Micro RNAs Mechanism in Eukaryotic Cells

Questions and Answers

Where are primary miRNA (pri-miRNA) molecules produced in the eukaryotic cell?

In the nucleus (correct)

In the endoplasmic reticulum

In the cytoplasm

In the mitochondria

Which protein complex is responsible for cleaving the pri-miRNA to produce the precursor miRNA (pre-miRNA)?

Argonaute and RISC

Exportin-5 and Ran-GTP

Drosha and DGCR8 (correct)

Dicer and TRBP

How is the pre-miRNA transported from the nucleus to the cytoplasm?

Passive diffusion

Vesicular transport

Active transport by Exportin-5 and Ran-GTP (correct)

Membrane fusion

What is the length of the pre-miRNA hairpin structure?

60-70 nucleotides Signup and view all the answers

What is the primary mechanism by which miRNAs regulate gene expression in mammals?

mRNA degradation or translational inhibition Signup and view all the answers

Which protein complex is responsible for loading the guide strand of the miRNA into the RNA-induced silencing complex (RISC)?

Argonaute and RISC loading complex Signup and view all the answers

Where does the miRNA guide strand typically bind to its target mRNA?

3' untranslated region Signup and view all the answers

What are the two primary mechanisms by which miRNAs can regulate gene expression in mammals?

Translational inhibition and mRNA deadenylation Signup and view all the answers

Which structural feature do all RNase III enzymes possess?

Both RNase III domain and double stranded RNA-binding domain Signup and view all the answers

How many RNase III domains are present in the Class II RNase III enzyme, Drosha?

2 Signup and view all the answers

Which structural feature of Dicer (Class III RNase III) allows it to bind and cleave the pre-miRNA substrate?

All of the above Signup and view all the answers

How do the structural differences between the various classes of RNase III enzymes relate to their specific functions in the miRNA biogenesis pathway?

They have variations in their domain organization and substrate binding Signup and view all the answers

What is the main principle behind miRNA arrays for identifying and quantifying miRNAs?

Hybridization of labeled miRNAs to complementary oligonucleotides Signup and view all the answers

What is the first step in the miRNA sequencing process?

Purification of the miRNA from total RNA Signup and view all the answers

Which technique allows for the identification of novel miRNAs in a sample?

miRNA sequencing Signup and view all the answers

What is the typical length of the mature miRNA sequence identified by sequencing?

20-25 nucleotides Signup and view all the answers

Approximately how many microRNAs are thought to be encoded by the human genome?

2,000 Signup and view all the answers

What percentage of human genes are predicted to be regulated by microRNAs?

60% Signup and view all the answers

Where are most microRNA genes located in the eukaryotic genome?

In intergenic regions Signup and view all the answers

What is the primary evolutionary advantage of using microRNAs for gene regulation?

Faster response to environmental changes Signup and view all the answers

Which human disease is caused by a mutation in the miR-96 microRNA?

Hereditary progressive hearing loss Signup and view all the answers

Which human disease is caused by a mutation in the miR-184 microRNA?

Keratoconus and cataract Signup and view all the answers

Where can one find information on the known relationships between miRNA dysregulation and human disease?

miRBase Signup and view all the answers

What is the primary mechanism by which alterations in miRNA sequence and expression can contribute to human disease?

Disruption of normal gene regulation Signup and view all the answers

What is one of the primary evolutionary advantages of RNAi mechanisms?

Defense against transposable genetic elements Signup and view all the answers

How do RNAi mechanisms provide protection against viral infections?

By silencing viral mRNAs Signup and view all the answers

What evidence supports the idea that RNAi evolved as a defense mechanism against viruses?

RNAi-deficient plants are more susceptible to viral infections Signup and view all the answers

Which cellular process do RNAi mechanisms help to regulate in order to maintain genome stability?

Transposition of genetic elements Signup and view all the answers

What is the primary method used to induce RNAi-mediated gene silencing in C. elegans?

All of the above Signup and view all the answers

What was the goal of the large-scale RNAi screen performed in C. elegans?

To identify genes involved in fat regulation Signup and view all the answers

What percentage of C. elegans genes were successfully targeted using RNAi in the large-scale screen?

86% Signup and view all the answers

How have the RNAi studies in C. elegans provided insights into human disease?

Many C. elegans genes have human homologs Signup and view all the answers

What type of RNAi-based therapeutic is being developed to silence target genes?

