Conservative site-specific and single-copy transgenesis in human LINE-1 elements.

Area of Science:

• Molecular Biology
• Genetics
• Biotechnology

Background:

• Genome engineering is crucial for biotechnology and medicine, but current methods face challenges like cytotoxicity and limited cargo capacity.
• Phage lambda integrase (Int) facilitates conservative site-specific DNA integration, offering a potential tool for precise genome modification.

Purpose of the Study:

• To develop a novel genome engineering tool for precise, large-scale transgene insertion into human cells.
• To evaluate the safety and efficacy of integrating large DNA payloads into Long INterspersed Elements-1 (LINE-1) using a modified Int system.

Main Methods:

• Engineered a variant of phage lambda integrase (Int) to target the attH4X sequence within human Long INterspersed Elements-1 (LINE-1).
• Demonstrated single-copy transgene integration into various human cell lines, including human embryonic stem cells (hESCs).
• Assessed transgene functionality, DNA damage response, and effects on endogenous gene expression post-integration.

Main Results:

• Achieved precise integration of large episomes (up to 48 kb) into the LINE-1 attH4X site in multiple human cell types.
• Confirmed stable transgene expression, including pluripotency reporters and constitutively expressed genes, in hESCs and their differentiated progeny.
• Observed no induction of DNA damage response or chromosomal aberrations, with minimal impact on global or local gene expression.

Conclusions:

• The developed Int-mediated LINE-1 targeting system enables safe and efficient single-copy integration of large multi-transgene cassettes into the human genome.
• This method overcomes limitations of existing tools, offering flexibility in clone selection based on transgene performance.
• The approach is highly promising for diverse applications in human cell engineering, biotechnology, and molecular medicine requiring stable, large-scale genetic modifications.