Trypanosoma brucei subtelomeres: Monoallelic expression and antigenic variation

Large families of Variant Surface Glycoprotein (VSG) contingency genes are found at African trypanosome subtelomeres. These parasites offer an important evolutionary perspective on subtelomeres since they diverged very early from the eukaryotic lineage. The VSGs are also key virulence determinants. Trypanosoma brucei subtelomeres display a remarkable transcription pattern that allows VSGs to enable an extremely effective form of antigenic variation and host immune evasion. This involves monotelomeric, polycistronic transcription, driven by extranucleolar RNA polymerase I. Here, we discuss this novel epigenetic system in terms of regulatory factors and mechanisms.