Giardia Gene Shuffling Masks Bug from Immunity

14 December 2008


A common gut bug has evolved an ingenious strategy to outwit the immune system, helping to conceal the parasite from immune attack.

Scanning electron micrograph (SEM) of Giardia lamblia protozoan parasiteWriting in this week's Nature an Argentinian research team led by Hugo Lujan at the Catholic University at Cardoba found that Giardia lamblia, a major cause of intestinal infections worldwide, has a repertoire of 190 different coat proteins with which it can disguise itself.  The organism selects a different coat every few generations, returning the previous outfit to the genomic wardrobe to wear again in the future. 

By studying which genes were being turned on in Giardia the researchers found that the parasite uses a mechanism called RNA interference to suppress the action of the other 189 coat genes it's not using.  The bug makes short sequences of the DNA-relative RNA, which are the genetic mirror-image of the un-used coat genes.  These mirror-image RNAs lock on to their respective coat genes and prevent them from being expressed, keeping them in the closet.

Exactly how the outfit subsequently gets reshuffled to select a different coat remains a mystery, but the team suspect that chemical tags applied to the DNA, called epigenetic markers, could be responsible.  Either way, understanding this system will inevitably lead to new ways to combat the bug, which spreads via contaminated water and infects millions of people, worldwide, each year.


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