Small interfering RNAs (siRNAs) Signup and view all the answers

What is one of the main delivery methods for RNAi-based therapeutics?

Nanoparticle encapsulation Signup and view all the answers

Which human disease has an RNAi-based therapeutic (Bevasiranib) that has reached clinical trials?

Wet age-related macular degeneration Signup and view all the answers

What is the primary mechanism of action for RNAi-based therapeutics in treating human disease?

Silencing the expression of disease-causing genes Signup and view all the answers

Study Notes

Origin and Mechanism of Micro RNAs

pri-miRNA molecules are produced in the nucleus of eukaryotic cells.
The protein complex Drosha and DGCR8 cleaves pri-miRNA to form precursor miRNA (pre-miRNA).
pre-miRNA is actively transported from the nucleus to the cytoplasm by Exportin-5 and Ran-GTP.
The pre-miRNA hairpin structure is typically 60-70 nucleotides in length.

Regulation of Gene Expression by miRNAs

miRNAs primarily regulate gene expression by causing mRNA degradation or translational inhibition.
The guide strand of miRNA is loaded into the RNA-induced silencing complex (RISC) by Argonaute and RISC loading complex.
miRNAs usually bind to the 3' untranslated region of their target mRNAs.
The two main mechanisms of miRNA action include translational inhibition and mRNA deadenylation.

Domain Structure of RNase III Family Members

RNase III enzymes possess both an RNase III domain and a double-stranded RNA-binding domain (dsRBD).
The Class II RNase III enzyme, Drosha, contains two RNase III domains.
Dicer, a Class III RNase III enzyme, utilizes all structural features (RNase III domains, dsRBD, and PAZ domain) to bind and cleave pre-miRNA.
Variations in domain organization and substrate binding of different RNase III classes relate to their specific functions in miRNA biogenesis.

Identifying miRNAs Using miRNA Arrays and Sequencing

miRNA arrays operate on the principle of the hybridization of labeled miRNAs to complementary oligonucleotides.
The first step in miRNA sequencing involves the purification of miRNA from total RNA.
miRNA sequencing is capable of identifying novel miRNAs in a sample.
The mature miRNA sequence identified by sequencing usually measures 20-25 nucleotides in length.

miRNA Expression in Eukaryotic Genomes and its Impact

Approximately 2,000 microRNAs are encoded by the human genome.
About 60% of human genes are predicted to be regulated by microRNAs.
Most microRNA genes are located in intergenic regions of the eukaryotic genome.
The evolutionary advantage of microRNAs lies in providing a faster response to environmental changes.

miRNA Alterations and Human Disease

A mutation in the miR-96 microRNA can cause hereditary progressive hearing loss.
Mutations in the miR-184 microRNA are associated with keratoconus and cataract.
Information on miRNA dysregulation and human disease can be found in miRBase.
Alterations in miRNA sequence and expression primarily lead to disruption of normal gene regulation.

Evolutionary Reasons for RNAi Mechanisms

RNAi mechanisms primarily offer defense against transposable genetic elements.
They protect against viral infections by silencing viral mRNAs.
Evidence for RNAi's role as a defense mechanism includes the fact that RNAi-deficient plants are more susceptible to viral infections.
RNAi helps regulate the transposition of genetic elements to maintain genome stability.

RNAi in C. elegans for Research

RNAi-mediated gene silencing in C. elegans can be induced through techniques such as microinjection of dsRNA, feeding E. coli expressing dsRNA, or soaking worms in dsRNA solution.
The large-scale RNAi screen aimed to identify genes involved in fat regulation.
86% of C. elegans genes were successfully targeted in the RNAi large-scale screen.
RNAi studies in C. elegans provide insights into human disease due to the presence of homologous genes.

Therapeutic Applications of RNAi

Small interfering RNAs (siRNAs) are being developed as RNAi-based therapeutics to silence target genes.
One of the main delivery methods for these therapeutics is nanoparticle encapsulation.
The RNAi-based therapeutic Bevasiranib has reached clinical trials for wet age-related macular degeneration.
RNAi therapeutics primarily function by silencing the expression of disease-causing genes.

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Description

This quiz tests your understanding of the origin and production mechanism of micro RNAs (miRNAs) in eukaryotic cells. You will explore the locations and protein complexes involved in the cleavage of primary miRNA molecules. Prepare to assess your knowledge on critical aspects of miRNA processing.