Genetic elements that jump around the genome can influence brain circuitry, according to US researchers. In a study of adult rat hippocampal neural stem cells, Fred Gage and colleagues at the Salk Institute for Biological Studies in La Jolla, Calif., discovered an up to twofold enrichment of the transcripts of retrotransposons known as L1 elements.1 "This is the first evidence [that retrotransposition] events might be occurring in developing neurons seen in the adult brain," says Haig Kazazian at the University of Pennsylvania.

To investigate how L1s might retrotranspose, Gage's team used a human L1 engineered with an enhanced green fluorescent protein that activated only when the entire construct underwent retrotransposition. In mice bearing this construct, immunofluorescence microscopy revealed fluorescence only in germ cells and brain tissue.

Human L1 contains two binding sites for Sox proteins, which are expressed in brain and testis. Using RNA interference to decrease Sox2 in...

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