The Science of Epigenetics

30 Years ago, a friend made a behavioural claim that shocked me and was considered scientific heresy. His claim was impossible, according to my genetic worldview – after all, genetics are fixed!

It turns out he was correct.

Discoveries in epigenetics are rewriting the rules of disease, heredity, and identity. With no more than a change in diet, laboratory agouti mice were prompted to give birth to young that differed distinctly in appearance and disease susceptibility. 

In 1999, biologist Emma Whitelaw, now at the Queensland Institute of Medical Research in Australia, demonstrated that epigenetic markers could be passed from one generation of mammals to the next. (The phenomenon had already been demonstrated in plants and yeast.) Like Jirtle and Waterland in 2003, Emma Whitelaw focused on the agouti gene in mice, but the implications of her experiment span the animal kingdom. It changes the way we think about information transfer across generations and her experiment demonstrates that it’s more than just DNA we inherit.

Back in 2000, Randy Jirtle, a professor of radiation oncology at Duke University, and his postdoctoral student Robert Waterland designed a ground-breaking genetic experiment. They started with pairs of fat yellow mice known to scientists as agouti mice, so-called because they carry a gene – the agouti gene – that in addition to making the rodents voracious and yellow renders them prone to cancer and diabetes. 

Jirtle and Waterland set about to see if they could change the unfortunate genetic heritage of the mice. Typically, when agouti mice breed, most of the offspring are identical to the parents: as yellow, plump and susceptible to life-shortening disease. 

The parent mice in Jirtle and Waterland’s experiment, however, produced many offspring that looked altogether different. These young mice were slender and mousy brown. Moreover, they did not display their parents’ susceptibility to cancer and diabetes and lived to an active old age. The effects of the agouti gene had been practically erased.

Remarkably, the researchers effected this transformation without altering a single letter of the mouse’s DNA. Their approach instead was radically straightforward – they changed the mother’s food. 

Starting before conception, Jirtle and Waterland fed a test group of mother mice a diet rich in methyl donors, small chemical clusters that can attach to a gene and turn it off. 

These molecules are common in the habitat and are observed in many foods, including onions, garlic, beets, and in the food and supplements often given to pregnant women. 

After being fed these foods, the methyl donors worked their way into the developing embryos’ chromosomes and onto the critical agouti gene. The mothers passed along the agouti gene to their offspring intact, but thanks to their methyl-rich pregnancy diet, they had added to the gene a chemical switch that dimmed the gene’s harmful effects.

DNA is now widely regarded as the instruction book for a body. But genes themselves need instructions for what to do, and where and when to do it. A liver cell contains the same DNA as a brain cell, yet somehow it knows to code only those proteins needed for the functioning of the liver. Those instructions are found not in the letters of the DNA itself but on it, in an array of chemical markers and switches, known collectively as the epigenome, that lie along the length of the double helix. These epigenetic switches and markers in turn help switch on or off the expression of particular genes. Think of the epigenome as complex software code, capable of inducing the DNA hardware to manufacture an impressive variety of proteins, cell types, and individuals.

The even greater surprise is the recent discovery that epigenetic signals from the environment can be passed on from one generation to the next, sometimes for several generations, without changing a single gene sequence an exciting yet frightening possibility for all breeders. 

It’s well established, of course, that environmental effects like radiation, which alter the genetic sequences in a sex cell’s DNA, can leave a mark on subsequent generations. Likewise, it’s known that the environment in a mother’s womb can alter the development of a foetus. What’s eye-opening is a growing body of evidence suggesting that the epigenetic changes wrought by one’s diet, behaviour, or surroundings can work their way into the genome and echo far into the future. 

Put simply, what you feed your dog’s particularly the mother today could affect the health and behaviour of her progeny and subsequent progeny. In recent years, epigenetic researchers have made great strides in understanding the many molecular sequences and patterns that determine which genes can be turned on and off. 

Their work has made it increasingly clear that for all the widespread attention devoted to genome-sequencing projects, the epigenome, is as critical as DNA to the healthy development of organisms, humans included. Jirtle and Waterland’s experiment was a benchmark demonstration that the epigenome is sensitive to cues from the environment. More and more, researchers are finding that an extra bit of a vitamin, a brief exposure to a toxin, even an added dose of mothering can tweak the epigenome—and thereby alter the software of our dog’s genes—in ways that affect any dogs body and brain for life.

All these discoveries are shaking the modern biological and social certainties about genetics and identity. We commonly accept the notion that through DNA, our dogs are destined to have body shapes, personalities, and diseases. Epigenetics is proving that we, as breeders and trainers, have some responsibility for the integrity of our dog’s genome. It seems that everything we do; can affect their gene expression and that of future generations. Epigenetics introduces the concept of free will for humans or a deliberate change in response to the environment we control for our dogs. 

Considering the potential epigenetic influence, as breeders, we need to critically examine everything we do with our dogs due to the possible influence that exists for the subsequent progeny. Now the question begs to ask, can epigenetic changes affect behaviour?

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