Fwd: FW: [Food-news] Soiled Genes: Can Tocic Exposure be Inherited?

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> Editor's Note: Evidence is growing to support the

> notion that our

> environments, including the air we breathe and food

> and water we ingest,

> not only have health implications for ourselves, but

> the ways our

> environments affect our bodies can be passed on

> through generations.

> This article describes in terms accessible to lay

> people how our genes

> interact with our environments to produce health

> consequences.

>

> To participate in discussion on this or any other

> posting, please click

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<http://www.oriononline.org/pages/om/index_om.html>*ORION

>

*http://www.oriononline.org/pages/om/05-6om/Pray.html

>

> November/December 2005

>

> Leslie A. Pray

>

> *Soiled Genes: Can Toxic Exposure be Inherited?*

>

> On my wall is a framed black-and-white photograph

> from the turn of the

> nineteenth century. A young girl, my mother's

> mother, stands surrounded

> by her three older sisters and my great-grandmother,

> Margaret Hunter.

> All five look bemused, each about to crack a smile,

> as though at any

> moment they might come alive. They are taking a day

> for play away from

> their labor-intensive farm life. Margaret and

> husband Joe raised their

> four girls and five boys in the vast waving prairie

> land of Saskatchewan.

>

> These are the foods I imagine they ate: chicken and

> dumplings, pheasant

> and quail and game of all sorts, wild mushrooms,

> Saskatoon berry pie,

> and lots of bread--sugary breads, pan-fried bread

> dough, bread smothered

> with chokeberry spread.

>

> I have looked at this photo of my maternal ancestors

> many times, and I

> have wondered many things. But it only occurred to

> me recently to

> question the culinary legacy of my inheritance and

> the bounty of the

> land that nurtured my recent genetic stock. How

> might the century-old

> diet of my mother's people be affecting my health

> today? And it's not

> just the food that I wonder about. What about the

> air they breathed, the

> water they used for bathing, the materials they

> smelled and touched and

> absorbed through their skin--might any of those

> environmental exposures

> have lingering effects on my health? I ask because

> scientists have

> stumbled recently on some remarkable clues that

> suggest that we inherit

> more than our ancestors' genes. We also inherit, in

> a very real,

> physical, molecular way, their environment--not

> through our genes but

> through our epigenomes.

>

> Derived partially from the Greek prefix epi-, which

> means " on " or " in

> addition, " the epigenome is to the cell what an

> organism's sensory

> organs are to the individual. Like an octopus's

> tentacles that, among

> other functions, gather information from the

> environment so that the

> brain can tell the neurons, " Move your eighth arm

> here, " the epigenome

> gathers information from the cell's environment and

> tells the genes,

> " turn on " or " turn off. " In science lingo, it

> governs " gene expression. "

> Based on emerging evidence, the epigenome appears to

> play a vital role

> in most, if not all, cellular activity, from

> metabolism to fertilization.

>

> Imagine the genome: each of our cells has a set of

> some twenty to thirty

> thousand genes, each gene composed of hundreds to

> thousands of DNA-based

> compounds strung together like rungs on a ladder.

> The DNA compounds are

> organized into what has been famously called the

> double helix, a twisted

> ladder of molecules occupying our every cell,

> governing our body's every

> move. Now imagine this: attached like side rungs to

> the DNA ladder are

> millions of methyl molecules, each consisting of a

> single carbon and

> three hydrogen atoms. The clusters of methyl

> molecules act like sensors,

> interpreting the environment, throwing switches.

>

> Along with some other lesser-known chemical

> modifications, this

> genome-wide pattern of methyl switches is the

> epigenome, which is as

> important to the healthy functioning of a cell as

> the DNA itself. A gene

> turned on or off at the wrong time can wreak

> molecular havoc. In just

> about every kind of tumor cell ever studied, genes

> known as tumor

> suppressor genes, which normally prevent the growth

> of tumors, are

> mistakenly silenced when too many methyl molecules

> attach themselves to

> the gene. Abnormal methylation patterns have also

> been linked to such

> conditions as diabetes, obesity, autoimmune

> diseases, and psychiatric

> diseases.

