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Poster Full Abstracts - Pattern Formation
Poster board number is above title. The first author is the presenter
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regulation of EGFR signaling in mesoderm alters the number of neuroendocrine precursor cells. However, unlike Daughterless homodimer, activation EGFR
signaling in trunk mesoderm does not induce ectopic neuroendocrine cell fate, suggesting that EGFR signaling is not required for the specification of
neuroendocrine cells but rather for regulating the number of neuroendocrine precursor cells.
701B
Conserved MAPK and CK2 sites in E(spl)-M8 regulate repression of Atonal.
Mohna Bandyopadhyay, Adam Majot, Bhaskar Kahali, Clifton Bishop,
Ashok Bidwai. Biology, West Virginia University, Morgantown, WV.
Inhibitory Notch signaling is required for patterning the founding R8 cells in the developing retina, during which Atonal (Ato) activity is antagonized by
the E(spl) repressors. This antagonism requires phosphorylation of E(spl)-M8 by CK2, which appears to be necessary but not sufficient for repression of
Ato. The presence of a highly conserved consensus site for MAPK proximal to the CK2 site raised the possibility that multi-site phosphorylation controls
M8 activity. MAPK mediates the effects of Epidermal Growth Factor Receptor (EGFR) signaling, and previous studies have shown that excess R8s are
specified upon loss of
egfr
or its pathway components. We sought to determine if the MAPK site in M8 is functional, and if it is dependent on modification
at the CK2 site. Using site-specific variants of M8, we find that both the CK2 and MAPK sites are necessary for repression of Ato, and that CK2 is epistatic.
Accordingly, halved dosage of
egfr
strongly mitigates repression of Ato by a CK2 phosphomimetic variant, indicating that EGFR signaling may impinge on
M8, itself. The CK2 site (SDCD) appears to serve as a gatekeeper, as its deletion activates M8 repression of Ato, albeit with a strength that is attenuated
when compared to that of the CK2+MAPK mimic. We have also used Gal4 drivers specific for different stages of the morphogenetic furrow (MF) to
evaluate when and where repressor activity manifests. Our findings reveal that M8 activation is likely to occur at stage-2/3 of the MF where active MAPK is
present and where R8 selection normally occurs. Accordingly, when both CK2 and MAPK sites are replaced with Asp residues inappropriate repression of
Ato manifests even at stage-1, where Ato auto-regulation normally occurs. This auto-regulation is important to drive Ato levels to attain a threshold
sufficient for the R8 fate. The possibility arises that activation of M8 by multi-site phosphorylation at stage-2/3 acts as a spatial switch that permits Ato
repression only after the pre-R8s are formed.
702C
A Novel function of Muscle Myosin II in Drosophila melanogaster Eye Development.
Carlos Cano, Landry E. Nfonsam, Jennifer Curtiss. Biology, New
Mexico State University, Las Cruces, NM.
Drosophila Mhc encodes the heavy chain of the conventional (muscle) myosin II motor protein, which is important for skeletal muscle function.
Nonconventional myosin II family members (e.g. Zipper) have well-known roles in cytokinesis and migration of non-muscle cells. However, recent studies
show that Mhc is required for cell migration in two non-muscle contexts in Drosophila melanogaster: in the development of the air sac primordium during
tracheal development and in border cell migration during oogenesis. Based on a transcriptomic screen we performed to identify novel eye genes, Mhc is
highly expressed in eye tissues. Here, we report a novel role for Mhc in development of the Drosophila eye. We used the FLP/FRT system to generate
homozygous clones of the loss-of-function Mhc2L2881 allele. Mhc2L2881 adult mosaic eyes showed strong effects on eye development, including gaps and
disruptions in the ommatidial array, loss of photoreceptors and abnormal formation of rhabdomeres. Antibody stainings using anti-DE-Cadherin revealed
that the cells that lie between photoreceptor clusters in Mhc2L2881 mosaic eye discs were more irregular in shape and their adherens junctions appeared to
be enriched on one side rather than being evenly distributed. We also observed occasional loss of cone cells and photoreceptors in Mhc2L2881 mutant
clones, notably the R8 precursors, which are the founding cells of each ommatidium. We found that R8 precursors could still develop in Mhc2L2881
homozygous tissue and in some cases were able to recruit other photoreceptors. However, Mhc2L2881 R8 photoreceptor nuclei were often located more
basally within the eye-antennal disc epithelium compared to surrounding wild-type nuclei. These results suggest that Mhc regulates cell morphology and/or
cell-cell adhesion during eye development. The stochastic loss of ommatidial cells likely results from failure of signaling between cells that are not well
integrated into the epithelium, or from cell death. In conclusion, muscle myosin II has an effect on eye cell morphology, which in turn affects cell fate
specification.
703A
Novel function of the kinase Nemo in the negative regulation of Atonal expression in the
Drosophila
eye.
Vilaiwan Fernandes, Esther Verheyen.
Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia.
The high degree of organization of the
Drosophila
compound eye originates during patterning and morphogenesis of the third larval instar eye imaginal
disc. Patterning of the eye is a reiterative process in which a regular lattice of R8 photoreceptors is specified one column at a time posterior to the furrow.
Central to this process is the expression and refinement of the bHLH proneural transcription factor Atonal (Ato). Here, we describe a novel role for the
kinase Nemo (Nmo) during Ato refinement and R8 spacing. Discs mutant for
nmo
revealed defects in Ato refinement, such that Ato expression fails to refine
into intermediate groups (IGs) resulting in frequent R8 doublets. Conversely, overexpression of
nmo
in flipout clones results in loss of IGs and greater
spacing between individual R8s, suggestive of a role for Nmo during the stage of R8 lateral inhibition. Notch and EGFR signalling are highly conserved
pathways; both of which are known to promote R8 refinement. Using clonal analysis we tested whether expression of targets of either of these pathways are
affected by loss of
nmo
. Intriguingly, we find that loss or reduction of
nmo
results in reduced expression of the Notch targets, Enhancer of split and
Daughterless, as well as the EGFR targets, Rough and
pointed P1
. Additionally, we find that levels of the EGFR effector pMAPK are reduced in the absence
of
nmo
. Collectively, our data suggest positive roles for Nmo in both Notch and EGFR signalling during eye development. We aim to determine whether
Nmo’s effect on Ato refinement stems from its regulation of one or both of these signalling pathways. Our study will provide further insight into the
complex regulation of Ato expression in the developing retina, a process that has many parallels throughout neural fate specification.
704B
Homeodomain-interacting protein kinase interacts with the retinal determination gene network and is required for development of the
Drosophila
compound eye.
Jessica A Gardner
1
, Wendy Lee
2
, Esther Verheyen
1
. 1) Molecular Biology and Biochemistry, Simon Fraser University, Burnaby B.C., B.C,
Canada; 2) Dept. Cell Biology, Harvard, Boston, MA, USA.
The
Drosophila
eye-antennal imaginal disc is an excellent system for studying tissue growth, cell-specification, patterning and signal transduction