Congress Abstracts - Society for Developmental Biology

medaka genome. These miRs are encoded as six different genes organized into three bi-gene clusters. RT-PCR and in situ
hybridization (ISH) showed that these miRs are specifically transcribed as continuous precursor RNA molecules in the skeletal muscle
during embryogenesis. ISH using LNA-modified oligoprobes showed that 22-nt mature miR molecules accumulate in the trunk
skeletal muscle. miR-206 and miR-133 were also expressed in the precursor cells of the pectoral fin muscles, in which miR-1 was not
detected. Moreover, inhibition of miR-206 function using antisense morpholino oligonucleotide disrupted skeletal muscle formation,
especially in the pectoral fin muscle. These results suggest that medaka miR-206 might play important roles in the pectoral fin
myogenesis. We are currently analyzing expression of muscle-related transcription factors, MyoD, Myf5, Pax3, Pax7 and Lbx, which
are potential molecular players in the pectoral fin myogenesis in medaka. Our study would provide insights into the gene regulation in
skeletal muscle formation both at the transcriptional and posttranscriptional levels.
Program/Abstract # 234
GTPase control of blood vessel morphogenesis
Cleaver, Ondine B.; Koo, Yeon (UT Southwestern Medical Center, USA); Xu, Ke (Harvard University, USA); Davis, George
(University of Missouri, USA)
Cardiovascular function depends on the formation of blood vessels by endothelial cells (ECs). However the cellular and molecular
mechanisms that coordinate to drive this process are only beginning to be unraveled. We carried transcriptional screening of
embryonic blood vessel endothelium and found enrichment of a family of EC-specific effectors of the GTPases Rho, Rac, Rap and
Cdc42. We recently demonstrated the requirement for a novel GTPase-interacting protein called Rasip1, and its binding partner the
RhoGAP, Arhgap29, for endothelial tubulogenesis. Rasip1 null mice display aberrant localization of junctional complexes, and loss of
adhesion to extracellular matrix, resulting in failure of functional blood vessels. Depletion of either Rasip1 or Arhgap29 in cultured
HUVECs caused increased RhoA/Rock/Myosin II activity, suggesting that Rasip1 and Arhgap29 function together to suppress RhoAdependent
internal contractility. In addition, both Cdc42 and Rac1 activity were dramatically downregulated in siRasip1/siArhgap29
treated cells. Here, we dissect the functional domains required for Rasip1 function and show its control of cell adhesion via regulation
of endocytosis. Current studies are aimed at elucidating the mechanisms by which GTPases drive basic cellular behaviors that
culminate in blood vessel formation.
Program/Abstract # 235
MED23, a subunit of the global transcription complex, Mediator is essential for vascular remodeling and regulation of WNT
signaling during cranial ganglia formation
Bhatt, Shachi, (Stowers Institute for Medical Research, USA), Sandell, Lisa (Louisville, KY, USA); Youngwook, Ahn; Krumlauf, Robb;
Trainor, Paul (Stowers Institute for Medical Research, USA)
A close physical relationship between nerves and blood vessels is crucial for proper neuro-vascular function. Thus, it is not surprising
that nerves and blood vessels share molecular and cellular signals during development. Here we describe the mouse mutant, snouty,
obtained from a forward genetics screen which exhibits defects in vascular remodeling and cranial sensory neuron formation. These
neuro-vascular defects result in embryonic lethality. snouty carries a point mutation in med23, a ubiquitously expressed subunit of
transcription co-factor, Mediator. Detailed analyses reveal that loss of med23 disrupts multiple steps of cranial placode formation,
which leads to defects in cranial sensory neurons and ganglia development. Interestingly, these placodal defects are associated with
elevated levels of WNT signaling and genetic suppression of WNT signaling partially restores cranial ganglionic neuron
differentiation. Vascular remodeling defects in snouty embryos are associated with elevated levels of vegfa and defects in endothelial
cell-cell adhesion as observed by fewer tight junctions. snouty, thus represents a unique mouse model for investigating the link
between global gene transcription and spatio-temporal signaling during embryogenesis. Our findings suggest a novel role for
transcription co-factor MED23 in vascular and neural development and highlight a surprising link between the MED23 containing
Mediator complex and WNT signaling in regulation of neuro-vascular development.
Program/Abstract # 236
Endoderm convergence controls myocardial migration
Lin, Fang; Ye, Ding (The University of Iowa, USA)
In vertebrates, heart formation requires the migration of bilateral myocardial precursors to the midline, where they form the primitive
heart tube. The adjacent endoderm is critical for this migration, but the underlying mechanisms remain unclear. Myocardial migration
in zebrafish requires signaling mediated by sphingosine-1-phosphate (S1P) and its cognate G protein-coupled receptor, S1pr2. Our
recently published data revealed that S1pr2 signals through a Gα 13 /RhoA-dependent pathway to control convergent movement of the
endoderm, and that this in turn promotes myocardial migration. We have used transgenic lines in which endodermal and myocardial
cells are labelled with distinct fluorescent proteins at early developmental stages to determine how endoderm convergence controls
myocardial migration. Our analysis revealed complex and dynamic associations between the myocardial and the endoderm during
their migration. The endoderm rapidly converged towards the midline through the 14 somite stage (14s), at which point this migration
slowed to a minium. In contrast, the myocardial cells underwent three distinct steps of migration: 1) before 14s, they migrated toward
the midline with the endoderm, from a position dorsal to the endoderm; 2) at 14s, they migrated to the ventral side of the endodermal
layer (translocation); and 3) after 14s, they migrated toward the midline beneath the endoderm. Our results suggest myocardial cells
migrated by two distinct modes: first by passive migration that depends on endoderm convergence, and then by active migration that
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