Advanced Transcriptomics, Cloning, and Genetic Engineering Strategies

Characterizing the Transcriptome: Advanced Techniques

  • Transcriptome Analysis via Sequencing:     * Comprehensive transcriptome analysis is enabled through two primary forms of RNA sequencing (RNAseq):         * Bulk RNA Sequencing (RNAseq): Used for analyzing the sum of gene expression across a large population of cells.         * Single-cell RNA Sequencing (scRNAseq): Allows for the analysis of gene expression at the level of individual cells, providing a higher resolution of the cellular heterogeneity within a sample.

  • Fluorescence In Situ Hybridization (FISH):     * Mechanism: This technique utilizes labeled nucleic acids (probes) to hybridize with specific target sequences.     * Application: It is used to visualize the spatial distribution of transcripts within a cell, tissue, or whole organ.     * Examples of Use:         * Creating a cell-by-cell map of the entire mouse brain.         * Visualizing specific gene expression patterns in situ, as seen in research involving spatial transcriptomics and bioanalytical methods.

Cloning and Recombinant DNA Technology

  • Types of Cloning:     * Reproductive and Therapeutic Cloning:         * These processes involve nuclear transfer.         * Reproductive cloning aims to produce a whole organism (e.g., Dolly the sheep, credited to Sir John Gurdon’s foundational work in nuclear transfer).         * Therapeutic cloning focuses on creating embryonic stem cells for medical treatment.     * Gene Cloning:         * Involves creating identical copies of specific genes or segments of DNA.

  • Production of Recombinant DNA:     * Definition: Recombinant DNA refers to a combination of DNA fragments derived from different sources, which are often different organisms.     * The Process of DNA Cloning:         1. Selection of Vector: DNA fragments are typically inserted into a bacterial DNA plasmid.         2. Characteristics of Plasmids: Plasmids are circular, double-stranded DNA molecules used as cloning vectors.         3. Cleavage: The circular plasmid DNA is cut (cleaved) using a restriction enzyme.         4. Insertion: The DNA fragment to be cloned is introduced into the cut site of the plasmid.         5. Covalent Linkage: The enzyme DNA ligase creates covalent bonds to join the DNA fragment to the plasmid, resulting in a recombinant DNA molecule.         6. Microscopy Detail: The size and structure of these plasmids can be observed via micrographs (e.g., images showing plasmids at a scale of $200\,nm$, courtesy of Huntington Potter and David Dressler).

  • Replication of Recombinant Plasmids:     * The double-stranded recombinant plasmid DNA is introduced into a bacterial cell.     * Within a cell culture, the bacteria reproduce to create hundreds of millions of new bacteria, each carrying the recombinant plasmid.     * Many copies of the purified plasmid can then be isolated from the bacteria after they are lysed (broken open).

Genetic Engineering Strategies: Plasmids

  • Overexpression of Proteins:     * Plasmids are utilized to force a cell to produce large quantities of a protein of interest.     * Example: Biomanufacturing of Insulin: Using recombinant DNA in bacteria to produce human insulin for medical use.

  • Cellular Re-engineering and Reprogramming:     * Hepatocyte to Neuron Conversion: Plasmids carrying Neuron-Specific Transcription Factors (TRs) can be used to "re-engineer" hepatocytes (liver cells) into neurons.     * Induced Pluripotent Stem Cells (iPSCs): Adult cells can be "reprogrammed" using plasmids to create iPSCs, which have the potential to become any cell type in the body.

  • Reporter Proteins:     * Engineering a cell with reporter proteins is essential for understanding expression patterns.     * Example: Using Green Fluorescent Protein (GFP) as a reporter in specific neurons of a fruit fly larva to track where and when a gene is active.

Genetic Engineering Strategies: CRISPR-Cas9

  • Precise Genome Editing:     * The CRISPR system is a bacterial-derived mechanism used to edit genes with high precision.     * Key Components:         * Cas9 Protein: An enzyme that acts as molecular scissors to cut DNA.         * Guide RNA (gRNA): A sequence that directs the Cas9 protein to a specific $3'$ or $5'$ location on the double-stranded DNA in the genome.     * Mechanism of Action:         1. Cas9 creates a double-strand break at a specific cleavage site.         2. Homologous Recombination: A target gene can be replaced by an altered version provided by genetic engineering. The cell's repair machinery uses the altered version to fix the break, thereby integrating the new sequence.

  • Applications of Genome Engineering:     * Medicine: Gene surgery and drug development.     * Biology: Studying genetic variation and creating animal models for research.     * Biotechnology: Developing new fuels, advanced materials, and improved food sources.

Administrative Agenda and Upcoming Action Items

  • In-Class Content:     * Guest Lecturer: Hailey McCoy-Munger (BSE/MS in BME, graduate student in the Worthington Lab) will present an "Overview of the Cytoskeleton" on Wednesday, April 15 ($4.15$).     * Survey: A feedback survey regarding the guest lecture is due Friday, April 17 ($4.17$). Completion contributes to Participation & Professionalism grades.

  • Laboratory Schedule:     * Lab 4 (DNA Fingerprinting): Conducted during the week of April 14 or 16.     * Lab 5 (CRISPR Gene Editing): Conducted during the week of April 21 or 23.     * Lab Report C: Covers Lab 4; due Friday, May 8 at $11:59\text{pm}$.

  • Homework:     * Homework 4: Details coming soon; due Sunday, April 26 at $11:59\text{pm}$.

  • Exams:     * Exam 3: Scheduled for Wednesday, May 13 at $10:00\text{am}$.

  • Credits:     * Featured Image: "The Hidden Dance of Plant Fertilization" by Yoko Mizuta, Nagoya University.