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Growth-gene mickey makes mice mini.

Growth-gene mickey makes mice mini

Gene-splicing scientists trying to make supermice even larger got mini-mice instead -- only half the size of normal and one-fourth as big as the "giants" raised in earlier experiments.

"We're ecstatic," says molecular biologist John J. Kopchick of Ohio University in Athens. His delight stems from the surprise discovery of a growth hormone look-alike that instead suppresses growth. By modifying a growth hormone gene and slipping it into mouse DNA, he and colleague Wen Y. Chen may have chanced upon a powerful tool for probing the hormone's function.

Eventually, Kopchick says, their finding might also lead to drug treatments for rare diseases of unchecked growth such as "giantism," which results when a pituitary tumor releases excess growth hormone.

Growth hormone does more than promote growth. Other functions include assisting in metabolism and stimulating the production of red blood cells and milk. The means by which the hormone carries out all of these tasks remain largely unknown.

Kopchick and Chen started with the gene that codes for bovine growth hormone and altered a sequence of its DNA that they hoped would affect growth regulation. Then they spliced this gene into the DNA of fertilized mouse eggs and observed three generations of offspring. The mutant bovine hormone apparently binds to cell receptors favored by the normal mouse hormone, but unlike the normal hormone, it doesn't turn on growth, they report in the July PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Bol. 87, No. 13).

Their discovery opens the door for further attempts to manipulate specific parts of the hormone while leaving the binding sites intact. Indeed, the Ohio scientists have already begun changing every amino acid in the molecule's apparently active region to explore the effects on its biological function, Kopchick told SCIENCE NEWS.

A growth-hormone-like substance that binds without stimulating growth "would be very useful," says molecular endocrinologist Pierre De Meyts of the City of Hope National Medical Center in Duarte, Calif. Such a tool might help researchers determine which cell receptors respond to the hormone. It might also enable them to resolve a controversy about whether growth hormone, which stimulates cells to release growth-causing agents, also acts directly to spur growth, De Meyts says.

Although the new findings "need more work" to confirm that the altered hormone blocks the normal hormone from receptors, Kopchick and Chen have made "a very important first step," De Meyts says.
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Title Annotation:growth hormone genes
Author:Weiss, Peter L.
Publication:Science News
Date:Jul 14, 1990
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