L1 (LINE-1) retrotransposon evolution and amplification in recent human history

Area of Science:

• Genetics
• Evolutionary Biology
• Molecular Biology

Background:

• Mammalian genomes contain abundant LINE-1 (L1) retrotransposons, comprising over 20% of DNA in some species.
• L1 elements have a long history of replication and evolution in mammals, spanning more than 100 million years.

Purpose of the Study:

• To investigate the evolutionary dynamics of the active human Ta L1 family.
• To characterize the emergence and dominance of distinct L1 subfamilies in the human genome.

Main Methods:

• Phylogenetic analysis of human L1 elements.
• Population genetics to assess insert polymorphism.
• Comparative analysis with rodent L1 families.

Main Results:

• The human Ta L1 family originated approximately 4 million years ago and diversified into Ta-0 and Ta-1 subfamilies.
• The Ta-1 subfamily is younger, now constitutes at least 50% of the Ta family, and is the replicatively dominant subfamily.
• Ta-1 inserts exhibit higher polymorphism (69%) than Ta-0 inserts (29%), with the youngest subset, Ta-1d, showing 90% polymorphism.

Conclusions:

• L1 evolution remains highly active in recent human history, comparable to rodent L1 families.
• Distinct Ta L1 subfamilies have successively emerged and amplified, demonstrating ongoing retrotransposon dynamics in humans.
• Ta-1 elements accumulate in humans at a rate similar to recently evolved active rodent L1 subfamilies.