发育生物学——microRNA.ppt
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1、microRNA的调控,RNA干扰造成的基因沉默,Gene knock-outs:remove the function of a gene permanently by disrupting its DNA;Gene silencing:suppress gene function by destroying or inhibiting mRNA(introducing RNA either binds to the mRNA and prevents it from being translated,or targets a nuclease to bind to the mRNA and
2、 degrade it)RNA interference(RNAi)recruits a natural RNA-degrading mechanism that is apparently ubiquitous in multicellular eukaryotes from plants to mammals.The phenomenon was first uncovered in plants during transgenic experiment:mRNA rapidly degraded.,2006年的诺贝尔生理学奖获得者:,Andrew Z.FireCraig C.Mello,
3、双链RNA抑制含其同源序列基因的表达,Effects of mex-3 RNA interference on levels of the endogenous mRNA(in situ hybridization in embryos)(胚胎的原位杂交).,No hybridization and staining,+hybridization(endogenous mex-3 RNA),+antisense+hybridization,+ds mex-3 RNA+hybridization,Why exogenous dsRNA can inhibit expression of gene
4、s homologous to that RNA?,从双链RNA产生的小干扰(small interfering)RNA(siRNAs)可以指导用不同机制关闭基因的细胞机器,RNAi silencing,Exogenous dsRNA外源双链RNA,RNA 干扰造成的基因沉默,Dicer:double-stranded RNAs to short interfering RNA(siRNA)siRNA incorporated into a nuclease-containing protein complex known as RISC(RNA-induced silencing compl
5、ex,including a ribonuclease called Argonaute);siRNA acts a“guide RNA”to target RISC to any mRNA containing an exactly complementary sequence.The mRNA is then degraded by the nuclease in the RISC.,The targets of the RNAi-directed gene silencingDegradation of the target mRNA(引起靶标mRNA的降解),Inhibition of
6、 translation of the target mRNA(抑制靶标mRNA的翻译),Silencing the gene transcription from the target promoter(引起靶标启动子的转录沉默).,miRNA processing:Drosha,Dicer,Core of the RNAi mechanismDicer:an RNaseIII-like multidomain ribonuclease that first processes input dsRNA into small fragments called short interfering
7、 RNAs(siRNAs)or microRNAs(miRNA).Dicer then helps load its small RNA products into RISC.RISC(RNA induced silencing complexes)(RNA诱导的沉默复合体):a large multiprotein complex that direct the bound siRNA or miRNA to its target and inhibit the target gene expression.,Dicer:,Structural organization:-A PAZ dom
8、ain,binds the end of the dsRNA-Two RNase III domains-Other non-conserved domains.,RISC:the key component is Argonaute(AGO),AGO2,Dicer,TRBP,The multiple functions of RNAi,MicroRNA(miRNA),A type of non-coding small RNA(2123 nucleotides)Produced by Dicer from a stem-loop structured RNA precursor(70-90
9、nt)(结构和来源).miRNAs are widely expressed in animal and plant cells as RNAprotein complexes,termed miRISCs,and have been implicated in the control of development because they lead to the destruction or translational suppression of target mRNAs with homology to the miRNA(生物学功能和机制).,microRNA 介导的基因沉默,miRN
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