(epigenetics)

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? ? ? ? ?
(epigenetics)
??? ????????????
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(No Transcript)
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??????
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???? ?? (gene expression pattern)
?????????????,????????,???????????????????????????
??????????????????????????
???????????????????      ??????DNA??????
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???????????
DNA????????????       (????????)
?????? (epigenetic modification)
???????(chromatin remodeling)         
(?????????)
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????(epigenetic inheritance)???????????????DNA??
??????
?????(epigenetics)???????DNA????????????????????
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????????
DNA?????????
?????
???? ????
????????
X?????
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(?) DNA?????????
DNA???(DNA methylation)?????????????????????
?,??????DNA??????5?????????????,?????????5?????(5-
methylcytosine,5-mC)?
DNA???
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DNA???
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DNA ???
DNA?? ???
DNA??????????
DNA???
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???????DNA?5-mC????????2--7,????5-mC???CpG????(C
pG doublets)?
????5?????CpG?????????CpG?(CpG islands)?
DNA???
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??????(????)??CpG???5-mC???????????DNA???,??DNA???
???????(gene silence)????????(non
-methylated)????????(gene activation)?????????(dem
ethylation)??????????????(reactivation)????
DNA???
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Model for methylation-dependent gene silencing.
The structural element of chromatin is the
nucleosomal core, which consists of a 146-bp DNA
sequence wrapped around core histones.
Acetylation of the histones causes an open
chromatin config-uration that is associated with
transcriptional activity. Methylated cytosines
are recognized by methyl-CpG-binding proteins
(MBDs), which in turn recruit histone
deacetylases (HDACs) to the site of methylation,
convert-ing the chromatin into a closed structure
that can no longer be accessed by the
transcriptional machinery.
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??????????????????????,?????????????,?????????????
?????????,????????????????????????????????????????
(euchromatin)?????????????????????????????(hetero
-chromatin)????????????
?????
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Epigenetics is an advanced biological system
that selectively utilizes genomic information and
is involved in various fundamental phenomena.
Specifically, it puts emphasis on the regulation
of gene expression, through DNA methylation,
chromatin, and post-translational modification of
proteins such as histones. Arrows indicate
possible functional interactions between them.
DNA hypermethylation, histone hypoacetylation and
inactive chromatin repress transcription. In
contrast, a transcriptionally active condition
may encourage DNA hypomethylation, histone
hyperacetylation and active chromatin. Also, a
particular chromatin structure may be required
for establishing DNA methylation .
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????     ??,???H3 Lys9???????????????,??H3
Lys4???????????????