Reading between the LINEs: human genomic variation induced by LINE-1 retrotransposition

Area of Science:

• Genetics
• Human Evolution
• Molecular Biology

Background:

• Mobile genetic elements, such as Long interspersed elements (LINEs), are significant components of mammalian genomes.
• LINE-1 (L1) elements comprise ~15% of the human genome, with many being truncated copies of active retrotransposition elements.
• Recent L1 insertions create polymorphic sites in the human genome, useful for evolutionary studies.

Purpose of the Study:

• To develop and characterize novel genetic markers for human evolution studies using polymorphic Long interspersed elements (L1).
• To establish polymerase chain reaction (PCR)-based assays for identifying and analyzing L1 insertion polymorphisms.
• To investigate the distribution and evolutionary history of specific L1 elements across human and nonhuman primate populations.

Main Methods:

• Development of a PCR-based display for identifying dimorphic L1 elements in the human genome.
• Creation of specific PCR assays to characterize six polymorphic L1 elements.
• Analysis of human/rodent hybrid cell lines to determine chromosomal locations of L1 elements.
• Phylogenetic analysis of nonhuman primate DNA to assess the evolutionary age of L1 insertions.
• Genotyping of diverse human populations to evaluate allele frequencies and heterozygosity.

Main Results:

• A PCR-based method was successfully developed for identifying polymorphic L1 elements.
• Six specific polymorphic L1 elements were characterized using PCR assays.
• Polymorphic L1 elements were mapped to various chromosomes in the human genome.
• Phylogenetic analysis confirmed that recently integrated L1 elements are human-specific, absent in nonhuman primates.
• Analysis of human populations revealed variable allele frequencies and heterozygosity for these L1 elements.

Conclusions:

• Polymorphic Long interspersed elements (L1) represent a novel class of genetic markers for human evolution research.
• These L1 insertion polymorphisms are stable, easily typed via PCR, and provide identity by descent information.
• The ancestral state (absence of L1) allows for rooted phylogenetic analyses of population relationships.
• L1 elements offer a valuable new source of variation for studying human population genetics and evolutionary history.