Page 39 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
modulation of RA signaling may trigger olfactory repair and renewal in adults. Additional experiments have also performed to
better characterize the role of RA during neurogenesis in the early embryonic forebrain (telencephalon), the later differentiating
spinal cord, and in the generation of neuronal populations such as the dopaminergic nuclei of the substantia nigra and its target
output structure, the striatum.
The Wnt3a/b-catenin target Mesogenin1 (Msgn1) is a master regulator of presomitic mesoderm differentiation. Ravi B.
William C. Dunty Jr.
Wuhong Pei
Kristin K. Biris
Rieko Ajima
Benjamin Feldman
Terry P.
. 1)
Cancer and Developmental Biology Laboratory, Frederick National Laboratory, NIH, Frederick, MD; 2)
Division of Metabolism and Health Effects, NIAAA, NIH, Bethesda, MD; 3) Medical Genetics Branch, Vertebrate Embryology
Section, NHGRI, NIH, Bethesda, MD.
Wnts are secreted signaling molecules that function as important regulators of stem cell fates during development and disease.
A Wnt3a signaling gradient in the posterior embryo balances the self-renewal of paraxial mesoderm progenitors with their
differentiation into the presomitic mesoderm (PSM) in order to extend the embryonic body axis during gastrulation and
segmentation stages, however the underlying molecular mechanisms remain poorly understood. To understand the gene
regulatory networks regulated by Wnt3a, we performed a comparative microarray screen of wildtype and Wnt3a mutant embryos
to assess the differentially expressed genes. This approach led to the identification of the bHLH transcription factor, Mesogenin1
Msgn1), as a direct target gene of the Wnt3a/-catenin signaling pathway. Msgn1 null embryos lack posterior somites and PSM,
and display grossly enlarged tail buds filled with immature mesodermal progenitors indicative of a block in PSM differentiation
or migration. We show that Wnt3a initiates PSM differentiation via Msgn1. Overexpression of Msgn1 in mesodermal progenitors
in vivo leads to a dramatic expansion of the PSM and suppresses somitogenesis, while ectopic expression in axial mesendoderm
suppresses notochord fates. Transcriptional profiling and genomic ChIP-seq analysis show that Msgn1 overexpression in
embryonic stem cells rapidly induces PSM differentiation due to the direct activation of gene expression programs that determine
PSM identity, EMT, and the segmentation clock. Genetic epistasis analysis suggests that Msgn1 also suppresses Wnt3a in the
mesoderm, thereby establishing a feedback suppressor loop to ensure that mesodermal progenitors commit to a PSM fate. We
propose that counteracting positive and negative feedback loops initiated by Wnt3a control the balance between paraxial
mesoderm progenitor self-renewal and PSM differentiation and morphogenesis.
ENU-induced disruption of murine ESCRTII complex results in enhancement of the Fgf-Shh signaling loop with
Karen Handschuh
Matthew Koss
Elisabetta Ferretti
Michael Depew
John Manak
Kathryn Anderson
Elizabeth Lacy
Licia Selleri
. 1)
Dept of Cell and Developmental Biology, Weill Cornell Medical College, NY, NY, USA; 2)
Dept of Craniofacial Development, King’s College, London, UK; 3) Roy J. Carver Center for Genomics, University of Iowa,
Iowa City, IA, USA; 4) Program of Developmental Biology, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center,
Our laboratory uses genetic and developmental approaches, using the mouse as a model, to study morphogenesis and its
perturbations during embryonic development. We performed phenotype-based forward genetic screens by ENU mutagenesis to
uncover novel genes required for limb and craniofacial development. Mutant line 04/014 was selected based on striking limb and
craniofacial abnormalities. Mutant embryos die in utero at E16.5 with marked edema and display pre-axial polydactyly (PPD), a
common birth defect. Using high-resolution mapping and microarrays, we identified the gene responsible for the phenotype as
one of the ESCRTII complex subunits. Here, we show that receptor accumulation in ECSRTII mutants upregulates signaling. In
particular, the Ff-Shh cross-regulatory loop, which is critical for limb patterning and morphogenesis, is spatially enhanced and
temporally dilated in mutant limbs. We demonstrate that endosomal trafficking is affected in mutant cells in culture, with
engorgement of the multivesicular bodies (MVBs) and trapping of signaling molecule receptors in enlarged MBVs. Fgf4 is
spatially expanded and temporally dilated in mutant limbs, as is Shh, which, in addition, is ectopically expressed in limb bud
anterior domains. Enhancement of the Fgf-Shh cross-regulatory signaling loop underlies the PPD phenotype. Over-expression of
wild type and mutant proteins in transfection assays shows that they co-localize and co-immunoprecipitate. Genetic
complementation unequivocally demonstrates that the identified molecular lesion in ESCRTII is responsible for the observed
phenotype. These studies elucidate how endosomal trafficking of signaling receptors is critical for unique morphogenetic
processes, such as limb patterning and the establishment of digit number. They also suggest a causal link between impaired
degradation of signaling factors due to perturbed endosomal trafficking and developmental aberrations.
Diverse roles of Fibroblast Growth Factor signaling during somitogenesis and axis extension". Mark Lewandoski
Frederick National Lab for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702,
Normal extension and patterning of the vertebrate axis relies on molecular signals that coordinate various processes such as
somitogenesis, neurulation and notochord formation. Amongst the signaling families essential to this process are Bone
Morphogentic Proteins (BMPs), WNTs and Fibroblast Growth Factors (FGFs). To understand the how FGFs act in axis extension
we have begun a comprehensive study to understand FGF genetic redundancy in this process. I will review our most recent work
that defines the relationship between FGF and WNT signals to control the molecular clock that drives the periodicity of