Thursday, August 29, 2013

Core Misconcept: Epigenetics

Sarah C.P. Williams is a science writer. She published an article in PNAS last February: Epigenetics. Here's the opening paragraphs ...
Despite the fact that every cell in a human body contains the same genetic material, not every cell looks or behaves the same. Long nerve cells stretch out the entire length of an arm or a leg; cells in the retina of the eye can sense light; immune cells patrol the body for invaders to destroy. How does each cell retain its unique properties when, in its DNA-containing nucleus, it has the same master set of genes as every other cell? The answer is in the epigenetic regulation of the genes: the control system that dictates which of many genes a cell uses and which it ignores. The same mechanism could also explain why identical twins—who have identical genes—can develop different diseases, traits, or personalities.

Epigenetic regulation consists of chemical flags, or markers, on genes that are copied along with the genes when the DNA is replicated. Without altering the sequence of DNA’s molecular building blocks, epigenetic changes can alter the way a cell interacts with DNA. These changes can block a cell’s access to a gene, turning it off for good.
Statements like that make me cringe. No only is she ignoring decades of work on the real explanation of differential gene expression, she is also proposing an explanation that can't possibly live up to the claim she is making.

PNAS should be embarrassed.

Fortunately, I'm not the only one who was upset. Mark Ptashne had the same reaction as several hundred other scientists but he took the time to write up his objections and get them published in the April issue of PNAS [Epigenetics: Core Misconcept]. I'll quote his opening paragraph and then let you follow the link and get educated about real science.
Indeed understanding this problem has been an overarching goal of research in molecular, developmental, and, increasingly, evolutionary biology. And over the past 50 years a compelling answer has emerged from studies in a wide array of organisms. Curiously, the article ignores this body of knowledge, and substitutes for it misguided musings presented as facts.
There was a time when every molecular biology student knew how gene expression was controlled. They knew about the pioneering work in bacteria and 'phage and the exquisite details that were worked out in the '60s, '70s, and '80s. That information has been lost in recent generations. Our current crop of graduate students couldn't tell you how gene expression is controlled in bacteriophage λ.

If you are one of those students then I urge you to read Ptashne's book A Genetic Switch before it goes out of print. If the current trends continue, that information is soon going to pass out of the collective memory of molecular biologists just as it has been forgotten (or never learned) by science writers.