Biology Reference
In-Depth Information
Before cold
Cold exposure
Back to warm
conditions
A
1-2 weeks
3-4 weeks
FLC
COOLAIR
COLDAIR
VIN3
B
C
D
Figure 6.1 Chromatin-based repression of FLC during vernalization. The following
features are depicted at different stages before, during and after prolonged exposure
to cold. (A) Expression levels of FLC mRNA, COOLAIR noncoding antisense RNAs, COL-
DAIR noncoding sense RNA, and VIN3 mRNA. (B) Location of the different transcripts
over the FLC locus. The transcription start site of the three types of transcripts is indi-
cated by colored arrows. (C) H3K27me3 enrichment over the FLC locus. (D) Bistable
expression of FLC in individual cells within a tissue. Black dots represent nuclei of cells
expressing FLC. Before cold exposure, FLC sense mRNA levels are high in all cells. Soon
after cold exposure, FLC expression is downregulated in some cells concomitantly with
the transcription of COOLAIR. Longer exposure to cold triggers the expression of COL-
DAIR that recruits a catalytically active PRC2 complex at the nucleation region around
the TSS of
, which results in the local enrichment of H3K27me3. This leads to an
increasing number of cells in which
FLC
switches to a repressed state. Return to warm
temperature after at least 4 weeks of cold exposure results in stable
FLC
silencing asso-
ciated with the spreading of VIN3-PRC2 and H3K27me3 over the whole locus.
FLC
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