Page 37 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
CHD5: Chromosome engineering, chromatin dynamics, and cancer. Alea A. Mills
Cold Spring Harbor Laboratory, Cold
Spring Harbor, NY.
Although 1p36 loss has been documented for decades and a variety of malignancies have this lesion, the tumor suppressor
mapping to this genomic interval had not been identified. Using chromosome engineering to create models with gain and loss of
the region of the mouse genome corresponding to human 1p36, we pinpointed a potent tumor suppressive interval, identified
Chromodomain Helicase DNA-binding domain protein 5 (CHD5) as the causative gene in the region, elucidated molecular
pathways induced by CHD5, and demonstrated that CHD5 is frequently deleted in human cancer. The discovery of CHD5 as a
tumor suppressor has had a major impact in the cancer field. Indeed, it is now appreciated that CHD5 is mutated in cancers of the
breast, ovary, colon, and prostate, as well as in melanoma, glioma, and neuroblastoma. Furthermore, CHD5 status is a prognostic
indicator of patient survival following anti-cancer therapy. Still, the mechanism by which CHD5 exerts its tumor suppressive role
is not well understood. CHD5 belongs to the CHD family of SWI-SNF-like ATP dependent-chromatin remodeling proteins;
however, the role of CHD5 in modulating chromatin dynamics has not been reported. Here, we show that CHD5s tumor
suppressive function is dependent on its tandem plant homeodomains (PHDs)modules that in several other chromatin-remodeling
proteins regulate transcription by binding to specific covalent modifications on histone tails. The PHDs of CHD5 preferentially
bind unmethylated H3K4 (H3K4me0), an interaction abrogated by methylation of H3K4 but unaffected by modification of
H3K9. Both loss- and gain-of-function studies reveal that CHD5 modulates transcription, and furthermore, that CHD5 is a potent
inhibitor of cellular proliferation. Mutation of residues within the PHDs of CHD5 that abolish H3 binding effectively abrogate
CHD5s ability to modulate expression of target genes as well as its ability to inhibit proliferation, leading to tumorigenesis in
vivo. These findings identify CHD5 as a member of a newly appreciated class of H3K4me0-binding PHD containing proteins
and reveal a critical role for this interaction in facilitating CHD5s cellular function, providing new insight into the molecular
mechanism responsible for the tumor suppressive role of CHD5.
Mechanisms of position-dependent specification of cell fates in preimplantation embryos. Hiroshi Sasaki
Kumamoto University, Kumamoto, Japan.
In preimplantation mouse embryos, specification of cell fates into the trophectoderm (TE) or inner cell mass (ICM) depends on
the positions of the cell within the embryos. The transcription factor Tead4 is required for specification of the TE fate. Tead4 is
present in the nuclei of all blastomeres. Cell-position-dependent Hippo signaling controls nuclear localization of the coactivator
protein Yap as well as the activity of Tead4: inactive Hippo signaling in the outer cells increases nuclear Yap levels, activates
Tead4, and promotes TE development; on the other hand, active Hippo signaling in the inner cells suppresses nuclear Yap levels,
inactivates Tead4, and promotes ICM development. In this study, we show that cell polarity and cell-cell adhesion together
establish position-dependent Hippo signaling at approximately the 32-cell stage. Cell-cell adhesion activates Hippo signaling, but
polarity in the outer cells suppresses it. The junction-associated protein Angiomotin (Amot) is essential for activation of the
Hippo pathway. In the inner cells, Amot localizes to the adherens junctions and activates the Hippo pathway, whereas in the outer
cells, cell polarity sequesters Amot from basolateral membranes to apical domains, thus suppressing the Hippo signal. We
propose that cell polarity uncouples cell-cell adhesion and the Hippo pathway by sequestering Amot from the adherens junctions.
This mechanism converts positional information into determination of the cell-fate through differential Hippo signaling.
FGF4 is required for lineage restriction and salt-and-pepper distribution of primitive endoderm program but not its
initiation in the mouse. Minjung Kang
Ania Piliszek
Jérôme Artus
Anna-Katerina Hadjantonakis
. 1)
Biology, Sloan-Kettering Institute, New York, NY; 2) Biochemistry, Cell and Molecular Biology Program, Weill Graduate
School of Medical Sciences of Cornell University, New York, NY 10065, USA; 3) Department of Experimental Embryology,
Institute of Genetics and Animal Breeding, Polish Academy of Sciences, Jastrzebiec, 05-552 Wólka Kosowska, Poland; 4)
Institut Pasteur, CNRS URA2578, Mouse Functional Genetics Unit, Paris, France.
The emergence of pluripotent epiblast (EPI) and primitive endoderm (PrE) lineages within the inner cell mass (ICM) of the
mammalian blastocyst involves initial co-expression of lineage-associated markers followed by their mutual-exclusion and the
salt-and-pepper distribution of lineage-biased cells. Thereafter lineage segregation is completed by the sorting of cells into
adjacent tissue layers. Precisely how EPI and PrE cell fate commitment occurs is not entirely clear; however in the mouse
FGF/ERK signaling is required. To gain insight into the role of FGF signaling, we investigated the phenotype resulting from
zygotic and maternal/zygotic inactivation of Fgf4. Fgf4 heterozygous blastocysts exhibited increased numbers of NANOG-
positive EPI cells and reduced numbers of GATA6-positive PrE cells, suggesting that FGF signaling must be tightly regulated to
ensure appropriate numbers of cells for each lineage. Fgf4 mutants lacked PrE entirely with their ICM comprising exclusively of
NANOG-expressing cells. Notably, an initial period of widespread EPI and PrE marker co-expression was established, even in