LINE-1 retrotransposons: mediators of somatic variation in neuronal genomes?

LINE-1 (L1) elements are retrotransposons that insert extra copies of themselves throughout the genome using a 'copy and paste' mechanism. L1s comprise nearly approximately 20% of the human genome and are able to influence chromosome integrity and gene expression upon reinsertion. Recent studies show that L1 elements are active and 'jumping' during neuronal differentiation. New somatic L1 insertions could generate 'genomic plasticity' in neurons by causing variation in genomic DNA sequences and by altering the transcriptome of individual cells. Thus, L1-induced variation could affect neuronal plasticity and behavior. We discuss potential consequences of L1-induced neuronal diversity and propose that a mechanism for generating diversity in the brain could broaden the spectrum of behavioral phenotypes that can originate from any single genome.