Science Matters: Human genome continues to surprise

[Guest guest]

Here's your weekly Science Matters column by David Suzuki.

 

Human genome continues to surprise

 

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 naiveté. 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.