ERT2 refers to a modified version of the human estrogen receptor used in molecular biology and genetics, particularly for controlling gene expression in specific tissues or at specific times.
Here's a more detailed explanation:
Cre-ERT2 System Explained
The Cre-ERT2 system is a powerful tool for conditional gene knockout or activation in living organisms. It consists of two main components:
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Cre Recombinase: An enzyme derived from bacteriophage P1 that catalyzes the site-specific recombination of DNA between loxP sites (specific DNA sequences). When Cre recombinase recognizes loxP sites flanking a target gene, it excises that gene from the DNA.
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ERT2 (Estrogen Receptor T2): This is a modified version of the human estrogen receptor. The key modification is that ERT2 does not bind to the natural estrogen ligand (17β-estradiol) at normal physiological concentrations. Instead, it binds to synthetic ligands like 4-hydroxytamoxifen (OHT), also known as tamoxifen.
How the Cre-ERT2 System Works
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Constructing the System: Researchers genetically engineer animals (typically mice) with two components:
- A "floxed" gene: The gene of interest is flanked by loxP sites (i.e., it's "floxed").
- Cre-ERT2 fusion protein: Cre recombinase is fused to the ERT2 domain, which is expressed under the control of a specific promoter, limiting its expression to particular tissues or cell types.
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In the Absence of Tamoxifen: The Cre-ERT2 fusion protein remains inactive in the cytoplasm. The ERT2 domain prevents Cre recombinase from entering the nucleus and acting on the loxP sites.
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Induction with Tamoxifen: When tamoxifen (or another suitable ERT2 ligand) is administered, it binds to the ERT2 domain. This binding causes a conformational change in the Cre-ERT2 protein, allowing it to translocate into the nucleus.
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Gene Recombination: Once in the nucleus, Cre recombinase recognizes the loxP sites flanking the target gene and excises (removes) the DNA sequence between them. This can result in a knockout of the gene's function if the excised sequence is crucial for its expression or protein production. Alternatively, the system can be used to remove a "stop" sequence preventing expression of a downstream gene, thereby activating that gene upon tamoxifen administration.
Applications of the Cre-ERT2 System
The Cre-ERT2 system is widely used in biological research for:
- Conditional Gene Knockout: Inactivating genes in specific tissues or at specific developmental stages.
- Conditional Gene Activation: Activating genes in a controlled manner.
- Lineage Tracing: Marking cells and their descendants that have expressed Cre recombinase at some point in time.
- Studying Gene Function: Understanding the role of genes in development, disease, and other biological processes.
In summary, ERT2 is a crucial component of the Cre-ERT2 system, enabling researchers to control gene expression with high spatial and temporal precision.
