Short interfering RNA siRNA

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Short interfering RNA

siRNA

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Part I: Gene silencing exist in many multicellular organisms

roundworm C. elegans

fungus Neurospora

fruitfly

Drosophila

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Gene silencing go back to the earliest epochs of life on Earth

 This ancient immune

system seems conserved over 1.5 billion years

...thus we can learn about different aspects of gene

and RNA silencing wherever it is easiest... plants...

roundworms... flies...

human cell lines...

Wang, Kumar & Hedges, 1999

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A brief history of RNA silencing



1998: Andrew Fire and colleagues show that double-stranded RNA induce gene silencing in C. elegans

• 1999: Hamilton & Baulcombe find

small RNA where genes are silenced in plants

• 2001: Thomas Tuschl and

colleagues show that synthetic

small RNA introduced into human cells can silence human genes

• 2000: Greg Hannon and colleagues

isolate Dicer, the siRNA producing

RNase-III enzyme in Drosophila

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13.10 RNA Interference Is Related to Gene Silencing

• RNA interference triggers degradation of mRNAs

complementary to either strand of a short dsRNA.

Figure 13.21

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Model for RNAi mechanism

Hammond et al., 2001 Dicer

(RNA-induced silencing complex) Initiation step

Effector step

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Produzione di siRNA

•Brummelkamp, 2002; Paddision, 2002; Miyahishi, 2002; Paul, 2002; Sui, 2002;

Lee, 2002; Jacque, 2002; Yu, 2002; Yang, 2002

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Inhibition of cholesterol

synthesis by siRNA: A recent study by Alnylam Inc

• "...Administration of chemically modified siRNAs resulted in silencing of the apoB messenger RNA in liver and jejunum,

decreased plasma levels of apoB protein, and

reduced total cholesterol. " Soutschek et al,

Nature, 2004

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• microRNA comes from microGenes, transcripted as ~70 nt hairpins, and processed (as is shRNA) to short ~21-mer RNAs...

More small RNA exist

• stRNA (short temporal RNA, also called micro-RNA,

miRNA) inhibit mRNA translation (Lee & Ambros,

1993; Reinhart, 2000; Lee, 2001; Lau, 2001; Lagos-

Quintana, 2001; Llave, 2002; Lim, 2003)

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13.9 MicroRNAs Are Regulators in Many Eukaryotes

• Animal and plant genomes code for many short (~22 base) RNA molecules called microRNAs.

• MicroRNAs regulate gene expression by base

pairing with complementary sequences in target

mRNAs.

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