Читать книгу Lifespan Development - Tara L. Kuther - Страница 142

These two mice are genetically identical. Both carry the agouti gene but in the yellow mouse the agouti gene is turned on all the time. In the brown mouse it is turned off.

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One of the earliest examples of epigenetics is the case of agouti mice, which carry the agouti gene. Mice that carry the agouti gene have yellow fur, are extremely obese, are shaped much like a pincushion, and are prone to diabetes and cancer. When agouti mice breed, most of the offspring are identical to the parents—yellow, obese, and susceptible to life-shortening disease. However, a groundbreaking study showed that yellow agouti mice can produce offspring that look very different (Waterland & Jirtle, 2003). The mice in the photo above both carry the agouti gene, yet they look very different; the brown mouse is slender, is lean, and has a low risk of developing diabetes and cancer, living well into old age.

Why are these mice so different? Epigenetics. The epigenome carries the instructions that determine what each cell in your body will become, whether heart cell, muscle cell, or brain cell, for example. Those instructions are carried out by turning genes on and off.

In the case of the yellow and brown mice, the phenotype of the brown mice has been altered, but the DNA remains the same. Both carry the agouti gene, but in the yellow mouse, the agouti gene is turned on all the time. In the brown mouse, it is turned off. In 2003, Waterland and Jertle discovered that the agouti female’s diet can determine her offspring’s phenotype. In this study, female mice were fed foods containing chemicals that attach to a gene and turn it off. These chemical clusters are found in many foods such as onions, garlic, beets, soy, and the nutrients in prenatal vitamins. Yellow agouti mothers fed extra nutrients passed along the agouti gene to their offspring, but it was turned off. The mice looked radically different from them (brown) and were healthier (lean, not susceptible to disease) even though they carried the same genes.

Another example supports the finding that the prenatal environment can alter the epigenome and influence the lifelong characteristics of offspring. Pregnant mice were exposed to a chemical (bisphenol-A or BPA, found in certain plastics). When female mice were fed BPA 2 weeks prior to conception, the number of offspring with the yellow obese coat color signaling an activated agouti gene increased (Dolinoy, 2008). When the pregnant mice were exposed to BPA plus nutritional supplementation (folic acid and an ingredient found in soy products), the offspring tended to be slender and have brown coats, signaling that the agouti gene was turned off. These findings suggest that the prenatal environment can influence the epigenome and thereby influence how genes are expressed—and that nutrition has the potential to buffer harm.

The most surprising finding emerging from studies of epigenetics, however, is that the epigenome can be influenced by the environment before birth and can be passed by males and females from one generation to the next without changing the DNA itself (Soubry, Hoyo, Jirtle, & Murphy, 2014; Szyf, 2015). This means that what you eat and do today could affect the epigenom—the development, characteristics, and health—of your children, grandchildren, and great-grandchildren (Bale, 2015; Vanhees, Vonhögen, van Schooten, & Godschalk, 2014).