Congress Abstracts - Society for Developmental Biology

Program/Abstract # 323
Drosophila glypicans Dally and Dally-like are essential regulators for JAK/STAT signaling and Unpaired distribution in eye
development
Lin, Xinhua (Cincinnati Children's Hospital, USA); Zhang, Yan (Chinese Academy of Sciences, China); You, Jia (Cincinnati
Children’s Hospital, USA); Ren, Wenyan (Chinese Academy of Science, China)
The highly conserved janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is a well-known signaling
system that is involved in many biological processes. In Drosophila, this signaling cascade is activated by ligands of the Unpaired
(Upd) family. Therefore, the regulation of Upd distribution is one of the key issues in controlling the JAK/STAT signaling activity and
function. Heparan sulfate proteoglycans (HSPGs) are macromolecules that regulate the distribution of many ligand proteins including
Wingless, Hedgehog and Decapentaplegic (Dpp). Here we show that during Drosophila eye development, HSPGs are also required in
normal Upd distribution and JAK/STAT signaling activity. Loss of HSPG biosynthesis enzyme Brother of tout-velu (Botv),
Sulfateless (Sfl), or glypicans Division abnormally delayed (Dally) and Dally-like protein (Dlp) led to reduced levels of extracellular
Upd and reduction in JAK/STAT signaling activity. Overexpression of dally resulted in the accumulation of Upd and up-regulation of
the signaling activity. Luciferase assay also showed that Dally promotes JAK/STAT signaling activity, and is dependent on its heparin
sulfate chains. These data suggest that Dally and Dlp are essential for Upd distribution and JAK/STAT signaling activity.
Program/Abstract # 324
The zebrafish diencephalic glial bridge is made up of a heterogeneous population of astroglial cells
Zaman, Paula; Velez, Carla; Bashiruddin, Sarah; Dimova, Kalina; Alligood, Kristin; Doris, Rosemarie; Sinha, Risha; Husain,
Tanya; Mahlanza, Tatenda; Devoto, Stephen; Barresi, Michael (Smith College, USA)
In the developing Zebrafish brain, axons are guided across the midline by attractant and repellent protein cues to form commissures.
The postoptic commissure (POC) of the diencephalon is the first forming commissure in the zebrafish brain. POC axons contact a
group of astroglial cells that express Glial fibrillary acidic protein, (Gfap) and form what has been called the “Diencehphalic Glial
Bridge”. The temporal and spatial association of POC axons with these astroglial cells suggests this glial bridge may serve to provide
a supportive substrate for axonal growth across the midline. However, little is known about the molecular and cellular characteristics
that define these astroglial cells. We have combined embryological, transgenic and molecular analyses to characterize the cells that
make up the diencephalic glial bridge in zebrafish. Using transgenic lines that express cytoplasmic, membrane tethered, or nuclear
localized fluorescent proteins under the Gfap regulatory sequences we have been able to visualize astroglial cells in the zebrafish
forebrain. By employing gastrula staged cell transplantation procedures with these lines, we have been able to describe at least three
distinct Gfap+ cell morphologies. Previously, Trevarrow and colleagues conducted an unbiased screen for antibodies that showed
distinct labeling patterns in the zebrafish brain, and four antibodies were shown to mark radial glial-like cells, and were termed
Zebrafish Radial Fiber 1-4 (Zrf). While Zrf1 has been shown to recognize zebrafish Gfap, the identity of the proteins recognized by
Zrf2-4 are unknown. All four Zrf antibodies exhibit protein labeling that overlaps with the location of the POC. We demonstrate here
that anti-Zrf2 and anti-Zrf3 display similar patterns of expression in the zebrafish forebrain but are distinct from Zrf1 labeling.
Interestingly, anti-Zrf4 shows a restricted expression pattern that overlaps only the area of the glial bridge associated with
commissural axon crossing. We are now conducting experiments that combine our transgenic and cell transplantation approach with
Zrf immunoreactivity to correlate astroglial morphology with Zrf labeling. We are also carrying out biochemical analyses to identify
the proteins recognized by the Zrf2,3,4 antibodies. Our data is building a model that supports the presence of a heterogenous
population of astroglial cells make up the diencephalic glial bridge, which may provide an instructive environment of commissural
midline crossing.
Program/Abstract # 325
Axial specification in mice is controlled by an extra-embryonic Wnt3 signaling event
Rivera-Perez, Jaime A.; Tortelote, Giovane; Huang, Tingting (University of Massachusetts Medical School, USA); Wakamiya, Maki
(The University of Texas-Galveston, USA); Hadjantonakis, Anna-Katerina (Sloan Kettering Institute, USA); Behringer, Richard (M.
D. Anderson Cancer Center, UT-Houston, USA)
Genetic evidence has revealed a fundamental role for the Wnt signaling pathway in the process of axial specification in mice.
However, the question of how the Wnt pathway controls this process remains an open question. Here we provide evidence that axial
specification in mice is the result of a Wnt3-directed inductive event initiated by the posterior visceral endoderm, an extra-embryonic
tissue. We show that Wnt3 signals through the canonical Wnt signaling pathway and suggest that a feedback loop controls the
maintenance of Wnt3 expression in the posterior visceral endoderm allowing gastrulation to proceed. Our results suggest an
evolutionary conserved role of the canonical Wnt signaling pathway in the process of axial specification across vertebrates. However,
since multiple Wnt ligands appear to act as inducers in different vertebrates, it appears that different Wnt ligands have been co-opted
for gastrulation during vertebrate evolution.
Program/Abstract # 326
Wnt5a and Wnt5b function redundantly via noncanonical pathways to extend the embryonic axis
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