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Fig. 6. Transition of pluripotent cells and function of Mbd3. Pluripotency
(indicated as black shading in cells and embryos) is passed on from the 3.5
dpc ICM to the early epiblast of 4.5 dpc embryos, and then to the late
epiblast of 5.5 dpc embryos. During this transition, the expression levels of
the listed genes change as shown. Loss of Mbd3 results in misregulation of
genes with asterisks at 3.5 dpc and/or 4.5 dpc, followed by failure of
epiblast proliferation and proaminiotic cavity formation at 5.5 dpc. Whereas
Nanog downregulation occurs between 3.5 and 4.5 dpc, it is not clear
whether expression levels increase during ES cell derivation, or whether ES
cells are derived from rare Nanog high-expressing cells at 4.5 dpc.
Mbd3/NuRD is required for proliferation of ICM cells in vivo and for isolated
ICMs to give rise to a proliferating epiblast in the presence of LIF in
culture. Mbd3 is also required for lineage commitment in ES cells
(Kaji et al., 2006 ).
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7 integrin
(red). (B) Whole-mount in situ hybridisation of heterozygous (top) and
homozygous null (bottom) embryos at 5.5 dpc for Cdx2 (left-hand
panels), and Mash2 (right-hand panels). (C) Heterozygous (top
panels) and homozygous null (bottom panels) embryos at 5.5 dpc were stained
for Gata4 (red) and Oct4 (green). A close-up of the homozygous null embryo is
shown in the inset at the bottom of each panel to illustrate co-expression of
Oct4 and Gata4 in a subset of cells (arrow), in addition to Oct4 or Gata4
single-positive cells (asterisk and arrowhead, respectively). (D)
Chimeric embryos made with wild-type ES cells expressing GFP (green) and
embryos obtained from Mbd3 heterozygote intercrosses. The genotype of the
embryo used for each chimera was determined by Mbd3 staining (red) in
GFP-negative (i.e. host-derived) cells.
