Lecture Summary:
This lecture focuses on microRNAs (miRNAs), a class of non-coding RNAs crucial for regulating gene expression. It discusses their biogenesis, mechanisms of action, role in gene regulatory networks, tissue-specific expressions, impact on diseases like cancer, and experimental approaches for their study.
Key Points from the Lecture:
Introduction to MicroRNAs
- MicroRNAs are non-coding RNAs that regulate gene expression.
- They influence various biological processes including organ development and disease pathways like cancer.
MicroRNA Biogenesis
- Transcription: MicroRNAs are transcribed from dedicated genes in the genome.
- Primary miRNA Transcript: The initial product is a primary miRNA transcript.
- Enzymatic Processing:
- Drosha and DGCR8/Pasha: These enzymes process primary miRNA transcripts into pre-microRNA.
- Exportin 5 Complex: Transports pre-microRNA from the nucleus to the cytoplasm.
- Dicer: In the cytoplasm, Dicer further processes pre-microRNAs to create mature miRNA strands.
- RISC Loading:
- Mature miRNAs are loaded into the RNA-induced silencing complex (RISC).
- Typically, only one strand is loaded into the RISC.
- It binds to specific regions of mRNA, often leading to mRNA degradation.
Mechanisms of Gene Regulation by MicroRNAs
- Degradation of mRNA: The primary mechanism where miRNA-RISC complex leads to mRNA breakdown.
- Inhibition of Translation: In some cases, miRNAs prevent the translation of mRNAs without causing mRNA degradation.
Specificity and Expression of MicroRNAs
- MicroRNAs are often cell type-specific and tissue-specific, which allows precise regulation of gene expression in diverse cellular contexts.
- They can bind primarily to the 3' untranslated region (UTR) of mRNA and less commonly to the 5' UTR.
Role of MicroRNAs in Cellular Differentiation
- MicroRNAs can influence cell fate decisions, such as in stem cell differentiation into different cell types like neurons or epithelial cells.
- By suppressing specific master regulator transcription factors, microRNAs can control the dominance of gene expression modules that dictate cell differentiation.
MicroRNAs in Disease
- Specific microRNAs are found in secreted body fluids like cerebrospinal fluid and play roles in regulating processes such as the quiescence of neuronal stem cells.
- Altered microRNA levels are observed in various diseases, including cancer, indicating their potential in disease diagnostics and therapeutics.
Experimental Methods for Studying MicroRNAs
- Small RNA Sequencing: Comprehensive but expensive method to study many miRNAs.
- Quantitative Real-Time PCR: Cost-effective for studying specific miRNAs with high sensitivity.
- Fluorescence In Situ Hybridization (FISH): Determines the localization of miRNAs in cells.
- Reporter Assays: Used to study miRNA function by observing the impact on reporter genes like GFP when linked to miRNA target sequences.
Conclusion
This lecture covered essential aspects of microRNA biology and their vast implications in gene regulation and cell biology, providing foundational knowledge for further studies in genetics and molecular biology.