Date: Thu, 06 Nov 97 01:18:33 EST
From: C <THCLAX00@UKCC.UKY.EDU>
Subject: INFOTERRA: Radiation
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URL:
http://www-news.ucdavis.edu/PubComm/newsreleases/11.97/news_radeffects.html
Title: Radiation Effects/UC Davis/11-4-97
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<UC Davis News> November 4, 1997
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Study Shows Hereditary Legacy of Radiation Exposure
Ever since the atomic bombs dropped on Japan created the world's largest
experiment on the effects of radiation on humans, people have puzzled over not
only just what these effects could be, but also if they could be passed on to
the children of those exposed. In the past, researchers have shown in mice
that some effects -- in the form of genetic mutations -- can indeed be passed
to offspring and cause health effects.
Now Lynn Wiley and her colleagues at the University of California, Davis, and
Lawrence Livermore National Laboratory have used a very sensitive model they
developed to demonstrate that if a male mouse is exposed to radiation, he may
pass on detrimental effects not only to his children, but also to his
grandchildren, and even great-grandchildren.
Wiley will present her work at a conference Nov. 8-9 in Japan called
"Bioregulation of Radiation Response: Genetic Instability." Most of the
information she presented was published this summer in the journals Radiation
Research and Mutation Research .
Wiley says that her "environmentally relevant" assay -- using amounts of
radiation that compares to what a person might receive during radiation
therapy for cancer -- confirms what the Japanese have been saying for years;
that the effects of radiation can be passed down through generations. Her
results are controversial but she says, "so far, no one's been able to knock
it down ... Every molecule of that paper has been turned over, and it hasn't
been shot down."
"There is a big difference between transmission, which means passing on
effects to the children, and heritability, which means passing it on to all
future generations," said Wiley, a professor of medicine with the campus
Institute of Toxicology and Environmental Health. "Heritability means that it
has survived a complete round of DNA replication, and that it is stable in the
DNA of the sperm."
The method that Wiley and her colleagues used is much more sensitive than
those used in conventional mouse studies, which use hundreds of thousands of
mice. Hers uses only about 75 mice at a time. According to Wiley, what is new
about her findings is that she saw the radiation effects in the small numbers
of mice she used, indicating that the radiation is affecting DNA
non-specifically; in other words, it's affecting many genes.
Wiley exposed eight or so male mice at a time to the radioisotope Cesium-137,
and allowed these mice to mate with females once a week for eight weeks, to
cover the sperm-making history of the father. The sons of these irradiated
fathers were allowed to mate with females beginning at eight weeks of age to
produce the grandchildren that were used in Wiley's study.
In the assay developed by Wiley more than 10 years ago, embryos consisting of
only four cells are removed from the mother. These cells are then combined
with four cells from another embryo -- one without a history of radiation --
and allowed to multiply several times. Then the scientists count the total
number of cells (one of the embryos has a special marker so it can be
distinguished from the other). If there are fewer cells from the cells that
received radiation, then they have a growth disadvantage from inherited DNA
damage, according to Wiley.
Wiley said she found a significant reduction in cell reproduction and growth
in the offspring of mice that had been irradiated six or seven weeks before
conception, corresponding to a sensitive stage in sperm development. These
grandchildren mice also weigh less than normal mice and their sperm are less
efficient at fertilization.
Wiley suspects her fairly simple, yet exquisitely sensitive, cellular assay
could be used to predict inherited effects of radiation in future generations
of animals. The reproductive toxicology professor is now continuing her
studies to look at lower doses of radiation, and to determine on a genetic
level what the changes are that are induced by radiation.
"The human side of these studies is that we already have in mice documented
irradiation effects that are passed on to future generations, ones that are
causing cell growth and reproduction changes," she said. "If you mess around
with that, you can't help but wonder if these changes will turn out to be
cancerous or impair reproduction."
Wiley's work was funded by the National Institutes of Health .
Media Contact:
--Mitzi Baker, News Service, (916/530) 752-8248, mabaker@ucdavis.edu
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