Abstracts - Society for Developmental Biology

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Neural crest cells arise in the dorsal neural tube and migrate into the periphery, forming diverse structures including
sensory neurons and much of the craniofacial skeleton. Research into the molecular mechanisms of neural crest migration
has established a gene regulatory network (GRN) of transcription factors that produces cells capable of migration.
However, expression of the transcription factors within the neural crest GRN does not guarantee eventual migration as a
neural crest cell. As previous studies have shown that phosphoregulation is required for migration, regulators of
phosphorylation status may control the acquisition of migratory ability. We have identified a novel phosphoregulator,
Paladin, in a screen for genes upregulated as a late consequence of neural crest induction. Our work has demonstrated that
Paladin acts as an antiphosphatase and is required for normal neural crest migration. To understand how Paladin exerts its
effects, we aimed to define the proteins with which Paladin interacts. We have performed a yeast two-hybrid screen to
identify the targets and binding partners of Paladin in a cDNA library that includes premigratory and migratory stages of
neural crest development. Our screen has revealed novel Paladin protein interactions, including a phosphorylationdependent
interaction with myosin heavy chain 9, a non-muscle motor protein. Experiments to confirm these interactions in
chick neural crest cells are currently underway. Our data identify new candidate regulators of neural crest development and
support a role for Paladin-modulated differential protein activity in regulating neural crest migration. Funding: U of MN
UROP; F32DE019973 and K22DE015309; Minnesota Medical Foundation
Program/Abstract # 369
TashT: A new model for Hirschsprung disease
Toure, Aboubacrine M., UQAM, Montréal, Canada; Bergeron, Karl-F.; Cardinal, Tatiana; Beland, Melanie (UQAM,
Montreal, PQ, Canada); Silversides, David W. (UdeM, St-Hyacinthe, PQ, Canada); Pilon, Nicolas (UQAM, Montreal,
PQ, Canada)
Hirschsprung disease (HSCR) or aganglionic megacolon is a severe congenital anomaly of the enteric nervous system
(ENS) with an incidence of 1/5000 in newborns and a 4:1 male to female sex ratio. This lethal condition is characterized
by a lack of intestinal motility due to the absence of neural ganglia in the terminal region of the gut. The lack of gut
innervation results from improper colonization by enteric neural crest cells (eNCC). The genetics of HSCR is complex,
involving mutations in multiple genes such as members of the RET and EDNRB signaling pathways. However, mutations
in known genes account for only about half of the cases of megacolon observed. Moreover, although environmental factors
are known to affect HSCR pathogenesis, the contribution of such non-genetic factors is poorly understood. TashT is a
novel mouse model that has been generated via an insertional mutation screen for genes involved in NCC development. As
for human HSCR, TashT homozygote pups display megacolon with variable penetrance and a male sex bias (~5:1). We
have localized the transgene insertion site in a 3.3 Mb gene desert on chr.10B2, syntenic to human chr.6q16 and devoid of
HSCR associated gene. TashT homozygote embryos exhibit defective gut colonization by eNCC. This defect is
characterized by a migration delay as well as a reduced number of eNCC; the status of Ret and Ednrb signaling pathways is
currently being evaluated using gut explants. Interestingly, although very few neurons are present in the resulting
aganglionic zone, they are sufficient for colonic motility for most mutants. However, other data suggest that such marked
reduced number of neurons sensitizeTashT homozygotes to exogenous insults affecting neuron survival.
Program/Abstract # 370
Parallel integrin-associated pathways regulate gonadal distal tip cell migration and turning in Caenorhabditis
elegans
Wong, Ming-Ching; Kennedy, William P.; Schwarzbauer, Jean E., Princeton University, Princeton, United States
The U-shaped morphology of the C. elegans hermaphroditic gonad arm relies on the migration of the distal tip cell (DTC).
DTCs first migrate longitudinally away from the midbody along the ventral basement membrane, then turn to migrate
longitudinally backtoward the midbody along the dorsal basement membrane. Our previous work has shown that the
DTC’s turn back toward the midbody relies on integrin-associated Nck-interacting kinase (MIG-15) and MIG-38, a novel
protein. Here, we describe the requirement for a parallel integrin-related pathway identified by analyses of LET-607 and
cbp-1, a transcription factor and coactivator, respectively. DTC-specific RNAi knockdown of either let-607 or cbp-1
resulted in failure to return to the midbody by more than two-thirds of DTCs, resulting in gonad arms that extended to the
pharynx or thetail. Because both let-607 and cbp-1 exert transcriptional control, we took a candidate gene approach to
identify their target genes that have a rolein DTC turning. Curiously, this screen uncovered target genes shared between
LET-607 and CBP-1 that encode integrin adhesion receptors and integrin signaling proteins. In particular, expression of
src-1 and talin, which encode a non-receptor tyrosine kinase and an integrin activator, respectively, depends on LET-607
and CBP-1. Double RNAi knockdown of src-1 and talinphenocopies cbp-1 knockdown, suggesting that these two genes
are mainly responsible for CBP-1-dependent turning. Furthermore, the overexpression of SRC-1 in DTCs restores turning