Presentation on theme: "Dogmatic View of Gene Expression DNAProteinRNA Post-transcriptional Control: Quantitative Control: Levels of mRNA not proportional to levels of mRNA synthesized."— Presentation transcript:
Dogmatic View of Gene Expression DNAProteinRNA Post-transcriptional Control: Quantitative Control: Levels of mRNA not proportional to levels of mRNA synthesized or protein produced Qualitative Control: More than one protein from a single gene (e.g. Differential RNA Processing or RNA editing)
An RNA-Centric View of Gene Expression RNA DNA Protein
Non Coding RNAs: RiboRegulators (~97% of RNAs Present in Human Cells are Non-Coding) rRNA tRNA snRNAs snoRNAs Guide RNA Catalytic: Ribozymes Telomerase Introns 5 UTR 3 UTR Vault Y RNAs 7SK Xist, H19 MicroRNAs Viral RNAs Retrotransposons
Non Coding RNAs: SnoRNAs Large Family Intron-encoded Guide RNA Modification
Non Coding RNAs: Telomerase RNA Component of telomerase Provides template for telomere synthesis Role in Cancer and Aging
RNA-Mediated Gene Silencing Post-transcriptional Gene Silencing (PTGS) or RNA Interference (RNAi) Transcriptional Gene Silencing (TGS) (RNA-dependent DNA Methylation) Gene Silencing By MicroRNAs
Discovery of RNAi Double-stranded RNA inject C. elegans Neg. control Uninjected Antisense RNA dsRNA sense antisense Nature 1998 391:806-811 Mex-3 mRNA detection in embryos by in situ hybridization
Remarkable Properties of RNAi dsRNA (not ssRNA) is interfering agent Sequence-specific loss of mRNA and protein Effective against exons not introns Potent (few dsRNA molecules/cell effective) Persistent (affects next generation) Effects can cross cell barriers (feed, soak)
RNAi in Mammalian Cells Long dsRNA triggers global (non-specific) gene-silencing (i.e. interferon response) Breakthrough: Short dsRNA (~22 nt) induces RNAi Nature 2001 411: 494-498 Silencing of lamin proteins in human cells by dsRNA transfection
RNA-Mediated Gene Silencing RNA Interference Cosuppression by transgenes in plants Quelling in Fungi Transcriptional Gene Silencing (TGS) Common Trigger:
RNAi Applications GENETIC TOOL GENE THERAPY Probing Gene Function Combat Viral Infection Treat Genetic Diseases (New expression strategies)
What is the Purpose of RNA-Mediated Gene Silencing?
Proposed Biologic Roles Antiviral Defense Suppress Transposon Activity Response to Aberrant RNAs Gene Regulation (e.g. MicroRNAs) Immune System of the Genome
MicroRNAs: Expanding Family of RiboRegulators lin-4 and let-7 RNAs (from worm) were first examples Also known as stRNAs (small temporal RNAs) Regulate expression of proteins and developmental timing Tip of the iceberg………..MicroRNAs are everywhere!