposterior axis of bilaterians. They encode proteins containing a
DNA-binding domain, the homeodomain, and act as transcription factors, regulating downstream genes. In Drosophila, the Abdominal-B (Abd-B) Hox gene
is required for the formation of the posterior abdominal segments and the genitalia. When paralog Hox proteins sequences are compared, some conserved
residues and domains are observed. To analyze the function of these conserved aminoacids we have modified the Drosophila Abd-B Hox protein and study
the effect of these changes. The modifications concern residues with unknown function, presumptive interaction domains with the cofactor Extradenticle,
residues that contact the DNA, and homeodomain swaps with other Hox proteins. The functionality of these modifications were assessed both in the embryo
and in the adult. In the embryo, we tested the induction of posterior spiracles by expressing ectopically the modified proteins with the Gal4/ UAS method. In
adults, we tested the repression of the seventh abdominal segment in males and the formation of the female genitalia by expressing the modified proteins
also with the Gal4/UAS method, but in an Abd-B mutant background. Our results allow drawing a map of Abd-B domain requirements for embryonic and
adult functions and identify the context-dependent use of protein domains as a salient feature of AbdB activity. The work also highlights functional
differences in the mode of action of AbdB when compared to anterior Hox proteins.
708C
A missense allele in the evolutionarily-conserved octapeptide motif of Sex combs reduced, a Drosophila Homeotic selector gene, represents the first
of a novel class of mutant alleles.
Lovesha Sivanantharajah, Anthony Percival-Smith. Dept. of Biology, The University of Western Ontario, London,