Environment Becomes Heredity
Advances in the field of epigenetics show that environmental contaminants can turn genes “on” and “off,” triggering serious diseases that are handed down through generations. But there’s also a more heartening prospect: The same diseases may be treated by relatively simple changes in nourishment and lifestyle.
Let's say, just for the fun of it, that rats engage in speed dating, and we have a hidden camera. Rat A — let’s call her Betsy — is ready and willing to select a mate from a pool of males who are milling around in a separate room, downing too many cocktails. One by one, the male rats visit Betsy as she sits, nervous and inquisitive, at a little round table, toying with her bar napkin.
Rats routinely identify each other and maintain relationships via a lot of sniffing, nosing and general snorfling, and when they’re in the mood for love, they do it even more. Alas, all the snorfling in the world will not reveal Betsy’s Mr. Right tonight. Many of the potential mates who come her way just seem wrong somehow, and Betsy rejects them.
Is Betsy merely an overly picky girl destined for spinsterhood? No. Betsy is just observant — observant enough to preserve her species. You see, Betsy is a Sprague Dawley rat, a variety commonly used in biological experiments and the very kind used by Andrea Gore and David Crews of the University of Texas, Austin and Michael Skinner of Washington State University, Pullman, who have found something amazing and scary in a mate-selection experiment very similar to Betsy’s speed-dating scenario.
In the experiment, female Sprague Dawley rats were exposed to potential male suitors, some of which were descended from one great-great-grandmother rat who had been given a high dose of the fungicide vinclozolin when she was pregnant. Vinclozolin, used worldwide on a variety of agricultural products including wine grapes, is banned in Scandinavian countries, but the EPA continues to allow its use in the United States on certain crops.
Earlier experiments showed that male offspring of mothers exposed to vinclozolin were very likely to be sterile or produce sperm with impaired mobility and to develop prostate cancer, kidney disease and immune system problems as adults. Amazingly, normal females like Betsy were able to divine, probably by detecting and interpreting pheromones secreted by the males, which would-be suitors descended from that matriarch. The females spurned each and every one of them.
The “speed-dating” study — “Transgenerational Epigenetic Imprints on Mate Preference,” published in the Proceedings of the National Academy of Sciences in April 2007 — showed that the diseases persisted in the male rats for four generations. (The rats were bred young, before the diseases and the males’ reproductive problems manifested themselves.) Yet the susceptibility to disease was not because the rats’ genes had been damaged by the fungicide. Rather, it was an epigenetic phenomenon. That is, the fungicide had apparently affected the complex chemical processes required to package and activate or deactivate genes.
The studies by Gore, Crews, Skinner and their colleagues sit at the intersection of several major developments in biology. The vinclozolin acted as an endocrine disrupter, affecting male reproductive fitness. The diseases lying in wait for the adult male rats were a manifestation of the Barker hypothesis, which posits that events in very early development can result in strong susceptibility to adult disease. And the inherited disease susceptibilities are governed by the rules of epigenetics.
These paradigms were glimpsed years ago but blossomed in the last couple of decades, when high-throughput lab techniques to analyze genes and proteins became widely available. This scientific convergence is pushing seismic ripples throughout biology by remodeling long-standing assumptions about genetics. For a century after Gregor Mendel’s death, inheritable traits were thought to be determined by genes, the DNA elements in the nucleus of a cell, which could be affected by the environment only in limited ways.
Epigenetics, however, focuses on the chemical scaffolding that supports and packages DNA and activates or turns it off partially or completely. Because this scaffolding is susceptible to environmental influences, researchers now see it as central to both frightening and hopeful prospects for human health: It may be the avenue for a fearsome array of serious conditions — from cancer to obesity — that may be caused by exposure to only minuscule amounts of chemicals and that may be passed to offspring. At the same time, epigenetics holds out promise for preventing and treating those very diseases with relatively simple changes in nourishment and lifestyle.
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http://www.miller-mccune.com/article/489Mercury common cause of depression: www.flcv.com/depress.html
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