Rnai mediated pathways in the nucleus
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RNAi-MEDIATED PATHWAYS IN THE NUCLEUS. Marjori A.Matzke* and James A.Birchler. RNAi. 分布: plant, animal and fungi. 長度 : 21~26 nt 來源 : dsRNA 經由 Dicer (RNaseIII enzyme) 作用後製造出 small interfering RNA(siRNA) 作用原理 :

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RNAi-MEDIATED PATHWAYS IN THE NUCLEUS

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Rnai mediated pathways in the nucleus

RNAi-MEDIATED PATHWAYS INTHE NUCLEUS

Marjori A.Matzke* and James A.Birchler


Rnai mediated pathways in the nucleus

RNAi

分布:plant, animal and fungi

長度:

21~26 nt

來源:

dsRNA 經由 Dicer (RNaseIII enzyme) 作用後製造出small interfering RNA(siRNA)

作用原理:

利用siRNA辨認特定mRNA序列並且利用 RNA-induced silencing complex (RISC)執行 target-mRNA cleavage 造成 mRNA degradation , 而依照target sequence 和effect complex的組成而有不同的silencing形式出現


Rnai mediated pathways in the nucleus

特別的形式:

利用RNA-dependent RNA polymerase (RdRP)

來藉由ssRNA製造dsRNA來起始或放大RNAi的作用

Example:

Transposons 和 viruses在replication時製造dsRNA


Rnai mediated pathways in the nucleus

MicroRNA (miRNA):

可藉由 targeting mRNA 誘導出silencing

來源:

miRNAs are produced through processing by Dicer of

imperfect RNA hairpins, which are typically encoded in

non-protein-coding regions of plant and animal

genomes.


Rnai mediated pathways in the nucleus

Dicer

Proteins of the Dicer family are ribonuclease III enzymes that process dsRNA to produce small RNAs.

RNA-dependent RNA polymerases

These synthesize dsRNA from an ssRNA template to initate or amplify the RNAi process.

Argonaute

Members of this family provide the small RNA-binding component of silencing-effector complexes.


Overview of nuclear pathways

Overview of nuclear pathways

  • RNA-directed DNA methylation (RdDM)

  • RNAi-mediated heterochromatin formation

  • DNA elimination

  • the silencing of unpaired DNA during meiosis


Rnai mediated pathways in the nucleus

RNA-directed DNA methylation (RdDM)

利用DNA-dependent RNA polymerase

使RNA帶有訊號

利用RNA-dependent RNA polymerase2

大概是使DNA可容易接近RNA signal

MET1:只針對CGs的cytosine甲基化

DRM2:只針對非CG的cytosine甲基化

在RNA消失後甲基化的維持

去甲基化,使gene再活化

可能和small RNA有關


Properties of heterochromatin

Properties of heterochromatin.

  • heterochromatin is gene-poor relative to euchromatin and it surrounds the centromeric region in many species.

  • Heterochromatin is usually not conducive to high levels of gene expression


Rnai mediated pathways in the nucleus

RNAi-mediated heterochromatin formation

Heterochromatin中的Tandem repeat or multiple copies of transposable elements

藉由RdRP轉換成雙股形式

siRNA被認為引導histone methyltransfrease到chromatin進行H3k9的甲基化


Rnai mediated pathways in the nucleus

DNA elimination

that internal eliminated segment (IES) elimination and other genome alterations occur. Cells then separate and one micronucleus degenerates

Early in conjugation, the micronuclear genome is bidirectionally transcribed

The resulting dsRNA is processed by Dicer into small RNAs, termed scan RNAs (scnRNAs)

The scnRNAs are exported into the old macronucleus, and those that can base pair to genomic DNA (red dotted lines) are degraded. The remaining scnRNAs, which correspond to sequences eliminated in the previous conjugation, migrate to the developing new macronucleus


Rnai mediated pathways in the nucleus

the silencing of unpaired DNA during meiosis

內圈RNA以DNA-dependent RNA polymerase合成

已內圈當模板合成出收股RNA

可能被製造出siRNA,尚未被研究出來

Small RNA+RISC+AGO

辨認Homologous unpaired region


Conclusions

Conclusions

Furthermore, the phylogenetic distribution of the four known RNAi-mediated nuclear pathways is not yet known.

Does RdDM occur regularly in mammals?

Are there examples of programmed DNA elimination mediated by RNAi in organisms other than ciliates?

還有許多疑問尚未被解答出來,期待科學家努力的成果,也期待有更進步的科學幫助我們探訪這個奇妙的世界!


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