microRNA physiological significance cellular differentiation development post-transcriptional gene regulation Nobel 2024

microRNA biogenesis pathway RISC gene silencing diagram

A handwritten medical physiology exam answer on white ruled notebook paper, written in blue ink in a neat student handwriting style. The content reads: "2024 NOBEL PRIZE - PHYSIOLOGY OR MEDICINE Victor Ambros & Gary Ruvkun Discovery of microRNA & Post-Transcriptional Gene Regulation INTRODUCTION microRNAs (miRNAs) are short, single-stranded, non-coding RNA molecules of 21-23 nucleotides. Discovered in 1993 using C. elegans model organism. First miRNA: lin-4 (Ambros) - found to regulate lin-14 gene. Second miRNA: let-7 (Ruvkun) - evolutionarily conserved across species. >1000 miRNA genes identified in human genome. Each miRNA can regulate hundreds of target mRNAs. BIOGENESIS OF miRNA (Brief) DNA → pri-miRNA (transcription, RNA Pol II) Nucleus: Microprocessor complex (Drosha + DGCR8) → pre-miRNA (70 nt, hairpin) Cytoplasm: Dicer enzyme → mature miRNA duplex (21-23 nt) Loaded into RISC (RNA-Induced Silencing Complex) → mRNA degradation OR translational repression [Page 1/4]" The handwriting is clear, uses underlining for headings, has slight natural variation, written on blue-lined notebook paper.

A handwritten medical physiology exam answer on white ruled notebook paper, written in blue ink in neat student handwriting. The content reads: "PART A: PHYSIOLOGICAL SIGNIFICANCE OF miRNAs IN CELLULAR DIFFERENTIATION AND DEVELOPMENT (5 Marks) 1. TEMPORAL CONTROL OF DEVELOPMENT - lin-4 miRNA represses lin-14 → controls timing of larval stage transitions (L1→L4) in C. elegans - let-7 miRNA represses lin-41 → ensures correct adult stage differentiation - miRNAs act as 'developmental timers' switching cell identity at right time 2. STEM CELL MAINTENANCE & DIFFERENTIATION - miR-302/367 cluster maintains embryonic stem cell (ESC) pluripotency - miR-34 promotes differentiation; miR-145 represses OCT4/SOX2/KLF4 (pluripotency factors) - Differentiation requires sequential activation of specific miRNAs - Without miRNAs (Dicer knockout): embryo fails to develop → embryonic lethal 3. NEURAL DIFFERENTIATION - miR-124: most abundant brain miRNA; promotes neuronal differentiation → Represses REST (neural gene suppressor) → allows neuron-specific genes to be expressed - miR-9: regulates neural progenitor proliferation vs. differentiation balance - miR-132: synaptic plasticity and dendritic growth [Page 2/4]" Written in neat blue ink on lined notebook paper with slight natural handwriting variation, headings underlined.

A handwritten medical physiology exam answer on white ruled notebook paper, written in blue ink in neat student handwriting. The content reads: "PART A (continued): Physiological Significance of miRNAs 4. CARDIAC & MUSCLE DEVELOPMENT - miR-1 & miR-133: cardiac and skeletal muscle differentiation → miR-1: promotes muscle gene expression, suppresses non-muscle genes → miR-133: regulates cardiomyocyte proliferation - Absence of miR-1-2 in mice → ventricular septal defects - miR-208: cardiac hypertrophy regulation (encoded within MHC gene) 5. HEMATOPOIETIC DIFFERENTIATION (Blood Cell Development) - miR-181: promotes B-lymphocyte differentiation - miR-155: T-cell immunity and B-cell function - miR-150: regulates megakaryocyte-to-platelet transition - miR-223: granulocyte differentiation; myeloid lineage commitment 6. ORGAN DEVELOPMENT & PATTERNING - miR-196: Hox gene regulation → limb patterning - miR-430 (zebrafish): clears maternal mRNA at embryo activation - miR-17~92 cluster: lung branching morphogenesis - DICER1 mutations (enzyme that processes pre-miRNA) → DICER1 syndrome: Multinodular goiter, pleuropulmonary blastoma, Wilms tumor SUMMARY BOX - Part A: miRNAs act as FINE-TUNERS of gene expression during development. They ensure: Right gene, Right cell, Right time ~60% of human protein-coding genes are regulated by miRNAs [Page 3/4]" Written in neat blue ink on lined notebook paper, headings underlined with a ruler, small box drawn around the summary section.

