Lab 9: Gene Expression Analysis, qPCR, and RNA Extraction in HGPS

Experimental Overview: Progerin and HGPS Phenotypes

• Lab Context:

  • Lab Session: Lab 9 – Examine Sequencing & Extract RNA (Dated 11.4.26 / 11.4.96).
  • Overarching Experimental Question: Does Progerin alter gene expression in the confirmed cell line in a manner consistent with the known phenotypes observed in individuals with Hutchinson-Gilford Progeria Syndrome (HGPS)?

• HGPS Molecular Phenotypes and Candidate Genes:

  • HGPS is associated with a wide variety of characteristic molecular phenotypes. The expression levels of specific genes associated with each phenotype are systematically tested:
  • Disorganized Nuclear Architecture: Evaluated by testing the expression of $SUN1$.
  • Dysregulated Chromatin Organization: Evaluated by testing the expression of $EZH2$.
  • Alteration of Signaling Pathways: Evaluated across multiple distinct cellular stress and signaling axes:
    • Inflammation: Evaluated through $IL6$.
    • DNA Damage: Evaluated through $TP53$ and $CDKN1A$.
    • Metabolism / Energy Usage: Evaluated through $TFAM$ and $HMOX1$ (noted as $MMOX1$).
    • Cellular Stress: Evaluated through $ATF4$ and $HSPA5$.
  • Cellular Senescence: Evaluated via phenotypes of altered self-renewal:
    • Altered Self-Renewal: Evaluated through $CDKN2A$.

• Novelty and Experimental Rationale:

  • The baseline expression of these specific candidate genes has not been previously characterized in these particular HGPS cell lines.
  • It is currently unknown whether the expression of these genes will be altered by progerin overexpression or remain unaffected.

Gene Expression Profiling: Transcript vs. Protein Level

• Stages of the Central Dogma and Corresponding Analytical Techniques:
  • The Central Dogma pathway dictates information flow: $\text{DNA} \xrightarrow{\text{Transcription}} \text{RNA} \xrightarrow{\text{Translation}} \text{Protein}$.
  • DNA Level: Examined using Sanger Sequencing to verify sequence integrity and mutations.
  • RNA (Transcript) Level: Evaluated using Quantitative PCR ($\text{qPCR}$), which represents the immediate experimental stage of this protocol.
  • Protein Level: Assessed downstream via Western Blotting.

Quantitative PCR (qPCR) Methodology and Experimental Controls

• Definition and Function of qPCR:

  • Quantitative PCR ($\text{qPCR}$, also termed Real-Time PCR) is a PCR-based technique that directly couples the enzymatic amplification of a target RNA sequence with quantification (the "$q$" in qPCR) of the total amount of RNA molecules in real time.
  • It enables sensitive, precise measurement of RNA transcript abundance for specific genes of interest.

• Experimental Comparison and Controls:

  • Expression levels of target genes are compared between two distinct experimental conditions:
  • $\text{DOX}-$: Doxycycline-negative control cells lacking progerin expression.
  • $\text{DOX}+$: Doxycycline-positive experimental cells undergoing progerin overexpression.
  • Any significant differences or alterations in RNA expression detected between $\text{DOX}-$ and $\text{DOX}+$ conditions can be directly attributed to the physiological impact of progerin on cellular phenotype.

Chemical Properties of RNA and Enzymatic Degradation Hazards

• Physical and Chemical Vulnerabilities of RNA:

  • RNA exists predominantly as a single-stranded nucleic acid.
  • It is chemically unstable compared to double-stranded DNA.
  • It is highly prone to rapid degradation by ribonucleases (RNases).

• Nature and Threat of RNases:

  • RNases are hydrolytic enzymes that catalyze the cleavage of phosphodiester bonds linking ribonucleotides in RNA molecules.
  • RNases are ubiquitous throughout the environment, on lab surfaces, skin, and within airborne particulates.
  • RNase contamination constitutes the primary hazard and obstacle to any experimental workflow involving RNA isolation and analysis.

Protocols and Strategies for RNase Mitigation

• Three Primary Anti-RNase Countermeasures:
  • 1. TRIzol Application During Extraction:
  • TRIzol is a potent, toxic chemical reagent applied during cell lysis.
  • It denatures all cellular proteins—including endogenous and exogenous RNases—rendering them nonfunctional to protect RNA from enzymatic digestion during extraction.
  • 2. Low-Temperature Incubation (Ice):
  • RNA samples must be placed immediately on ice once eluted.
  • Ice reduces the thermal energy of the solution, lowering temperatures well below the enzymatic optimum required for RNase activity and dramatically slowing any residual catalytic breakdown.
  • 3. RNase decontamination with RNaseZAP:
  • RNaseZAP is a surface-decontaminating chemical solution used to eliminate environmental RNases.
  • It actively denatures and degrades RNases on contact across work areas, pipettes, and labware before and after RNA isolation.

Column-Based RNA Extraction and Genomic DNA Removal

• Silica-Based Spin Column Chromatography:

  • Silica matrix columns possess a biochemical binding affinity for all nucleic acid polymers under high salt/chaotropic conditions, binding RNA as well as DNA.
  • The silica column provides an inherent protective effect for RNA during isolation: proteins (such as RNases) cannot bind to the silica matrix.
  • If an RNase enters the spin column during the initial sample loading, it remains in the flow-through and is washed away before elution.
  • Standard Column Steps:
  • $\text{Bind} \rightarrow \text{Wash} \rightarrow \text{Elute}$

• Modification: Genomic DNA Removal via Enzymatic Digestion:

  • In a manner analogous to plasmid minipreps where host bacterial genomic DNA must be eliminated, column-based total RNA isolation requires removal of host cellular genomic DNA.
  • Because silica membranes bind all nucleic acids non-selectively, genomic DNA co-binds to the column along with the RNA.
  • To guarantee pure RNA isolation without DNA interference in downstream qPCR, the column matrix is incubated with DNase I.
  • DNase I: An endonuclease that selectively cleaves and degrades DNA molecules without degrading or disrupting single- or double-stranded RNA.