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Sea Lamprey Jettisons One-Fifth of Its DNA During Development

Early in embryonic development, the sea lamprey discards 20 percent of its DNA and dramatically remodels its genome. This remarkable finding was reported by researchers at the University of Washington and the Benaroya Research Institute. This is believed to be the first recorded observation of a vertebrate extensively reorganizing its genome as a normal part of development. The sea lamprey is a primitive fish that emerged from jawless fish first appearing 500 million years ago. It is essentially a living fossil from around the time that vertebrates originated. Sea lampreys have a long juvenile life as larvae in fresh water, where they eat on their own. Their short adult lives are normally spent in the sea as blood-sucking parasites. Their round, jawless mouths stick like suction cups to other fish. Several circular rows of teeth rasp through the skin of their unlucky hosts. Their appetite is voracious. Later, as they return to streams and rivers along the northern Atlantic seaboard, sea lampreys atrophy until they are little more than vehicles for reproduction. After mating, they perish. The scientists don't know how the lamprey’s large-scale genome reorganization happens, or why. The lead author said that his favorite hypothesis, yet unproven, is that the extra genetic material might play a role in the proliferation of precursor cells for sperm and eggs, and in early embryonic development. The genetic material might then be discarded either when it is no longer needed or to prevent abnormal growth. This work was reported in the July 7 issue of PNAS. [Press release] [PNAS abstract]