1. Short interfering RNA siRNA
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2. Part I: Gene silencing exist in many multicellular organisms
fruitfly Drosophila
roundworm C. elegans
fungus Neurospora
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3. Gene silencing go back to the earliest epochs of life on Earth
Wang, Kumar & Hedges, 1999
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...
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4. 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
2000: Greg Hannon and colleagues isolate Dicer, the siRNA producing RNase-III enzyme in Drosophila
2001: Thomas Tuschl and colleagues show that synthetic small RNA introduced into human cells can silence human genes
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5. 13.10 RNA Interference Is Related to Gene Silencing
RNA interference triggers degradation of mRNAs complementary to either strand of a short dsRNA.
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Figure 13.21

6. Model for RNAi mechanism
Dicer
(RNA-induced silencing complex)
Initiation step
Effector step
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Hammond et al., 2001

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9. 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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10. 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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11. 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)
microRNA comes from microGenes, transcripted as ~70 nt hairpins, and processed (as is shRNA) to short ~21-mer RNAs...
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12. 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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