Congress Abstracts - Society for Developmental Biology

surface of the embryo. In zebrafish, embryo precursor cells known as deep cells (DCs) spread between the Yolk Syncytial Layer and
the overlying surface epithelium (Enveloping layer, EVL) by mechanisms that are still poorly understood. It has been proposed that
radial cell intercalation (RCI) drives tissue spreading during DC epiboly. However, DC epiboly and RCI both require E-cadherin
mediated adhesion and it is thus possible that RCI is solely a manifestation of a different mechanism of tissue spreading mediated by
E-cadherin. Direct assessment of this issue in classical fish models such as zebrafish has been precluded due to the relative high cell
density and concomitance of epiboly with other massive cell movements such as gastrulation and convergent extension. Here we
report a novel teleost model that offers key advantages for the mechanistic analysis of DC epiboly in vivo. In contrast to zebrafish,
epiboly in the annual killifish Austrolebias nigrippinnis occurs in a context of low cell density that precludes RCI, and is temporally
dissociated from the cell movements of gastrulation and convergent extension. We found that spreading of DCs during epiboly uses a
piggy-back mechanism in the absence of RCL, whereby DCs are passively carried on the surface of the moving EVL due to E-
cadherin cell-cell adhesive interactions established between these two cellular domains during epiboly. Sponsors : FONDECYT
(1120558, 1120579), Scientific Millennium Initiative (P09-015-F).
Program/Abstract # 56
Dorsal migration and formation of the secondary chain of sympathetic ganglia
Paul M. Kulesa (Stowers, USA); Frances Lefcort (Montana St U, USA); Jennifer C. Kasemeier-Kulesa, (Stowers, USA)
The sympathetic nervous system plays a vital role in the vertebrate organism to regulate involuntary, autonomic functions including
breathing and heart rate. Sympathetic ganglia (SG), derived from the neural crest, are discrete structures that form in a beautiful
repeating pattern along the vertebrate axis. Previously, we have shown that chemokine signals drive a subpopulation of trunk neural
crest cells to the dorsal aorta and separate mechanisms shape the cells into discrete primary SG. Within hours of their formation,
sympathetic precursors within the primary SG migrate dorsally towards the ventral surface of the dorsal root ganglia (DRG) and form
the permanent, secondary chain of SG. The cellular and molecular mechanisms that mediate dorsal migration and formation of the
secondary SG are largely unknown, due to the ventral, less accessible location of this morphogenetic event deep within the embryo.
Using transverse slice culture and confocal time-lapse microscopy, we detail the events involved in secondary SG formation.
Interestingly, the primary SG move as a cohesive cluster during their dorsal migration. We show extensive cell-cell contacts among
SG cells and long filopodial extensions that extend to contact the forming spinal nerve. Extensions from the spinal nerve interact with
dorsally migrating SG cells. Tissue studies indicate that when the spinal nerve is ablated or re-located, proper dorsal migration is
disrupted. These data indicate extensive cell-cell and cell-microenvironmental interactions are important for proper SG positioning
and development.
Program/Abstract # 57
Regulation of cell migration during dorsal appendage morphogenesis
Sandra Zimmerman, Celeste Berg (U Washington, USA)
Cell motility is critical for development and homeostasis. Abnormalities in these processes can produce birth defects or drive cancercell
metastasis. An excellent model for studying the regulation of cell migration is dorsal appendage (DA) morphogenesis in the
Drosophila ovary. Two patches of somatic follicle cells that lie dorsal to the oocyte form the DAs by reorganizing into tubes and
crawling over the adjacent, squamous, “stretch” follicle cells. We established that DA-cell migration requires both intrinsic and
extrinsic inputs from DA cells and stretch cells respectively. The Sox transcription factor, Bullwinkle (BWK), functions in the nurse
cells to regulate DA-cell migration extrinsically, acting through the tyrosine kinases SHARK and SRC42A in the overlying stretch
cells. Mutations in bwk lead to DA-cell-adhesion defects, aberrant cell migration, and moose-antler-like DAs. To discover how the
BWK-SHARK-SRC42A pathway extrinsically regulates DA-cell migration via the stretch cells, we adapted an established magneticbead
cell separation protocol for a novel application: mass spectrometry. We purified stretch cells from wild-type vs. bwk egg
chambers, compared relative protein expression and phosphorylation, and identified >100 proteins with at least a 2-fold difference in
relative abundance, including known cytoskeletal regulators and growth factors. To discern which of these proteins regulate DA-cell
migration, we are employing protein and RNA expression analysis, tissue-specific RNAi, and clonal analysis. This approach will
identify new factors that regulate DA-cell migration in BWK-SHARK- SRC42A pathway and advance our understanding of how
extrinsic signals contribute to coordinated cell migration.
Program/Abstract # 58
p-53 related protein kinase (PRPK) is required for lamellipodia formation and proper cell shape maintenance in Drosophila
hemocytes
Alvaro Glavic, Vicente Cataldo (U Chile, Chile)
Actin cytoskeleton dynamics is the major determinant of membrane behavior during migration. Dynamic protrusions, specifically
lamellipodia and filopodia, are essential for the migration of motile cells. PRPK (p-53 related protein kinase) is an atypical and
conserved serine/threonine kinase present from Archaea to humans. In yeast, PRPK (Bud32) has been shown to be part of the KEOPS
complex and its mutant displays budding and growth phenotypes. Our previous work showed that Drosophila PRPK is necessary for
PI3K/TOR dependent cell growth and proliferation. Here we describe the role of PRPK in lamellipodia formation and cell
morphology in hemocytes, Drosophila macrophage-like cells. Using the Gal4/UAS system to express a PRPK tag version revealed its
preferential localization at early endosomes. In addition, we found that silencing of PRPK produces hemocytes with abnormal stellate
17