transcriptomics

Detection of mRNAs in Time and Space

  • Understanding gene expression regulation requires assessing where and when RNAs are expressed.

  • Techniques for studying RNA expression:

    • cDNA Synthesis: Reverse transcriptase is used to synthesize complementary DNA (cDNA) from mRNA.

    • PCR Amplification: Polymerase Chain Reaction (PCR) amplifies the cDNA to examine RNA expression levels.

    • Gel Electrophoresis: Separated RNA can be visually assessed in relation to different cellular tissues.

Techniques for RNA Detection

  • Northern Blotting:

    • Method for detecting specific mRNA levels.

    • Involves gel electrophoresis of RNA, transfer to a membrane, and hybridization to a labeled DNA probe.

    • Provides a semiquantitative measure of mRNA levels.

  • In Situ Hybridization:

    • Allows for localization of mRNAs within tissues without destroying the spatial context.

    • Involves using fluorescent probes to visualize mRNA distribution in cells.

    • Variations of this technique may include colored precipitation products for visualization under a microscope.

  • Quantitative PCR (q-PCR):

    • Provides real-time quantitative analysis of mRNA expression levels.

    • Uses cDNA synthesis followed by amplification with specific primers and detection through fluorescence which quantifies the amount of target sequence.

    • Distinguishes it from RT-PCR which is not quantitative.

Analysis of Thousands of Genes Simultaneously

  • Techniques to assess multiple gene expressions concurrently include:

    • DNA Microarrays:

      • A chip with spots representing thousands of different genes.

      • cDNAs from different sources (like brain and liver cells) are labeled with different fluorescent dyes.

      • By mixing and applying the labeled cDNAs to the microarray, gene expression in the cell populations can be compared.

      • Color coding indicates preferential expression, similarity, or lack of expression of genes across cell types.

    • RNA Sequencing (RNAseq):

      • A high-throughput method to analyze gene expression profiles without the limitations of microarrays.

      • Involves sequencing cDNAs directly to quantify gene expression across the entire transcriptome.

      • Able to detect variations like single nucleotide polymorphisms and alternative splicing forms.

      • Plays a significant role in projects like the Human Cell Atlas for characterizing transcriptomic diversity in human cells.

Proteins Can Be Studied Using Electrophoresis

  • SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE):

    • Method for separating proteins based on size.

    • Proteins are denatured with SDS and heat to disrupt interactions and apply a negative charge.

    • When an electric current is applied, smaller proteins move faster through the gel, allowing size-based separation.

    • Gels are stained to visualize proteins, aiding in mixture characterization.