Questions and Answers
Where are primary miRNA (pri-miRNA) molecules produced in the eukaryotic cell?
Which protein complex is responsible for cleaving the pri-miRNA to produce the precursor miRNA (pre-miRNA)?
How is the pre-miRNA transported from the nucleus to the cytoplasm?
What is the length of the pre-miRNA hairpin structure?
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What is the primary mechanism by which miRNAs regulate gene expression in mammals?
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Which protein complex is responsible for loading the guide strand of the miRNA into the RNA-induced silencing complex (RISC)?
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Where does the miRNA guide strand typically bind to its target mRNA?
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What are the two primary mechanisms by which miRNAs can regulate gene expression in mammals?
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Which structural feature do all RNase III enzymes possess?
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How many RNase III domains are present in the Class II RNase III enzyme, Drosha?
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Which structural feature of Dicer (Class III RNase III) allows it to bind and cleave the pre-miRNA substrate?
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How do the structural differences between the various classes of RNase III enzymes relate to their specific functions in the miRNA biogenesis pathway?
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What is the main principle behind miRNA arrays for identifying and quantifying miRNAs?
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What is the first step in the miRNA sequencing process?
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Which technique allows for the identification of novel miRNAs in a sample?
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What is the typical length of the mature miRNA sequence identified by sequencing?
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Approximately how many microRNAs are thought to be encoded by the human genome?
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What percentage of human genes are predicted to be regulated by microRNAs?
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Where are most microRNA genes located in the eukaryotic genome?
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What is the primary evolutionary advantage of using microRNAs for gene regulation?
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Which human disease is caused by a mutation in the miR-96 microRNA?
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Which human disease is caused by a mutation in the miR-184 microRNA?
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Where can one find information on the known relationships between miRNA dysregulation and human disease?
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What is the primary mechanism by which alterations in miRNA sequence and expression can contribute to human disease?
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What is one of the primary evolutionary advantages of RNAi mechanisms?
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How do RNAi mechanisms provide protection against viral infections?
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What evidence supports the idea that RNAi evolved as a defense mechanism against viruses?
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Which cellular process do RNAi mechanisms help to regulate in order to maintain genome stability?
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What is the primary method used to induce RNAi-mediated gene silencing in C.elegans?
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What was the goal of the large-scale RNAi screen performed in C.elegans?
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What percentage of C.elegans genes were successfully targeted using RNAi in the large-scale screen?
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How have the RNAi studies in C.elegans provided insights into human disease?
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What type of RNAi-based therapeutic is being developed to silence target genes?
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What is one of the main delivery methods for RNAi-based therapeutics?
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Which human disease has an RNAi-based therapeutic (Bevasiranib) that has reached clinical trials?
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What is the primary mechanism of action for RNAi-based therapeutics in treating human disease?
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Study Notes
Origin and Mechanism of Micro RNAs
- Primary miRNA (pri-miRNA) molecules are produced in the nucleus.
- The protein complex Drosha and DGCR8 cleaves pri-miRNA to produce precursor miRNA (pre-miRNA).
- Pre-miRNA is transported from the nucleus to the cytoplasm via active transport by Exportin-5 and Ran-GTP.
- The pre-miRNA hairpin structure is typically 60-70 nucleotides in length.
Regulation of Gene Expression by miRNA
- miRNAs primarily regulate gene expression in mammals through mRNA degradation or translational inhibition.
- The Dicer and TRBP complex is responsible for loading the guide strand of the miRNA into the RNA-induced silencing complex (RISC).
- The miRNA guide strand typically binds to the target mRNA at the 3' untranslated region (UTR).
- Two primary mechanisms of miRNA action include translational inhibition and mRNA deadenylation.
Domain Structure of RNase III Family Members
- All RNase III enzymes possess the RNase III domain.
- Class II RNase III enzyme, Drosha, contains two RNase III domains.
- Dicer, a Class III RNase III, possesses RNase III domains, a double-stranded RNA-binding domain (dsRBD), and a PAZ domain, which allow it to bind and cleave pre-miRNA substrate.
- Structural differences among RNase III classes lead to functional diversity in miRNA biogenesis.
Identification of miRNAs Using Arrays and Sequencing
- miRNA arrays identify and quantify miRNAs based on hybridization of labeled miRNAs to complementary oligonucleotides.
- The first step in miRNA sequencing is the ligation of 3' and 5' adapters to the miRNA.
- miRNA sequencing allows for the identification of novel miRNAs in a sample.
- The mature miRNA sequence typically identified by sequencing ranges from 20-25 nucleotides.
miRNA Expression and Human Genome Regulation
- The human genome is thought to encode approximately 2,000 microRNAs.
- Around 60% of human genes are predicted to be regulated by microRNAs.
- Most microRNA genes are located in intergenic regions and within protein-coding genes.
- The primary evolutionary advantage of microRNAs is a faster response to environmental changes.
miRNA Alterations Linked to Human Disease
- A mutation in the miR-96 microRNA is associated with hereditary progressive hearing loss.
- A mutation in miR-184 is linked to keratoconus and cataract.
- Information on the link between miRNA dysregulation and human disease can be found in PubMed, miRBase, and OMIM.
- Alterations in miRNA sequence and expression contribute to disease primarily by disrupting normal gene regulation.
Evolutionary Benefits of RNAi Mechanisms
- RNAi mechanisms evolved primarily as a defense against transposable genetic elements.
- RNAi provides protection against viral infections by silencing viral mRNAs.
- RNAi-deficient organisms exhibit increased susceptibility to viral infections, supporting the idea of its role in defense.
- RNAi mechanisms help regulate transposition of genetic elements to maintain genome stability.
RNAi in C.elegans Research
- The primary method for inducing RNAi-mediated gene silencing in C.elegans involves feeding worms E.coli expressing dsRNA.
- The goal of large-scale RNAi screens in C.elegans is to create novel mutant phenotypes for all genes.
- Approximately 70% of C.elegans genes were effectively targeted using RNAi in large-scale screens.
- RNAi studies in C.elegans offer insights into human diseases due to similarities in gene homology.
Therapeutic Applications of RNAi in Human Disease
- RNAi-based therapeutics being developed include small interfering RNAs (siRNAs) and plasmid-encoded shRNAs to silence target genes.
- Main delivery methods for RNAi-based therapeutics include intravenous injection and nanoparticle encapsulation.
- Bevasiranib, an RNAi-based therapeutic, has reached clinical trials for wet age-related macular degeneration.
- The primary mechanism of action for RNAi-based therapeutics is silencing the expression of disease-causing genes.
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Description
Explore the intricate processes of micro RNA biogenesis and their role in gene regulation. This quiz covers the origin, mechanism, and action of miRNAs, including their interaction with mRNA and the enzymes involved. Test your knowledge on how micro RNAs contribute to gene expression in mammals.
