Page 34 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
34
Models of Human Disease
1
Exploring Neural Tube Closure via Genes, Environment, and Imaging. Lee Niswander
.
Pediatrics, Univ of Colorado School
of Medicine, Aurora, CO.
Neural tube closure requires the spatial and temporal coordination of multiple tissues (neural ectoderm, the neighboring
mesenchyme and overlying ectoderm) and multiple developmental processes (proliferation, patterning, etc) to direct the
morphogenetic movements that bring the neural folds together to form the primordia of the brain and spinal cord. Defects in any
of these processes can lead to neural tube defects (NTDs). To identify novel genes involved in neural tube closure we have
undertaken ENU mutagenesis and forward genetic screens in mice. From this we have identified a large number of unexplored
genes and determined their mechanisms of action. Recent examples include roles in spatial and temporal regulation of
proliferation and the transcriptional regulation of a set of genes involved in epithelial adhesion and apical junction formation
suggesting a coordinated regulation of protein expression needed for epithelial-mediated morphogenesis. The etiology of NTDs is
complex and involves both genetic and environmental factors. The most effective environmental influence in decreasing the risk
for NTDs in humans is folic acid (FA) fortification. However, only a few mouse models have been tested for FA responsiveness
and very little is known of the mechanisms underlying FA action or the extent to which molecular pathway information can be
applied to determine which mutations may be environmentally sensitive. Although FA supplementation is clearly efficacious in
reducing human NTD incidence, contrary to expectations, we found that some mouse genetic mutants respond in a surprisingly
negative way to FA supplementation, showing an increased incidence of NTDs in homozygous mutants, occurrence of NTDs in
heterozygous embryos and embryonic lethality prior to NT closure. Our unexpected findings highlight the need to understand
how FA influences NT closure and the mechanisms and genetics underlying the response to FA supplementation. Neural tube
morphogenesis is highly dynamic, yet has largely been studied in static images. Our lab has coupled the ability to culture the
mouse embryo with confocal imaging technology and fluorescent lines to provide a dynamic view of NT closure in a living
mammalian embryo. This allows a real-time visualization of cell movements and behaviors during NT morphogenesis in the
mouse. We are now coupling live imaging with our genetic mutants to visualize how these genetic changes affect the cell
behaviors of NT closure.
2
A gene within the modifier locus,
Tgfbm3
,
regulates signal transduction
via
TGF-b type I receptor to modify vascular
phenotypes in mice and in HHT patients.
Kyoko Kawasaki
1
,
Sylvia Espejel
1
,
Tom Letteboer
1,2
,
Michael Benzinou
1
,
Marie
Lee
1
,
Ritu Roy
1
,
Hans Kristian Ploos van Amstel
2
,
Cornelius Westermann
3
,
Rosemary Akhurst
1
. 1)
HDFCCC, UCSF, San
Francisco, CA; 2) Department of Medical Genetics, University Medical Centre, Utrecht, The Netherlands; 3) St. Antonius
Ziekenhuis, Nieuwegein The Netherlands.
TGF-1, encoded by
Tgfb1
,
plays a central role in many diseases, including cancer, cardiovascular disease, autoimmunity and
fibrosis. To interrogate biological mechanisms that regulate TGF-1 biology
in vivo
,
we previously undertook genetic modifier
screens in order to genetically map and characterize variant loci that can suppress prenatal lethality of
Tgfb1-/-
mouse embryos
caused by vascular dysgenesis. We show that one of these loci,
Tgfbm3
,
is complex and can be genetically dissected into three
regions with positive
versus
negative activities in suppressing
Tgfb1-/-
prenatal lethality. Utilizing genetic or pharmacological
inhibition of candidate genes in
in vivo
and
in vitro
assays, we have identified a gene that directly interacts with the TGF type I
receptor to modulate down-stream signaling pathways and vascular phenotypes. In humans, this gene shows genetic association
with disease severity in the human TGF-vasculopathy, Hereditary Hemorrhagic Telangiectasia (HHT), which is caused by
mutations in E
NG
,
a type III receptor for TGF-/BMP. In a mouse model, these genes interact to cause disorganized retinal
vascular development
in vivo
,
reminiscent of the telangiectases and arteriovenous malformations seen in some HHT patients.
3
Phenotypic and Molecular Analyses of Different
vangl2
Mutants Demonstrates Dominant Effects of the
Looptail
Mutation
during Hair Cell Development.
Haifeng Yin, Catherine Copley,
Michael Deans
.
Dept. of Otolaryngology/HNS, Johns Hopkins
University School of Medicine, Baltimore, MD.
Experiments utilizing the
Looptail
mutant mouse, which have craniorachischisis due to a missense mutation in
vangl2
,
are
widely used as a developmental model for human neural tube defects. In this context,
vangl2
directs convergent extension
movements of the neuroectoderm via planar cell polarity signaling.
Looptail
has also been an important model for studying the
planar polarity of sensory receptor hair cells in the mouse inner ear where it directs the polarized morphogenesis of stereocilia
bundles in both the auditory and vestibular systems. As the name indicates,
Looptail
heterozygotes have distinctive looped tails
suggesting that the mutation has a semi-dominant phenotype. However it is unclear how mutant Vangl2 protein could exert a
dominant effect in these mice because the mutant protein is unstable and is not delivered to the cell surface like normal Vangl2.
We addressed this by comparing vestibular hair cell development in the inner ears of
Looptail
mice and
vangl2
knockout mice
missing a large portion of the
vangl2
gene, and by assaying molecular interactions between mutant Vangl2 and normal proteins
in
vitro
and
in vivo
.
Overall the
vangl2
knockout phenotype is milder than compound mutants with both
the
Looptail
and
vangl2
knockout alleles. In compound mutants, more hair cells are affected and individual hair cells show greater