Engineered LINE-1 retrotransposition in nondividing human neurons

Area of Science:

• Genomics
• Molecular Biology
• Epigenetics

Background:

• Transposable elements (TEs), particularly LINE-1 (L1), constitute a significant portion of the human genome.
• L1 activity contributes to genomic variation, with insertions primarily occurring during embryogenesis.
• Previous research indicated L1 activity impacts the somatic genome in the human brain, but its presence in other somatic tissues remained unclear.

Purpose of the Study:

• To investigate L1 retrotransposition rates in healthy human somatic stem cells (mesenchymal stem cells and hematopoietic stem cells).
• To compare L1 mobilization in these stem cells with neuronal precursor cells.
• To determine if L1 can retrotranspose in mature, non-dividing neuronal cells.

Main Methods:

• Utilized an engineered L1 retrotransposition assay.
• Analyzed L1 mobilization rates in human mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs).
• Compared L1 activity in MSCs and HSCs against neuronal precursor cells (NPCs) and mature neuronal cells.

Main Results:

• Observed significantly lower L1 expression and engineered retrotransposition rates in MSCs and HSCs compared to NPCs.
• Demonstrated for the first time efficient retrotransposition of engineered L1 elements in mature, non-dividing neuronal cells.
• Findings indicate L1 mobilization is not restricted to neuronal precursor cells.

Conclusions:

• L1 retrotransposition occurs efficiently in mature, non-dividing human brain cells.
• The degree of somatic mosaicism in the human brain may be significantly underestimated.
• L1 activity has a substantial, ongoing impact on the human brain genome.