Biology Reference
In-Depth Information
Activation
Post-MBT
activation
MBT
priming
Pre-MBT
Pre-patterning
H3K36me3
RNAPll
H3K4me3
H3K27me3
H3K9me3
Repression
MBT/Post-MBT
or
or
Figure 3.5 Model of prepatterning and priming of embryonic gene expression before
and after the MBT. A “prepatterning” of expression profiles is set by histone modifica-
tions on a subset of housekeeping and developmentally regulated genes during pre-
MBT development, before ZGA. These modifications may occur alone (e.g., H3K4me3
only) or in combinations (e.g., H3K4me3 together with H3K27me3 or H3K9me3). At
the MBT, on genes that are to be activated (right, upper panel), “priming” for activation
takes place with enhanced H3K4me3, RNAPII loading at the TSS and moderate H3K36
occupancy in the 5
0
end of the gene. Full activation post-MBT, that is, after ZGA onset, is
accompanied by spreading of RNAPII and H3K36me3 along the coding region. On genes
that are to be repressed, or kept in a repressed state at and after the MBT (right, lower
panel), various chromatin states are detected, with enrichment in H3K27me3, H3K9me3,
or both marks. Note that some genes may also lose the pre-MBT marks altogether.
speculatively (at present) in the form of DNA methylation, transposons,
noncoding RNAs, or even sequence determinants (
Lindeman et al.,
2011
). Several lines of evidence support this possibility (
Aravin &
Bourc'his, 2008; Bogdanovic et al., 2011; Branciamore, Chen, Riggs, &
Rodin, 2010; Illingworth et al., 2010; Lienert et al., 2011; Thomson
et al., 2010; Weber et al., 2007; Wu, Zhang, & Cairns, 2011
), although a
formal demonstration remains pending.
REFERENCES
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, 1328-1338.
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Current Opinion in Genetics and Development
,
19
, 396-403.
Aday, A. W., Zhu, L. J., Lakshmanan, A., Wang, J., & Lawson, N. D. (2011). Identification
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