Introduction: Trypanosoma brucei uses antigenic variation to evade the host antibody
clearance by periodically changing its Variant Surface Glycoprotein (VSGs) coat. T. brucei encode
over 2,500 VSG genes and pseudogenes, however they transcribe only one VSG gene at time from
one of the 20 telomeric Expression Sites (ESs). VSGs are transcribed in a monoallelic fashion by
RNA polymerase I from an extranucleolar site named ES body. VSG antigenic switching occurs by
transcriptional switching between telomeric ESs or by recombination of the VSG gene expressed.
VSG expression is developmentally regulated and its transcription is controlled by epigenetic mechanisms
and influenced by a telomere position effect.
Conclusion: Here, we discuss 1) the molecular basis underlying transcription of telomeric ESs and
VSG antigenic switching; 2) the current knowledge of VSG monoallelic expression; 3) the role of
inositol phosphate pathway in the regulation of VSG expression and switching; and 4) the developmental
regulation of Pol I transcription of procyclin and VSG genes.
Keywords: Trypanosoma, Antigenic variation, Variant surface glycoproteins, Transcriptional regulation, RNA polymerase I,
Epigenetic, Telomere position effect, Allelic exclusion.
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