DNA Dumpster Diving: A Q&A With Biologist Nelson Lau

Erin Farley

Since the 1960s, scientists have tended to believe that most of the DNA in the human genome is junk. The DNA that doesn’t encode proteins — the main activity of our genes — was assumed to serve no purpose.

But assistant biology professor Nelson Lau is among a new generation of scientists questioning that hypothesis. His findings suggest it may be time for a reappraisal of junk DNA. To understand how our bodies work, he thinks, we need to pick through our genetic garbage.

First off, what is “junk DNA”?

About 2 percent of our genome carries out functions we know about, things like building bones or keeping the heart beating. What the rest of our DNA does is still a mystery. Twenty years ago, for want of a better term, some scientists decided to call it junk DNA.

Is it really junk?

There are two camps in the scientific community, one that believes it doesn’t do anything and another that believes it’s there for a purpose.

And you’re in the second camp?

Yes. It’s true that sometimes organisms carry around excess DNA, but usually it is there for a purpose. Perhaps junk DNA has been co-opted for a deeper purpose that we have yet to fully unravel. Let’s get down to the nitty-gritty.

You study the PIWI [pronounced “pee-wee”] pathway. First, what is a pathway?

A pathway is a combination of genetic and biochemical reactions.

And the PIWI pathway, specifically?

Much of junk DNA is the remnants of viruses and other genomic parasites that have infiltrated the human genome over hundreds of millions of years of evolution. The PIWI pathway keeps them from spreading. It’s like the junk DNA are outlaws, and the PIWI pathway keeps them from escaping from jail.

What would happen if they did escape?

It would stop our germ cells, our sperm and eggs, from developing normally. The human race would cease to exist.

But wait a second. Your research has shown some bits of junk DNA don’t get stopped by the PIWI pathway.

Yes. Every once in a while, it sneaks out past the cop.

So why hasn’t our species gone kaput?

It’s not enough to do damage. In fact, it might be good for us. I like to recall the idiom “One man’s junk is another man’s treasure.”

Huh?

Maybe when junk DNA moves to the right place in our DNA, it causes better or faster evolution. Maybe when junk genes interact with the nonjunk ones, it causes a mutation to occur so humans can better adapt to changes in the environment.

Which would mean junk DNA does have a function after all.

Exactly.

So shouldn’t we stop calling it junk?

I’d like to call it the “dark matter” of the genome. Dark matter composes much of the universe, but it remains a mystery. Likewise, there’s dark matter in our genome we don’t understand yet.

One last question: Why do they call it PIWI?

When the PIWI pathway was knocked out in the fruit fly, it developed tiny testes. PIWI stands for “P-element induced wimpy testis.”

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