Long-range disruption of gene expression by a selectable marker cassette

Area of Science:

• Molecular Biology
• Genetics
• Gene Regulation

Background:

• Selectable marker cassettes, such as PGK-Neo, are commonly used in gene targeting.
• Retention of these cassettes in targeted loci can lead to unintended gene expression alterations.
• Previous studies suggest potential disruption of neighboring gene expression.

Purpose of the Study:

• To investigate the impact of PGK-Neo cassette insertion on gene expression in multigene clusters.
• To examine long-distance effects of targeted mutations within the granzyme B and beta-like globin gene clusters.
• To understand the regulatory interactions disrupted by selectable markers.

Main Methods:

• Targeted mutation of the granzyme B gene cluster using PGK-Neo.
• Targeted mutation of the beta-globin locus control region (LCR) using PGK-Neo.
• Analysis of gene expression changes in neighboring genes within the affected loci.
• Comparison with a targeted mutation of the cathepsin G gene.

Main Results:

• PGK-Neo insertion in the granzyme B locus reduced expression of multiple genes over 100 kb away.
• PGK-Neo insertion into the beta-globin LCR abolished downstream globin gene expression.
• Targeted mutation of the cathepsin G gene had minimal impact on upstream gene expression.
• The PGK-Neo cassette appears to be captured by the regulatory domain, disrupting normal interactions.

Conclusions:

• Selectable marker cassettes like PGK-Neo can have significant, long-distance effects on gene expression within multigene clusters.
• These cassettes can interfere with locus control regions and tissue-specific gene regulation.
• Careful consideration of marker cassette placement is crucial for accurate gene targeting studies.