What determines the hierarchy of VSG antigen switching in T. brucei?

Pathogens use antigenic variation to evade host antibodies and cause diseases in humans.

Interestingly, in many species antigen switching occurs non-randomly in a hierarchical manner, with specific antigen genes selected in succession.

Trypanosoma brucei is a key model organism for the study of antigenic variation in which antigen switching hierarchies of its Variant Surface Glycoprotein (VSG) genes operate. However, how exactly this hierarchy is determined is unknown.

Studies in T. brucei have indicated that the spatial positioning of VSG genes within the nucleus is important for controlling their activation.

However, to date no systematic investigation of VSG gene nuclear positioning and antigen switching hierarchies has been performed.

In this project, I would test the hypothesis that antigen switching hierarchies in trypanosomes are mediated by the spatial positioning of VSG genes in the nucleus.

Using T. brucei cell lines in which different antigen switching pathways can be induced, I will determine whether silent VSGs in close spatial proximity to the active VSG before switch induction are selected next in the antigen switching pathway.

This will be investigated by integrating a combination of Micro-C to monitor VSG nuclear positioning before and after switching followed by scRNA-seq.

I will also develop a dCas9 artificial tethering system to tether silent VSGs either towards or away from the active VSG before switch induction to create a synthetic VSG switching hierarchy.

These experiments will generate important insights into the mechanisms which control antigen switching and provide valuable tools for studying nuclear organisation in kinetoplastid parasites.