Human genome continues to surprise

Science Matters by David Suzuki
Imagine discovering that the person running your favourite Fortune 500 company was not the CEO, as everyone presumed, but rather the bicycle-courier guy in spandex shorts and a goatee who everyone thought just delivered the messages.
That’s pretty much how scientists working on the ENCODE project must have felt after analyzing the first part of the human genome.
ENCODE, short for Encyclopedia of DNA Elements, is a massive project that aims to catalogue all of the functional elements of the human genome. The recently completed first stage of ENCODE catalogued just one per cent of our genetic code, but that represents some 30 million bases, or “letters” of DNA, in this case chosen randomly from 44 different parts of the genome. Analyzing that one per cent of our genetic structure took 308 scientists from 10 countries four years to complete.

All that effort has uncovered something marvelous: What I and other geneticists for decades took for granted may have been wrong. Or at least a wild simplification of what’s actually going on.
Until very recently, accepted dogma in genetics was that DNA, specifically DNA in the form of genes, contained all the instructions necessary to make proteins. These proteins then made things happen at a cellular level, thus a gene is “expressed,” and its instructions carried out. Another chemical, called RNA, was like a Xerox copy that simply replicated information from the DNA and transferred it to the area where proteins are made, shuttling information back and forth like a courier. It’s a nice, tidy explanation for a complicated process. And in hindsight, it’s probably a little too tidy.
Scientists first came up against the limits of this explanation when they mapped the human genome. To their surprise they found that people only have some 21,000 protein-encoding genes. Yet organisms like C. elegans, a tiny worm, or my specialty, the fruit fly, have almost as many – some 20,000 of them. If these genes are providing all the instructions on how to build and maintain an organism, how can such obviously more complicated creatures like humans have similar numbers of genes as simpler creatures like insects?
One answer may be found in the majority of our DNA that does not, as far as we know, code for proteins – what scientists used to call “junk.” When ENCODE researchers started their project, they probably assumed that, because only a small fraction of our DNA coded for proteins, only a small fraction of whatever they looked at would be transcribed into RNA, the messenger that delivered the instructions on how to make the protein.
Instead, ENCODE researchers found that much of the human genome is transcribing into RNA. It’s just that the information contained in it isn’t necessarily read to make proteins. So then what is the role of junk DNA and what does all this extra RNA do? As yet, no one really knows, but it’s clear that the human genome is much more than the sum of its genes. In fact, genes themselves may actually take a back seat in the development and functioning of an organism compared to RNA.
It’s amazing for me to look at what we know now compared to when I ran a genetics lab back in the 1970s. In fact, when I tell students what we used to think back then, they can’t help but giggle at our naivet?. I may be overstating the role of the bicycle courier in my Fortune 500 company analogy. But I may be understating it too. It’s still too early to say if RNA – our genetic bicycle courier – is actually running the show or not. But what has become clear is that there are a lot more bicycle couriers running around out there, delivering much more information than seems necessary and perhaps even making decisions on the fly. They may not be necessarily running the company, but they certainly have the ear of whoever does and they aren’t keeping their opinions to themselves.