Retrotransposons Remodel the Genome

A new study reveals that retrotransposons, DNA sequences that are easily and naturally copied from one location in the genome and inserted elsewhere, particularly in developing eggs and sperm, cause dramatic rearrangements when they move from chromosome to chromosome. The study appeared in the August 9, 2002, issue of Cell.

"Textbooks always show these elements inserting themselves cleanly into new places in the DNA,” said Dr. Jef Boeke, head of the research team from Johns Hopkins University (Baltimore, MD, USA), "but we saw that about 10% of the time, in addition to inserting, they are taking out a big chunk of the chromosome.”

A total of 44 man-made insertions by the so-called "jumping genes” in two types of human cancer cells were followed as they moved within the genome. The act of insertion caused sections of existing DNA to be cut out and, in one location, caused neighboring DNA to be inverted, as though it had been removed and re-inserted backwards.

"Assuming that what we see in the laboratory is also happening in real life, it suggests that these elements have been remodeling host genomes more than previously realized, with deletions, insertions and inversions,” said Dr. Boeke. "These changes were probably frequently disastrous, but occasionally they might have benignly increased genetic variation or even improved survivability or adaptability. Such remodeling probably happened thousands of times during human evolution.”





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