MicroRNA Regulation and Functions

BMSC 320 Nucleic Acids: From Central Dogma to Human Disease

• Nucleic acids play a crucial role in human disease, acting as a bridge from central dogma to human disease.
• Gene silencing involves precursor RNA, dicer, and miRNA leading to mRNA degradation.
• RNA interference (RNAi) uses duplex RNA, dicer, and siRNA for gene silencing.
• Translation inhibition and mRNA degradation are key mechanisms in gene silencing.
• Mismatched miRNA can target more genes, acting as a regulatory mechanism.
• Fully complementary siRNAs mimic some viral infections that use dsRNA, so degradation evolved as a defense mechanism
• Mismatched miRNA can accommodate many more targets and be used as an additional control mechanism to downregulate translation of multiple genes simultaneously

miRNA in Muscle Development

• miR-1 is essential for muscle development.
• Deletion of miR-1-1 in mice leads to lethal heart defects.
• Several miRNA orthologs are involved in muscle development, including miR-27, miR-133, Pax3, Pax7, SRF, IGF-1, PTEN, histone deacetylases, and myomaker protein.

miRNA in Tissue Damage & Repair

• miR-1 and miR-133 regulate heart growth, differentiation, and rhythm.
• miRNA levels in blood show significant changes after heart attacks, implying potential diagnostic applications.
• Altered miRNA expression after heart attacks can indicate the extent of damage and repair processes.
• Research is studying miRNA levels as potential diagnostic tools for various conditions, including infections, liver disease, cancers, and endometriosis.
• miRNA can possibly be used to diagnose and treat cardiac infections.

Up-miRNAs?

• Multiple models/organisms indicate miRNAs can also enhance translation.
• FXR1 is an RNA binding protein associated with the large ribosomal subunit, upregulating translation likely due to ribosome recruitment.
• The mechanisms by which miRNAs upregulate translation remain an area of active research
• Up-regulation of translation is a process involving efficient ribosome recruitment.

The Power of a Good Reporter System

• Eukaryotic plasmid transformed into mammalian cells expresses dual fluorophores.
• The ratio of blue/red fluorescence is measured after miRNA treatment.
• ST6GAL1 3' UTR shows regulation by only 4% of the miRNA library, but effector miRNAs are upregulating by a factor of 3x more.
• The system ensures both fluorescent genes are in the same cell for accurate measurement.

Another Regulator: circRNAs

• circRNAs are covalently closed RNA circles produced during splicing.
• They are typically stable due to lack of ends and resistant to exonuclease degradation.
• They can degrade by endonucleolytic mechanisms, such as DNA-pairing and RNAse H-mediated cleavage.
• circRNAs are often not translatable, but some are functionally relevant.
• Some circRNAs contain genes that backsplice often, thus preventing this regulate other events.
• CircRNA biogenesis can occur through direct back-splicing, intron pairing, and exon skipping

miRNA Sponges: circRNAs

• Many detected circRNAs have multiple miRNA binding sites.
• They can act as competitive inhibitors, limiting miRNA target regulation.
• Expression of a single siRNA can lead to circRNA degradation, releasing a miRNA payload.
• Long non-coding RNAs (lncRNAs) can also act as miRNA sponges.

Summary

• miRNA and siRNA originate from dsRNA intermediates.
• siRNAs are often from viral infections while miRNAs originate from their own genes or mirtrons.
• Pri-miRNA converts to pre-miRNA via microprocessor complexes and is exported.
• miRNA is loaded into RISC to target mRNA, leading to its degradation or silencing.
• This silencing may occur on a full- or partial-match basis.

Integrating Control RNAs into Gene Expression

• DNA methylation and chromatin regulators influence gene expression, potentially impacting downstream processes like transcription and translation.
• miRNA and circRNA influence the translation process for mRNA to protein.
• Many gene products can be regulated by similar regulators in a defined sequence.
• Chromatin regulators, DNA methylation, transcriptional activators, transcriptional repressors, splicing factors, and siRNAs, IncRNAs, and circRNAs each play a role in gene expression regulation.

Explore the complex roles of miRNAs in gene regulation, muscle development, and responses to cellular stress. This quiz covers key concepts like the seed region, miRNA sponges, and factors involved in skeletal muscle growth. Test your knowledge on how miRNAs influence biological processes and the implications in health and disease.