Page 46 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
depleted, these genes are downregulated with decreased H2BK120ub1. Collectively, our results suggest that Rnf20 is a potential
master epigenetic control of DNA replication and gene transcription in ES cells, maintaining the stable undifferentiated state.
Upregulation of the mammalian X chromosome is associated with enhanced transcription initiation and epigenetic
modifications. Xinxian Deng
Joel Berletch
Joseph Hiatt
Di Kim Nguyen
Jay Shendure
Christine Disteche
. 1)
Pathology, Univ Washington, Seattle, WA; 2) Dept Genome Sciences, Univ Washington, Seattle, WA; 3) Dept Medicine, Univ
Washington, Seattle, WA.
X upregulation in mammals increases expression of X-linked genes to compensate for bi-allelic expression of autosomal genes.
Here we present the first evidence of a molecular mechanism that enhances X transcription based on differential enrichment in
specific marks on the active X chromosome. Histone H4 acetylated at lysine16 and the corresponding acetyltransferase MOF
known to mediate upregulation of the Drosophila X chromosome, were specifically enriched at the 5 end of active mouse X-
linked genes. In addition, H2AZ and the transcriptional initiation form of RNA polymerase II (PolII-S5p) were also specifically
enriched at the 5' end of X-linked genes. Importantly, depletion of MOF or of MSL1, two conserved components of the
Drosophila upregulation complex, caused a decrease in PolII-S5p and in expression of mouse X-linked genes. Our results suggest
that the MSL complex plays a role in mammalian X upregulation via enhanced transcription initiation.
Nuclear transfer for the study of X chromosome inactivation in mice. Atsuo Ogura
Shogo Matoba
Mami Oikawa
Kimiko Inoue
Fumitoshi Ishino
. 1)
BioResource Center, RIKEN, Tsukuba, Ibaraki, Japan; 2) Graduate School of Life and
Environmental Science, University of Tsukuba, Ibaraki, Japan; 3) Department of Epigenetics, Medical Research Institute, Tokyo
Medical and Dental University, Tokyo, Japan.
Cloning by nuclear transfer into enucleated oocytes is the sole reproductive engineering technology that endows the donor cells
genome with totipotency. Besides its practical applications in production of cloned animals, the nuclear transfer technique can
provide invaluable experimental models for the study of mammalian epigenetics. Comparisons of the epigenetic patterns of
mouse embryos cloned from donor cells at different times of the life cycle can determine the nature of the epigenetic changes
during development and their underlying mechanisms. These include DNA methylation, histone methylation, genomic
imprinting, and X chromosome inactivation (XCI). XCI normally triggers inactivation of one of the two X chromosomes in
female embryos so that the gene dosage can be compensated with that in males. XCI is established by
RNA coating in
somatically cloned embryos of both sexes,
was ectopically expressed from the active X chromosome and this perturbation
critically affected development of cloned embryos, as revealed by knockout and knockdown experiments. We then extended our
XCI analysis to nuclear transfer using different types of germ cells of both sexes. The results suggested that
is expressed at
zygotic gene activation in the default mode and only the genome which has passed through oogenesis can repress this expression.
This is the most probable reason why somatically cloned mouse embryos ectopically express
from the active X chromosome.
This finding strongly supports the idea of the existence of a maternal imprint resistance to XCI. Furthermore, we also found that
shortly after implantation the aberrant XCI status in cloned embryos had been corrected autonomously in both embryonic and
extraembryonic tissues, indicating the presence of a newly established XCI control for postimplantation embryos of the both
Keynote Address
Development of Hematopoietic Stem Cell: A final scenario. Shinichi Nishikawa
Riken Center for Developmental Biology,
Kobe, Kobe, Japan.
A large gap has existed in our understanding of the course of differentiation from mesoderm to definitive haematopoietic stem
cells (HSCs). Recently, Flk1+ mesoderm that expresses Etv2 was determined to be the source from which the progenitors of all
endothelial (EC) and blood cells are segregated from other lineages. This result justifies to use Flk1+Etv2+ mesoderm (Etv2-
induced mesoderm, ETM) as the starting point of prospective analysis of differentiation course of HSC and EC. With this
rationale in mind, we analyzed the progression of HSC differentiation from this Etv2-induced mesoderm (ETM). ETM diversifies
into Runx1-Gata1-, Runx1+Gata1- and Runx1+Gata1+ populations in the extra-embryonic region at E7.5. The fate of GATA1+
cells are almost exclusively primitive erythrocytes. Hemogenic EC and HSCs are derived from the Runx1+Gata1- population,
which moves from the extra-embryonic space to the embryo proper during E7.5 to E8.0 and contributes to the vasculature. This
migration occurs before the heartbeat is initiated and is independent of circulation. This proposed differentiation course with
circulation-independent hemogenic angioblasts would unite extra- and intra-embryonic origins of blood cells and settle the long-
running dispute about the orgin of blood cells. In this symposium, we would like to propose a new terminology of intermediate
stages toward HSC.