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Poster Full Abstracts - Cell Biology and Signal Transduction
Poster board number is above title. The first author is the presenter
177
Epithelial cell polarity in the hindgut of the
Drosophila
embryo.
Alexandra Kumichel, Elisabeth Knust. Max Planck Institute of Molecular Cell Biology
and Genetics, Pfotenhauerstr. 108, Dresden, Germany.
The Crumbs complex, which consists of the core components Crumbs (Crb), Stardust,
D
Patj and
D
Lin-7, is localized in the subapical region of
ectodermally derived epithelial cells, apical to the zonula adherens (ZA), where it is essential for the maintenance of apico-basal cell polarity. In the
Drosophila
embryonic hindgut epithelium, the large intestine is subdivided into a dorsal and a ventral domain, which are separated by two lateral cell rows
called boundary cells. Boundary cells differ in their shape and organization of the apical surface from the remaining hindgut cells. Strikingly,
crb
mRNA and
protein levels are strongly upregulated in these cells in comparison to the other cells of the hindgut, and both are localized apically. In order to investigate the
role of Crb in the altered phenotype of the boundary cells, we studied the localization of the other core components of the Crb complex in the boundary cells
by immunohistochemistry and found that none of them showed upregulated protein levels or an altered localization compared to the cells of the dorsal or
ventral domain. We also studied the localization of other polarity markers as well as the effect of loss or overexpression of Crb on cell morphology of the
boundary cells.
162C
Drosophila Planar Polarity Gene Multiple Wing Hairs Interacts with formin to Locally Inhibit Actin Cytoskeleton.
Qiuheng Lu, Paul Adler.
University of Virginia, Charlottesville, VA.
The frizzled pathway has been extensively studied in wing planar cell polarity (PCP); however, it remains unclear how the PCP signal is read out as single
distally pointing actin-rich hair. The downstream PCP gene multiple wing hairs (mwh) is thought to encode an inhibitor of the actin cytoskeleton. The amino
half of Mwh shows similarity to the same region of Diaphanous (dia), a protein that promotes actin polymerization. The amino terminal part of Dia is key for
regulating Dia activity and it also mediates dimerization. This suggested the possibility that Mwh might inhibit the activity of the actin cytoskeleton by
acting as a “dominant negative Dia” (i.e. by forming inactive heterodimers). Consistent with this model we found that expression of a constitutively active
Dia leads to multiple hair cells. We have also found genetic interactions between mwh and dia, between the amino half of Mwh and dia, as well as between
Mwh and constitutively active Dia that are consistent with the two proteins acting antagonistically. Further we established that the two proteins could be co-
immunoprecipitated from wing discs and that they colocalized in pupal wing cells. Further studies of this model are in progress.
163A
Separating planar cell polarity and Hippo signaling activities of the protocadherins Fat and Dachsous.
Hitoshi Matakatsu, Seth Blair. Dept Zoology,
Univ Wisconsin, Madison, WI.
The protocadherins Fat (Ft) and Dachsous (Ds) are required for several biological processes in the development of
Drosophila
, including controlling
growth via the Hippo signaling pathway, planar cell polarity (PCP) and the proximodistal patterning of appendages like as wing and eye. Recently it has
been suggested that mammalian homologue Ft and Ds also regulates PCP and growth. Ft and Ds binds in a preferentially heterophilic fashion. It has thus
been suggested that Ft and Ds serve not as adhesion molecules, but as receptor and ligand in a poorly understood signaling pathway. To understand Ds-Ft
signaling pathway on PCP and growth control, we performed a structure-function analysis of Ft and Ds, separating their adhesive and signaling functions.
We found that the extracellular domain of Ft is not required for its activity in growth control, PCP and proximodistal patterning (Matakatsu and Blair, 2006).
To identify the domains which are responsible for PCP and growth control activities in Ft’ intracellular domains (ICD), we extend analysis for Ft’ ICD.
Surprisingly, the effects of Ft’ICD on PCP and the growth control are largely separable, suggesting that PCP and growth control is mostly independent
pathway. In contrast with Ft, the extracellular domain of Ds is necessary and sufficient to mediate its effects on PCP, consistent with the model that Ds acts
as a ligand during PCP. However, we would provide evidence that Ds can regulate growth independently of Ft, and that the intracellular domain of Ds can
affect growth control and proximodistal patterning.
164B
Short stop in rhabdomere terminal web is essential for Drosophila photoreceptor morphogenesis.
Sang-Chul Nam, Uyen Ngoc Mui, Christina M.
Lubczyk. Dept Biol, Baylor Univ, Waco, TX.
Crumbs (Crb), a cell polarity gene, has been shown to provide a positional cue for the apical membrane domain and adherens junction (AJ) during
Drosophila photoreceptor morphogenesis. It has recently been found that stable microtubules in developing Drosophila photoreceptors were linked to Crb
localization. Coordinated interactions between microtubule and actin cytoskeletons are involved in many polarized cellular processes. Since Spectraplakin
(Short stop, Shot) is able to bind both microtubule and actin cytoskeletons, the role of Shot was analyzed in the regulations of apical Crb domain in
developing Drosophila photoreceptors. The localization pattern of Shot in developing pupal photoreceptors showed a unique intracellular distribution. Shot
localized at rhabdomere terminal web which is at the basal side of the apical Crb or rhabdomere, and in between the AJs. The shot mutant photoreceptors
showed dramatic mislocalizations of Crb, AJs, and the stable microtubules. This role of Shot in Crb and AJ regulation was further supported by Shot’s gain-
of-function phenotype. Shot overexpression in photoreceptors caused a cell polarity defect including dramatic mislocalization of Crb, AJs and the stable
microtubules in the developing photoreceptors. Furthermore, a strong genetic interaction between shot and crb was found using a genetic modifier test. In
summary, we found a unique localization of Shot in photoreceptors, and identified the role of Shot in the regulation of the apical Crb domain and AJs
through genetic mutational analysis. Our data suggest that Shot, an actin-microtubule cross-linker, is essential in the apical and AJ controls during the
photoreceptors morphogenesis.
165C
Impact of retinal disease-causing missense mutations in the extracellular domain of Crumbs on photoreceptor development and survival in
Drosophila
.
Milena Pellikka, Ulrich Tepass. Dept Cell & Systems Biology, University of Toronto, Toronto, ON.
The apical transmembrane protein Crumbs (Crb) is a critical regulator of epithelial polarity and apical membrane morphogenesis in photoreceptor cells
(PRCs).
Drosophila
and vertebrate Crb proteins localize to corresponding apical membrane domains, the stalk membrane in
Drosophila
and the inner
segment of vertebrate PRCs. Crb is required for the maintenance of rhabdomere shape, zonula adherens integrity, stalk membrane length, and cell survival of
Drosophila
PRCs. Similarly, mutations in one of the three human orthologs of Crb (CRB1) are linked to eye degenerative conditions such as Leber’s