Page 44 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
DNA Oxidation towards Totipotency in Mammalian Development. Guo-Liang Xu
Institute of Biochemistry and Cell
Biology, Chinese Academy of Sciences, Shanghai, China.
Sperm and eggs carry distinctive epigenetic modifications that are adjusted by reprogramming following fertilization. The
paternal genome undergoes active DNA demethylation before the first mitotic division. The biological significance and
mechanisms of paternal epigenome remodeling are unclear. We find that, within mouse zygotes, oxidation of occurs in the
paternal genome, changing 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). In Tet3 oxidase-deficient zygotes
derived from conditional knockout mice, the conversion of 5mC into 5hmC fails to occur. Thus, the loss of 5mC in the paternal
genome in zygotes is caused by its conversion to 5hmC mediated by Tet3. Deficiency of Tet3 also impedes demethylation at the
paternal copy of genes such as Oct4 and Nanog and delays the subsequent reactivation of Oct4 in early embryos. Heterozygous
mutant embryos lacking maternal Tet3 suffer increased developmental failures. Importantly, oocytes lacking Tet3 also show
impaired reprogramming of injected somatic cell nuclei. We conclude that Tet-mediated oxidative DNA demethylation is
essential for epigenetic reprogramming in the early embryo following natural fertilization, as well as for the reprogramming of
somatic cell nuclei during animal cloning.
DNA dioxygenases regulate cardiac progenitor pool and their differentiation in heart development. Qing-Yan Cui
Liang Xu
Bin Zhou
. 1)
Group of DNA Metabolism, The State Key Laboratory of Molecular Biology, Institute of Biochemistry
and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China; 2) Key
laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese
Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Shanghai 200031, China.
The Tet family functions as dioxygenases to oxidize 5-methylcytosine (5mC), which is thought to play an important role in
DNA demethylation and gene activation. However, little is known about the biological significance of this modification in
development. To reveal the role of Tet family in vivo, we generated Tet1 and Tet3 mutant mice. Single ablation of Tet1 or Tet3
does not lead to any embryonic developmental defect. However, depletion of both genes leads to embryonic death at mid-
gestation due to severe heart defects, including thin compact myocardium and hypoplastic trabeculae at E11.5. Consistent with
this phenotype, we found that cardiomyocyte proliferation was significantly decreased in double mutant hearts. Surprisingly,
embryos lacking both Tet1 and Tet3 displayed an expansion of the Isl1-positive progenitor cell population at E9.5. Consistently,
the Tet1/Tet3 depleted ES cells displayed defective differentiation ability towards cardiomyocytes in embryonic body (EB)
differentiation assays, with reduced percentage of spontaneously beating foci within an individual EB, and down-regulated
mature cardiomyocyte markers such as MHC, MHC and MLC2a, but up-regulation of cardiac progenitor marker Isl1.
Collectively, our data shows an unexpected redundant function of Tet1 and Tet3 in vivo and in vitro, indicating the significance
of oxidation-dependent demethylation during early mouse heart development.
Dissection of the molecular mechanism that regulates activation of murine IAP (intracisternal A particles)
retrotransposons upon DNA demethylation in ES cells.
Jafar Sharif
Takaho A. Endo
Kayoko Katsuyama
Yoko Kuroki
Tomoyuki Ishikura
Takanori Hasegawa
Osamu Ohara
Tetsuro Toyoda
Yoichi Shinkai
Haruhiko Koseki
. 1)
RIKEN Center for Allergy & Immunology (RCAI), Japan; 2) RIKEN Bioinformatics and Systems
Engineering Division (BASE), Japan; 3) RIKEN Advanced Science Institute (ASI), Japan.
IAPs (intracisternal A particles) are a class of endogenous retroviruses (ERVs) that are presently highly active in the rodent
genome. In murine embryonic stem (ES) cells, IAPs are rigorously silenced by repressive epigenetic modifications such as DNA
and H3K9 methylation. The SRA protein Np95 is the only protein known today that can recognize both DNA and H3K9
methylation marks in mammals, suggesting the possibility that Np95 could be a key mediator for IAP regulation. In this study, by
using various conditional knockout ES cells for Np95, Dnmt1 (maintenance DNA methyltransferase) and Eset/Setdb1 (H3K9
trimethylase), we report that Np95 might have a role for DNA demethylation induced IAP activation and that this could be
mediated by at least two pathways, namely, reduction of H3K9 trimethylation, and, recruitment of positive transcription factors
such PTEF-b at the IAP loci. Moreover, our results implicate that this function of Np95 could be dependent on the recognition of
hemi-methylated DNA generated by passive DNA demethylation. Collectively, these results provide the first mechanism to
elucidate how retrotransposons could be activated upon loss of DNA methylation and show that Np95 could regulate the dynamic
interplay between DNA and H3K9 methylation by recognizing both these modifications to control IAP transcription.
Alterations in genomically imprinted noncoding RNA clusters in a mouse model of Fetal Alcohol Spectrum Disorders
FASD). Benjamin Laufer
Janus Katherine, Kleiber Morgan, Eric Diehl, Sean Addison, Shiva Singh. Biology, Western