Tuesday, March 14, 2006

Convergent Evolution of Molecules in Electric Fish

Having a set of extra genes gave fish on separate continents the ability to evolve electric organs, report researchers from The University of Texas at Austin.

Dr. Harold Zakon and colleagues, in a paper recently published in Proceedings of the National Academy of Sciences, show that African and South American groups of fish independently evolved electric organs by modifying sodium channel proteins typically used in muscle contraction.

Mutations in sodium channel proteins can cause serious muscular disorders, epilepsy and heart problems in humans and other vertebrates.

But fish have two copies of many of their genes, and Zakon found that the duplicate sodium channel gene could mutate and evolve without harming the fish.

"The spare gene gave [the electric fish] a little bit of evolutionary leeway," says Zakon, professor of neurobiology. "This is really one of the first cases that the ancestral gene duplication in fish has actually been linked to a gene that has been freed up and evolving in accordance with a ‘new lifestyle.’"

Zakon and colleagues looked at two sodium channel genes in the electric organs and muscles in electric and non-electric fish. Electric fish use their electric organs, which are modified muscles, to communicate with each other and sense their environment.

The researchers found that electric fishes expressed one of the sodium channel genes in their electric organs only, while non-electric fish express both genes in their muscles.

"Most fish have both genes in the muscle, but as the new electric organ was evolving, the sodium channel—by being lost from the muscle—became devoted to the electric organ," Zakon says. "So two times, independently, the gene has been ‘lost’ from the muscle. It’s no longer able to turn on in a cell that for millions of years it turned on in, and now it’s turning on in this new organ."

When the research team looked at the sodium channel protein sequences, they found that some of the mutations occurred at the same or very close to sites in the protein where mutations have been shown to cause disease in humans.

"Functionally important parts of this molecule are changing in order to change the electrical discharge in the fish—changes that would be detrimental in a human muscle," says Zakon.
Looking at the convergent evolution of sodium channels in these fish helps neurobiologists identify important parts of these proteins relevant to human health, adds Zakon.

"When natural selection is acting to cause changes in a part of a molecule, you know it’s functionally important," he says. "Natural selection can start showing you the important parts of molecules. We took the evolutionary approach, which is very compatible with the clinical approach."The research team included evolutionary biologist Dr. David Hillis, graduate student Derrick Zwickl and research associate Ying Lu.

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AGRI-INFO/MARCH 14, 2006


TITLE: CONVERGENT EVOLUTION OF MOLECULES IN ELECTRIC FISH

ALAM BA NINYO NA ANG ELECTRIC FISH AY MAY KAKAYANAN NA MAG-UPGRADE O MAG-EVOLVE NG KANILANG ELECTRIC ORGANS SA PAMAMAGITAN NG MGA TAGLAY NILANG EXTRA SET NG GENES.

SA PANANALIKSIK NA GINAWA NG ISANG GRUPO NG RESEARCHERS SA PANGUNGUNA NI DR. HAROLD ZAKON NG UNIVERSITY OF TEXAS SA AUSTIN, NATUKLASAN NA ANG AFRICAN AT SOUTH AMERICAN GROUPS NG MGA ISDA AY KAPWA MERONG KAKAYANANG MAG-EVOLVE NG KANI-KANILANG ELECTRIC ORGANS.

ITO AY MAAARING MAGAWA NG MGA ISDANG ITO SA PAMAMAGITAN NG PAGBABAGO O MODIFICATION SA KANILANG SODIUM CHANNEL PROTEINS NA KARANIWANG GINAGAMIT SA MUSCLE CONTRACTION.

ANG ANUMANG MUTATION SA SODIUM CHANNEL PROTEINS AY MAAARING MAGING SANHI NG MATINDING MUSCULAR DISORDERS, EPILEPSY AT HEART PROBLEMS SA TAO AT IBA PANG VERTEBRATES.

NGUNIT ANG MGA ISDA AY MERONG DALAWANG KOPYA NG KARAMIHAN SA KANILANG GENES S AKATAWAN AT NATUKLASAN NG GRUPO NI ZAKON NA ANG DUPLICATE SODIUM CHANNEL GENE AY MAAAARING MAG-MUTATE AT EVOLVE NANG WALANG MASAMANG EPEKTO SA ISDA.

AYON KAY ZAKON, PROFESSOR DIN NG NEUROBIOLOGY, ANG SPARE GENE AY NAGBIBIGAY SA ELECTRIC FISH NG TINATAWAG NA EVOLUTIONARY LEEWAY. ITO AY ISA SA MGA KAUNA-UNAHANG MGA KASO KUNG SAAN ANG ANCESTRAL GENE DUPLICATION SA ISDA AY MAY AKTUWAL NA UGNAYAN SA GENE NA NAPALAYA NA AT NAG-E-EVOLVE ALINSUNOD SA BAGONG LIFESTYLE.

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