Switching trypanosome coats: what's in the wardrobe?

The African trypanosome Trypanosoma brucei is best known for its extraordinarily sophisticated antigenic variation of a protective variant surface glycoprotein (VSG) coat. T. brucei has > 1000 VSG genes and pseudogenes, of which one is transcribed at a time from one of multiple telomeric VSG expression sites. Switching the active VSG gene can involve DNA rearrangements replacing the old VSG with a new one, or alternatively transcriptional control. The astonishing revelation from the T. brucei genome sequence is that < 7% of the sequenced VSGs seem to have fully functional coding regions. This preponderance of pseudogenes in the VSG gene repertoire will necessitate a rethink of how antigenic variation in African trypanosomes operates.