'Jumping genes' contribute to the uniqueness of individual brains ( ery time the engineered L1 element jump...)

'Jumping genes' contribute to the uniqueness of individual brains

ery time the engineered L1 element jumped, the affected cell started glowing green [WHY?]. "We were very excited when we saw green cells all over the brain in our mice," says research fellow and co-author M. Carolina N. Marchetto, "because then we knew it happened in vivo and couldn't be dismissed as a tissue culture artifact."

Transposable L1 elements, or "jumping genes" as they are often called, make up 17 percent of our genomic DNA but very little is known about them. Almost all of them are marooned at a permanent spot by mutations rendering them dysfunctional, but in humans a hundred or so are free to move via a "copy and paste" mechanism. Long dismissed as useless gibberish or "junk" DNA, the transposable L1 elements were thought to be intracellular parasites or leftovers from our distant evolutionary past.

It has been known for a long time that L1 elements are active in testis and ovaries, which explains how they potentially play a role in evolution by passing on new insertions to future generations. "But nobody has ever demonstrated mobility convincingly in cells other than germ line cells," says Gage.

Apart from their activity in testis and ovaries, jumping L1 elements are not only unique to the adult brain but appear to happen also during early stages of the development of nerve cells. The Salk team found insertions only in neuronal precursor cells that had already made their initial commitment to becoming a neuron. Other cell types found in the brain, such as oligodendrocytes and astrocytes, were unaffected.

At least in the germ line, copies of L1s appear to plug themselves more or less randomly into the genome of their host cell. "But in neuronal progenitor cells, these mobile elements seem to look for genes expressed in neurons. We think that's because when the cells start to differentiate the cells start to open up genes and expose their DNA to insertions," explains co- author Alysson R. Muotri. "What we have shown for th
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Source:Salk Institute

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( ery time the engineered L1 element jump...)'Jumping genes' contribute to the uniqueness of individual brains