Abstracts - Society for Developmental Biology

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trafficking of cargo proteins and does not affect primary cilia formation. Here we show that expression of dominant
negative (DN) versions of KIF17 perturbs GLI2 and GLI3ciliary localization. Surprisingly, expression of DNKIF17 in cell
signaling assays and in chick neural tubes does not alter HH-dependent cell signaling orventral neural tube patterning.
These data suggest that ciliary accumulation of GLI proteins is not essential for HH signaling.
Program/Abstract # 307
Negative regulation of Epidermal Growth Factor Receptor signalling in the Drosophila ovary
De Vito, Scott, McGill University, Montreal, Canada; Biosclair Lachance, Jean-François (Chicago, U.S.A.); Fregoso
Lomas, Mariana (Montreal, PQ, Canada); Nilson, Laura (Montreal, Canada)
During oogenesis the follicular epithelium is patterned to form the structures of 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 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
regulators, D-cbl, which functions as an E3 ubiquitin ligase for EGFR, and Gap1, which promotes the inactivation of Ras.
We show that loss of D-cbl in follicle cells results in expansion of dorsal fates onto the ventral side of the follicular
epithelium. Additionally, these clones display a shortening of dorsal fates along the AP axis. We also show that loss of
Gap1 results in the expansion of dorsal fates ventrally but fails to display any shortening of dorsal fates along the AP axis,
suggesting that the function of Gap1 is distinct from that of D-cbl and Sty. We also looked at the regulation of a
downstream factor, Capicua, as a readout of EGFR activity. Interestingly, the pattern of EGFR-mediated changes in
Capicua localization is expanded in D-cbl and Gap1 mutant clones along both the AP and DV axes. This AP expansion is
therefore inconsistent with the observed decrease in dorsal fates.
Program/Abstract # 308
The Tbox-20 transcription factors Midline and H15 function as localized negative regulators of epidermal growth
factor receptor signaling output
Fregoso Lomas, Mariana; Hails, Fiona (McGill, Canada); Boisclair Lachance, Jean-François (Chicago); Nilson, Laura
(McGill, Canada)
We use the Drosophila ovarian follicular epithelium to study signaling pathways and patterning during development. This
epithelium secretes the egg shell, including the two dorsal appendages derived from the dorsal anterior primordia. These
primordia can be recognized through the high expression of the Broad-Complex (Broad) transcription factor, and are
separated by a region of cells at the dorsal midline that do not express Broad. Outside of this region, all follicle cells
express basal Broad. Dorsally-localized EGF signalling coming from the underlying oocyte initiates this spatial pattern
along the dorsal-ventral axis, but the signals that pattern the anterior-posterior (AP) axis are less well understood. To better
understand AP patterning, we characterized a new locus called F27 required for this process. In F27 mutant epithelia, the
posterior limit of the high Broad expression domain is extended, suggesting that dorsal anterior fates have been determined
more posteriorly. We also show that wild type posterior follicle cells are refractory to ectopic EGFR activity, but that F27
mutant epithelia respond to ectopic activation of the EGFR signalling cascade by adopting dorsal anterior fates. We
mapped the F27 mutation to the midline (mid) gene, which encodes a Tbox transcription factor. Mid is expressed in the
posterior follicular epithelium, and ectopic expression of Mid in the dorsal anterior domain represses dorsal fates. We
found that the Mid paralog H15 participates in this process as well. Our data show that these factors regulate posterior fate
in the follicular epithelium, and are acting as novel negative regulators of EGFR signalling output.
Program/Abstract # 309
Cdx1 and Cdx2 have context dependent functional specificity in the intestine
Grainger, Stephanie L.; Hryniuk, Alexa; Lohnes, David,University of Ottawa, Ottawa, Canada)
The caudal related homeodomain transcription factors Cdx1 and Cdx2 are expressed in the developing endoderm,
persisting into adulthood. Cdx1-/-mutants are viable and fertile and display no overt phenotype in the intestine, while
conditional mutation methods have revealed that Cdx2 is required for patterning the intestinal epithelium and specification
of the colon. During adult homeostasis of the intestinal tract, Cdx1 appears to functionally overlap with Cdx2 in the more
distal regions of the intestinal tract, as Cdx1/2 double mutants have a stronger anterior transformation of the distal colon
than Cdx2 mutants; however, Cdx1 seems to be dispensable during small intestinal patterning and differentiation. Cdx1
and Cdx2 are differentially expressed in the intestinal epithelium. While both are expressed in a posterior-high gradient,