Congress Abstracts - Society for Developmental Biology

studies in chick and mouse demonstrating that cells near the extreme anterior and posterior poles of the initially flat endoderm
translocate by nearly half the embryo’s length to arrive at their final position in midgut. In the present work, hindgut formation was
observed directly by multi-photon live imaging in the chick embryo. We identified a rapid and collective, polarized movement of
endoderm cells into and through the caudal intestinal portal. These cell movements were intrinsic to the endoderm, and essential for
hindgut formation. We conclude that the collective posterior flux of endoderm cells along the ventral midline drive antero-posterior
folding to form the hindgut, whereby continued addition of cells to the forming hindgut causes a progressive folding into the
elongating tail bud. Finally, we identified FGF signaling as required for these polarized cell movements, and ultimately for involution
of the endoderm to form the hindgut. Work is ongoing to identify the physical forces that drive this process, and how FGF signaling
regulates such forces during early organogenesis of the gut.
Program/Abstract # 189
Gut morphogenesis involves changes in cell shape that require ZFP568 and Hand1
Ulmer, Barbel Maria; Garcia-Garcia, Maria J. (Cornell University, USA)
During early mouse embryogenesis, the elongation and subsequent closure of the definitive endoderm gives rise to the primitive gut
tube. Although these events are essential for the formation of the digestive and respiratory organs, relatively little is known about
cellular and genetic events mediating the closure of the gut tube. We found that the KRAB-domain zinc-finger protein ZFP568 and
the bHLH transcriptional activator Hand1 are required for proper gut morphogenesis. In both Zfp568 chato and Hand1 mutants the
definitive endoderm failed to form a proper foregut and hindgut pocket, did not elongate and did not zip up to close the gut tube. ISH
with markers of early gut morphogenesis, such as Shh, Nepn and hex1, revealed that proper regional specification of the gut endoderm
takes place in Zfp568 chato and Hand1 mutants, but that these populations fail to translocate to form the foregut and hindgut pockets.
We thus hypothesize, that ZFP568 and HAND1 are essential for cell movement and cell shape rather than cell differentiation in the
definitive endoderm. Interestingly, we found that the formation of the foregut and hindgut pockets in wild type embryos correlates
with changes in the shape of endoderm cells from a squamous to a cuboidal morphology. In contrast, endoderm cells remained
squamous in Zfp568 and Hand1 embryos. By studying Zfp568 and Hand1 mutants, we are currently determining the contribution of
these cell shape changes to gut morphogenesis and the underlying molecular mechanisms that control the folding of gut epithelia in
vertebrate organisms.
Program/Abstract # 190
ADAMTS9 is a highly conserved protease crucial for gastrulation, left-right symmetry, neurulation, craniofacial development
and intrauterine growth
Nandadasa, Sumeda; Nelson, Courtney; Somerville, Robert; Apte, Suneel (Cleveland Clinic Lerner Research Institute, USA)
Little is known about extracellular matrix (ECM) remodeling during gastrulation. We investigated the role of a secreted, but cellsurface
bound metalloprotease, ADAMTS9 (A disintegrin and metalloproteinase with thrombospondin motifs 9), known to cleave
ECM proteoglycans, using an allelic series. In mice, a unique cup-shaped structure known as the egg cylinder is formed prior to
gastrulation, comprising two epithelial cell layers, the ectoderm and the visceral endoderm. The basement membrane between them is
remodeled to accommodate the newly formed mesoderm. Adamts9 was expressed at the onset of gastrulation (E 6.5) in distal
ectoderm and the visceral endoderm cells, in the vicinity of the future node. During gastrulation, Adamts9 expressing cells
delaminated from the ectoderm to colonize the newly forming mesoderm. We found that Adamts9 null embryos (-/-) , die around E.7.0
without undergoing gastrulation and showed a disorganized ECM. We used a membrane-targeted, hypomorphic gene trap allele
(Adamts9 gt ), and tissue specific Cre recombinase drivers, Sox-2 cre, TTR-cre, and Brachyury (T)-cre, in combination with a floxed
Adamts9 allele (Adamts9 Fl ) to investigate the functions of Adamts9 in gastrulation and the post-gastrula embryo. Indeed, each of these
mutants extended survival past gastrulation, suggesting a crucial role for membrane-bound ADAMTS9 during gastrulation, and
distally acting secreted protease in late development. We show that ADAMTS9 is crucial for embryo turning, heart tube looping,
neurulation, left-right symmetry, cranio-facial development, melanoblast survival, and for establishing a functional fetal circulatory
system derived from the extra embryonic visceral endoderm.
Program/Abstract # 191
chem, a E3 ubiquitin ligase, is required for cell polarity and dorsal closure in Drosophila melanogaster.
Zamudio-Arroyo, José Manuel; Riesgo-Escovar, Juan R. (UNAM, Mexico)
chem encodes a putative E3 ubiquitin ligase. Isolated mutations in chem are embryonic lethal and have defective dorsal closure.
Embryonic dorsal closure occurs towards the end of embryogenesis and is a process whereby the lateral epithelial cells change shape,
stretching in a dorsal ward direction to close the embryo in its dorsal aspect. When this process does not occur properly, the resulting
embryos die with a dorsal cuticular hole, a mutant condition known as ‘dorsal open’. We isolated five new chem mutant alleles by
chemical mutagenesis. The analysis of mutant cuticles revealed that besides dorsal closure defects, chem mutants have other defects as
well: Early cellularization, germ band retraction, and head involution defects. chem dorsal closure phenotypes are very similar to the
mutant yurt alleles phenotypes. yurt encodes a homolog of vertebrate cytoskeletal protein band 4.1. Genetic interactions between yurt
and chem point to chem acting as a negative regulator of yurt. Immunolocalization of proteins involved in cell polarity like crumbs, β-
catenin (armadillo in Drosophila), and another protein band 4.1 homolog in flies, coracle, in homozygous chem mutant embryos,
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