A handwritten medical physiology exam answer on white ruled notebook paper, written in blue ink in neat student handwriting. The content reads: "PART B: HOW miRNA DISCOVERY EXPANDED OUR UNDERSTANDING OF GENE REGULATION BEYOND TRANSCRIPTIONAL CONTROL (5 Marks) CLASSICAL VIEW OF GENE REGULATION (Pre-miRNA Era): DNA → (Transcription factors) → mRNA → Protein Gene regulation was thought to occur ONLY at transcriptional level (promoters, enhancers, transcription factors - 'one gene, one protein' concept) THE PARADIGM SHIFT - Post-Transcriptional Control: miRNA discovery revealed a NEW layer of regulation AFTER transcription: 1. POST-TRANSCRIPTIONAL SILENCING MECHANISM - miRNA binds 3'-UTR of target mRNA with imperfect complementarity - Outcome 1: Translational repression (ribosome stalling) - Outcome 2: mRNA deadenylation → decapping → degradation - One miRNA can regulate MULTIPLE mRNAs (gene networks, not just single genes) - One mRNA can be regulated by MULTIPLE miRNAs (combinatorial control) 2. EXPANSION BEYOND 'CENTRAL DOGMA' - Central dogma: DNA → RNA → Protein - miRNA adds: DNA → RNA → [miRNA regulation] → ↓Protein - Non-coding RNA is NOT 'junk' - it has regulatory function - ~98% of transcribed human genome is non-coding; miRNAs are a major functional class [Page 4/4 - continued overleaf]" Written in neat blue ink on lined notebook paper, headings underlined, arrows drawn with pen.

A handwritten medical physiology exam answer on white ruled notebook paper, written in blue ink in neat student handwriting. The content reads: "PART B (continued): Expanded Understanding of Gene Regulation 3. EPIGENETIC & MULTI-LEVEL REGULATORY INTEGRATION - miRNAs regulate transcription factors → indirect transcriptional effects - miRNAs interact with epigenetic machinery (DNA methylation, histone modification) - e.g. miR-29 targets DNMT3a/3b → controls DNA methylation patterns - Creates feedback loops: TF activates miRNA → miRNA suppresses TF's own targets 4. CONCEPT OF 'GENE REGULATORY NETWORKS' - Before miRNA: gene regulation was linear (one TF → one gene) - After miRNA: gene regulation is a NETWORK (many-to-many relationships) - miRNAs buffer gene expression noise → canalization of development - miRNAs fine-tune protein output without changing mRNA transcription rate 5. CLINICAL & DISEASE IMPLICATIONS (expansion of understanding) Disease | miRNA involved Cancer | miR-21 (oncomiR), miR-34 (tumor suppressor) Heart disease | miR-208, miR-1, miR-133 Congenital deafness | mutations in miRNA genes Eye disorders | miR-204, miR-211 Viral immunity | miR-122 (Hep C), miR-155 (influenza) 6. THERAPEUTIC POTENTIAL - NEW FRONTIERS - miRNA mimics: replace lost tumor-suppressor miRNAs - Antagomirs (anti-miRNA): block overactive oncomiRs - Miravirsen: anti-miR-122 drug for Hepatitis C (first clinical trial) - miRNAs as circulating biomarkers in blood (liquid biopsy for cancer/MI) CONCLUSION: miRNA discovery revealed that gene expression is regulated at multiple levels - transcriptional, post-transcriptional, translational, and epigenetic. It transformed our view from a simple 'on-off switch' to a complex, tunable, multi-layered regulatory system. [Nobel Prize 2024 - Ambros & Ruvkun] [Page 5/5 - END]" Written in neat blue ink on lined notebook paper, table drawn with pen/ruler, headings underlined, conclusion in a box.

Handwritten medical exam answer on lined notebook paper in blue ink, neat student handwriting. Title: "PART B continued - Expanded Gene Regulation". Content covers: epigenetic integration of miRNAs with DNA methylation (miR-29 targets DNMT3a), gene regulatory networks showing many-to-many miRNA-mRNA relationships, a small table listing diseases and their miRNAs (cancer: miR-21, heart: miR-208, hearing loss: miRNA mutations), therapeutic applications (antagomirs, miRNA mimics, Miravirsen for Hepatitis C), and a boxed conclusion stating that miRNA discovery revealed multi-layered gene regulation beyond transcription, transforming simple on-off switch concept to a complex tunable system. Nobel 2024 Ambros and Ruvkun. Page 5 of 5. Headings underlined.

A hand-drawn diagram on white paper in blue and black pen, resembling a student's notebook sketch for a medical physiology exam. The diagram shows the miRNA biogenesis pathway with the following labeled steps drawn as simple sketches: At the top: DNA double helix labeled "miRNA gene" with arrow labeled "RNA Pol II" pointing down to "pri-miRNA" (long wavy line with hairpin loop). In a shaded box labeled "NUCLEUS": Drosha + DGCR8 complex (shown as oval shape) cutting pri-miRNA into "pre-miRNA" (stem-loop hairpin structure, ~70 nt). Arrow labeled "Exportin-5" pointing out of nucleus box downward. In area labeled "CYTOPLASM": Dicer enzyme (rectangle) processing pre-miRNA into "miRNA:miRNA* duplex" (two parallel lines). Arrow to "RISC loading" (AGO2 protein shown as circle). One strand discarded (labeled "passenger strand *"), other strand labeled "guide strand". Final RISC-miRNA complex binds to mRNA 3'-UTR. Two outcome arrows: left arrow to "mRNA DEGRADATION" (wavy line with X), right arrow to "TRANSLATIONAL REPRESSION" (ribosome blocked with stop sign). Title at top: "miRNA BIOGENESIS PATHWAY" underlined. Simple clean educational diagram style.