Thursday, November 06, 2008

Junk DNA and Transposon Driven Evolution

A press release out of the Genome Institute of Singapore is claiming a function for junk DNA. The researchers show that a number of transcription factors bind repeats found in transposable elements.
More than 50 percent of human DNA has been referred to as "junk" because it consists of copies of nearly identical sequences. A major source of these repeats is internal viruses that have inserted themselves throughout the genome at various times during mammalian evolution. [...] The researchers showed that from 18 to 33% of the binding sites of five key transcription factors with important roles in cancer and stem cell biology are embedded in distinctive repeat families.
Now I could be wrong, but I thought we already knew that portions of these transposable elements acted as transcription factor binding sites (for example see here) so I don't think Larry over at Sandwalk is going to have to revise his estimates of junk DNA percentage yet. But what about the "deflated ego problem"? Is this an answer to Larry's excuse #5: that humans are more complex than other organisms in spite of similar gene numbers because of more complex regulatory mechanisms? Unfortunately I don't have access to the paper, but the press release and abstract seem to think so.
Over evolutionary time, these repeats were dispersed within different species, creating new regulatory sites throughout these genomes. Thus, the set of genes controlled by these transcription factors is likely to significantly differ from species to species and may be a major driver for evolution.
The argument here isn't for more complex gene regulation in humans, but rather different regulation depending on where these elements landed in early evolutionary history.


rob said...

I gotta say that I think Larry's position on 'junk DNA' is motivated by the idea that 'junk DNA' strongly argues against an intelligent designer. Within that sort of context it lowers the discussion about non-coding DNA to a level that I find uninteresting. Although his analysis of junk DNA in the post you link to is awesome, the tone sounds arrogant.
It seems insane to say, 'it's all junk because we know where it is from and can explain it's presence.' Doesn't mean it's not affecting biology at all. Merely having to replicate all that extra DNA might affect how fast cells proliferate, for example.
good post.