revisions to the “central dogma” of molecular biology

1. mRNA1 no introns protein isoform1 genomic DNA pre-mRNA with introns mRNA2 no introns protein isoform2 non-coding RNA genes over the last 10 years, scientists have discovered an entirely new category of non-coding RNA genes whose existence had never even been suspected; they are distinguished by their small sizes relative to traditional RNA genes (i.e. 21 to 25 bp versus 96 bp) and are therefore commonly referred to as “microRNAs” revisions to the “central dogma” of molecular biology

2. The Nobel Prize in Physiology or Medicine 2006 Andrew Z. Fire Stanford University School of Medicine b. 1959 Craig C. Mello University of Massachusetts Medical School b. 1960 for their discovery of RNA interference gene silencing by double-stranded RNA

3. microRNA-mediated gene silencing is observed in plants, animals, and many fungi; it plays essential roles in development and virus resistance; it has already provided powerful tools for studying gene function and spawned new therapeutic industries Saumet A, Lecellier CH. 2006. Retrovirology 3: 3 microRNA biogenesis and actiongene silencing is mediated by short double-stranded RNAs (dsRNAs)

4. biologists working with transgenic plants had long observed a bewildering array of unanticipated gene silencing phenomena; in 1998, Fire and Mello compared the silencing activity of single-stranded RNAs (ssRNAs) (sense or antisense) with double-stranded (dsRNAs) hybrids; marginal silencing was achieved by injecting C. elegans with ssRNAs, but potent and specific silencing was achieved by injecting a sense-antisense mixture; in other words it is the dsRNAs that matter

5. ingestion of bacteria expressing dsRNAs is as effective for gene silencing as the direct injection of dsRNAs C. elegans scientists can silence nearly any desired gene just by feeding the worm with one of these custom-modified bacteria they sell on the Internet Fraser AG, …, Ahringer J. 2000. Nature 408: 325-330 (notice how few genes have an identifiable phenotype) functional genomics of C. elegans chromosome 1 by RNA interference

6. percentages for all genes (blue bars) or all genes with RNAi phenotype (red bars) that have matches in S. cerevisiae (SC), D. melanogaster (DM), human (HS), all three combined (ALL), or have no matches in any organism (NO M) evolutionarily conserved genes are more likely to have a phenotype

7. commercial libraries are widely available for most popular organisms

8. Brass AL, …, Elledge SJ. 2008. Science 319: 921-926 RNA interference identifies over 250 host factors required by HIV-1

9. HIV virus HIV virus HIV virus DRUG normal receptor mutant receptor normal receptor human cell human cell human cell susceptible PLUS drug susceptible non-susceptible  DISEASED  HEALTHY  HEALTHY genetic defect in CCR5 chemokine receptor provides immunity against HIV-1 and is/was a model for development of drug therapeutics

10. Griffiths-Jones S, et al. 2008. Nucleic Acids Res 36: D154-D158 RNAi exists because eukaryotic cells make microRNAs of their own

11. active interactions are solid black; inactive interactions are solid gray; weak interactions are thinner lines; gene battery expression inputs to cellular transcriptome are dashed lines; non-neuronal elements have dark blue coloring if present or light blue if absent; neuronal specific elements are likewise colored in shades of reds Makeyev EV, Maniatis T. 2008. Science 319: 1789-1790 the miR-124 regulatory networkgene batteries to global regulators of transcription and alternative splicing

12. how many other RNA mechanisms are remaining to be discovered?!? Amaral PP, …, Mattick JS. 2008. The eukaryotic genome as an RNA machine. Science 319: 1787