Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. A. Fire et al. (1998) Nature Vol 391:

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1 Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans A. Fire et al. (1998) Nature Vol 391:

2 Outline 1. Introduction 2. Objective 3. Results 4. Mechanism 5. Summary 6. Take-Home-Lesson 7. Discussion and current questions 2

1.1 Introduction History of gene silencing - 1989, Richard Jorgensen tried to manipulate petunia plants - Goal: to intensify purple color by introduction of an

3 1.1 Introduction History of gene silencing , Richard Jorgensen tried to manipulate petunia plants - Goal: to intensify purple color by introduction of an additional pigment gene - Result: plants with paler or white flowers ; 17:51 MEZ 3

4 1.1 Introduction - History of gene silencing - In other experiments it was tried to make plants resistant to viral infection - over expressed protein should block replication of the virus - replication was restricted - but: the protein was not necessary - just the RNA 4

5 1.1 Introduction - History of gene silencing - antisense RNA was used to knockdown gene-expression - sense RNA had a same effect - RNA-gene-relation in sequence was necessary 5

6 1.2 Introduction - C. elegans - nematode - model organism - rapid generation time - hermaphrodite and sexual reproduction - simple body plan - exact known number of somatic cells 6

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8 ; 17:50 MEZ 8

9 ssrna und asrna equal effect can persist in next generation, even though native RNA transcripts are degraded in progeny cells 2. Objective Investigation of requirements for structure and delivery of the interfering RNA. 9

10 3.1 Results - surmised double stranded-character - injected RNA was synthesized by bacteriophage RNA polymerase: random transcripts - aberrant RNA products were found in DNA transgene assays 10

11 3.2 Results - Comparing interference activities - unc-22 gene: encodes myofilament protein in striated muscle cells - decrease of unc-22 gene expression: twitching phenotype thousand copies of unc-22 mrna are present in these muscel cells - null mutant: strong twitching 11

12 3.2 Results - Comparing interference activities - antisense and sense RNA: small-scale interference - sense-antisense mixture: effective interference - electrophoretic analysis: the injected mixture was double-stranded 12

13 3.3 Results - conditions of annealing - Annealing of ds RNA before injection was not necessary - Mixing the as and s RNA in low-salt conditions: interference - rapid sequential injection of as and s RNA: interference - sequential injection (interval > 1h): marginal interference - conclusion: ss RNA may be degraded 13

14 3.4 Results - Specificity - Co-injection of unc-22 unrelated ds RNA: no increased interference - Injection of construct with ds segment in cis to ss segment: no increased interference - Conclusion: Interference is not potentiated by unspecific panic-response mechanism 14

15 3.5 Results - unc-54, fem-1 and hlh-1 - unc-54: body-wall-muscle heavy-chain isoform of myosin, required for full muscle contraction - fem-1: ankyrin-repeat-containing protein, required in hermaphrodites for sperm production - hlh-1: myod-family protein, required for proper body shape and motility 15

16 3.5 Results - unc-54, fem-1 and hlh-1 - injection of related ds RNA: progeny broods showed null-mutant phenotype - injection of related as or s RNA: progeny broods showed no significant interference 16

17 3.5 Results - unc-54, fem-1 and hlh-1 - Exception: unc-54c showed a larval arrest phenotype (not similar to null-mutant) - explanation: unc-54c segment encodes a highly conserved myosin-motor domain - interference may be knocked down genes with same or homologous motor domain 17

18 3.6 Results - fluorescent reporter proteins 18

19 3.6 Results - fluorescent reporter proteins - embryonically derived muscle cells: no resistance to interference - postembryonically derived striated muscle cells: more resitance to interference - non-striated vulval muscels (late larval growth): resitance to interference 19

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21 3.7 Results - Effects of RNA interference on mrna levels - mex-3 is abundant in early embryos and gonads - ds mex-3 RNA for elimination of endogenous mex-3 mrna - verification by in situ hybridization 21

22 3.8 Results - dsrna is able to cross cellular boundaries 22

23 4. Mechanism 23

24 4. Mechanism 24

25 5. Summary as and srna cause equal marginal downregulation by interference dsrna is able to knock down genes by effective interference dsrna must be related to an endogenous Exon-sequence (related genes may be silenced too) Interfering Effects persist in progeny brood interfering effects are not related to panic-response-mechanism dsrna mediated interference is able to cross cellular boundaries a few cells will escape from these interfering effects Fire and Mello received the Nobelprize in 2006 "for their discovery of RNA interference - gene silencing by double-stranded RNA" 25

26 6. Take-Home-Lesson - RNAi by double-stranded RNA is a potent and specific tool to regulate gene expression in eucaryotes 26

27 7. Discussion and current questions - What is RNAi? - What is the mechanism of mrna down regulation by double-stranded RNA? 27

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