>

> Although the mechanics haven't been thoroughly

> studied, it appears that

> abnormal methylation patterns result when the

> epigenome responds to

> unusual environmental signals. The epigenome is

> where our genes

> interface with the environment, reading and

> interpreting hormones,

> nutrient levels, and electrical and other signals in

> ways that enable

> the cell--and the organism--to respond appropriately

> to change and in

> ways that the genome alone cannot. Turning a gene on

> or off is a much

> faster way of adapting to an environment than

> natural selection is;

> adaptation can happen over the course of a lifetime.

> That can be a good

> thing. In 2003, scientists from Duke University

> showed that feeding mice

> unusually large amounts of nutritional supplements

> caused certain genes

> to become abnormally overmethylated, decreasing the

> animal's risk of

> cancer, diabetes, and other health problems. But it

> can also mean, as

> with turned-off tumor suppressors, that things can

> go wrong during a

> lifetime.

>

> Because the epigenome can respond so quickly to

> chemical and electrical

> changes in the cellular environment, individuals

> born with one epigenome

> will likely die with another. In a study published

> by the National

> Academy of Sciences in July 2005, researchers

> reported dramatic

> epigenomic divergence between genetically identical

> human twins, each

> twin accumulating over time its own unique set of

> methylation mutations.

> The twin study helps explain why genetically

> identical individuals who

> grow up in different environments develop different

> health problems.

>

> Researchers have known for decades that the

> epigenome exists. But for

> years, all eyes were on the genes, says Richard

> Strohman, professor

> emeritus of microbiology at University of

> California, Berkeley. " If you

> have a new idea that contrasts with or is critical

> of the main pattern

> of belief, " says Strohman, " you won't be listened

> to. " But in the last

> twenty years investigators have uncovered enough

> molecular detail to

> convince the scientific community at large that the

> epigenome matters.

> And within the last five years geneticists have

> uncovered enough

> evidence about the epigenome's environmental

> sensitivity from

> experiments like the twin study to cautiously raise

> a fundamental

> question: when it comes to human health, might the

> environment matter

> more than our genes?

>

> The question has taken on new gravity in light of

> evidence, reported in

> the June 2005 issue of /Science/ magazine, that

> epigenetic change can be

> inherited. Researchers from Washington State

> University showed that

> pregnant rats exposed to pesticides not only

> suffered epigenetic damage

> but also passed it down three generations, to the

> great-grand-offspring.

> More than 90 percent of male offspring, across all

> three generations,

> were born with infertility problems, all of which

> were due to that

> initial pesticide exposure. The study did not report

> which abnormal

> methylation pattern or other chemical modifications

> to the genome might

> have caused the inherited toxin damage, but it did

> rule out DNA mutation.

>

> The Washington State study corroborates at least two

> earlier studies,

> involving mice and fruit flies, that found that

> epigenetic change could

> be inherited. Taken together, the evidence lends

> credence to the

> controversial theory of eighteenth-century

> naturalist Jean Baptiste de

> Lamarck, who argued that organisms acquire useful

> traits during their

> lifetimes and pass them on to their offspring.

>

> I doubt, perhaps naïvely, that my

> great-grandmother's and my

> grandmother's epigenomes suffered much environmental

> harm, living as

> they did off the land, before the beginning of the

> chemical onslaught

> that we know today. But what of their London-bred

> forbears? Did the

> belching coal smoke, the soot, the stench-filled

> sewage of the Thames

> cause epigenetic change? If so, was it passed down

> and ferried through

> the germ line, across the Atlantic, to my mother's

> family and eventually

> to me?

>

> More importantly, what have I and my siblings

> consumed, touched, and

> breathed, and how will it affect our children and

> grandchildren and

> great-grandchildren? The epigenome's role as

> environmental sensor should

> give us cause to think about environmental health in

> a different way.

> Science has now provided evidence that when organic

> solvents and other

> toxic chemicals are released into the air we

> breathe, the water we

> drink, the soils that grow our food, it is our

> progeny who inherit the

> results. If nothing else, this serves as a helpful

> reminder to think

> less of ourselves, and more of our genetic

> heritage-- " our link with the

> past and future, " as Rachel Carson put it, " a

> possession infinitely more

> valuable than individual life. "

>

> *Leslie A. Pray*, a biologist and educator, writes

> policy reports for

> the Board on Global Health at the National Academy

> of Sciences. Her work

> has appeared in the /Chronicle of Higher Education/,

> /Next Wave/, /The

> Scientist/, /Wild Earth/, and other publications.

> She lives in Western

> Massachusetts.

>

> --

>

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