Yesterday we told you about ENCODE, the recently concluded mega-project that created a kind of Encyclopedia Britannica of human gene function. Among the initiative's many findings was that so-called "junk DNA" — outlier DNA sequences that do not encode for protein sequences — are not junk at all, and are in fact responsible for such things as gene regulation, disease onset, and even human height.
And this finding also shows that scientists need to be very careful about designating something as being useless just because they don't truly understand what it does.
Junk DNA, also known as noncoding DNA, has been the dark matter of biology — a convenient placeholder for something we haven't really figured out yet. And it really shouldn't come as a complete surprise that junk DNA does in fact serve specific functions; nature tends to be rather parsimonious when it comes to these things, and isn't inclined to waste precious resources. The suggestion that 98% of our genome was essentially useless was clearly a theory that was just waiting to be overthrown.
Right, with that out of the way, here's what you need to know about the finding.
Back in 2000 at the completion of the Human Genome Project, biologists unveiled over 21,000 genes, of which only 2% were identified as being protein generators (the building blocks that make up our cells).
But what the ENCODE scientists have now discovered is that over 10,000 non-coding genes are controlling what happens to our protein-building genes. In fact, they're making a kind of single-stranded RNA that appears to help regulate gene activity. And this means that vast majority of our DNA is not making proteins to build cells — instead, it's controlling how genes work.
As a consequence, scientists now likely need to come up with a better term than "non-coding genes"; this discovery throws into question our sense of how we even define a gene — which now appears to be a collection of RNA molecules rather than a particular location on DNA.
Looking more deeply into the project's findings, the biologists (over 500 of them!) discovered that nearly 18% of our DNA is involved in regulating the DNA that codes for proteins, and that there are over four million "switches" (sites where proteins bind to DNA) that help to regulate DNA expression — of which 80% have now been identified as having a specific biochemical function. In other words, not junk.
These regulator genes serve as control mechanisms, or switches, for the DNA. They can determine which genes turn on and off, or they can act as a kind of volume knob, turning a gene up or down depending on its specific function or epigenetic response (such as DNA methylation). These differences determine whether a gene sequence produces a strand of hair, or parts of a lung — or whether someone is susceptible to high blood pressure or cardiovascular disease.
Looking ahead, the finding will help scientists better understand how genes operate in our bodies, and how they're capable of constructing macroscale organs such as livers and kidneys. Additionally, it will help biologists understand what exactly goes wrong when certain diseases strike.
You can read more about the ENCODE project at their official website.