Learning Objectives

• Differentiate between Knock-out and Knock-in strategies.
• Compare the mechanisms of miRNA and siRNA in gene silencing.
• Identify the clinical significance of RNA interference in malignancy.

1. Transgenic Strategies

Modifying the mouse genome allows researchers to study the function of specific genes in a living organism. There are two primary insertion methods:

• Random Insertion: The gene is inserted anywhere in the genome, often resulting in constitutive expression (the gene is always “on”).
• Targeted Insertion: Achieved through homologous recombination with a specific mouse gene. This often allows for conditional expression (the gene can be turned on or off in specific tissues or at specific times).

Knock-out: Removing a gene to study the effects of its absence.
Knock-in: Inserting a new gene into the genome.

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2. RNA Interference (RNAi)

This is a natural process where small non-coding RNA molecules target mRNAs to inhibit gene expression before translation can occur.

MicroRNA (miRNA)

• Origin: Naturally produced by the cell as hairpin structures.
• Binding: Uses loose nucleotide pairing, allowing it to broadly target many related mRNAs.
• Effect: Blocks mRNA translation and may facilitate its degradation.
• Clinical Link: Abnormal miRNA expression can contribute to malignancy (e.g., if a miRNA silences a tumor suppressor gene).

Small Interfering RNA (siRNA)

• Origin: Usually derived from an exogenous dsRNA source (e.g., a virus).
• Binding: Requires complete nucleotide pairing, making it highly specific for a single mRNA target.
• Effect: Results in mRNA cleavage before translation.
• Research Use: Often chemically synthesized for “knock-down” experiments to temporarily reduce gene expression.

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