Poster Presentation First Malaria World Congress 2018

Investigating how acetylation of histone variant PfH2A.Z and PfH2B.Z affects their chromatin localisation in Sir2A knockout parasites (#229)

Mohd Suffian Azizan 1 , Shamista Selvarajah 1 , Michaela Petter 2 , Michael Duffy 1
  1. University of Melbourne, Parkville, Victoria, Australia
  2. Universitätsklinikum Erlangen, Erlangen, Germany

A major contributor to Plasmodium falciparum virulence is the variant surface antigen called PfEMP1 (P. falciparum erythrocyte membrane surface protein 1). PfEMP1s are encoded by a large family of var genes. The switching between expression of different var genes mediates the parasite's evasion of host immunity. Var switching is achieved through several epigenetic mechanisms, including the dynamic exchange of canonical histones with histone variants to impart functionally-specialised chromatin domains. Our previous findings have shown that the histone variant PfH2A.Z is specifically enriched in nucleosomes near transcriptional start sites (TSSs) of most genes regardless of their transcriptional activity. The notable exception is the depletion of H2A.Z from the TSS of silent and transiently repressed var genes. However, we also previously found that PfH2A.Z persists at the TSSs of transiently repressed var genes in parasites lacking the Sir2A histone deacetylase; Sir2A mediates epigenetic gene silencing in facultative heterochromatin in subtelomeric regions. This points towards a potential antagonistic interaction between PfH2A.Z and the PfSir2A histone deacetylase in var gene activation and silencing. Using crosslinked-chromatin immunoprecipitation (X-ChIP) and next-generation sequencing, we immunoprecipitated chromatin from Sir2A knockout parasites with non-acetylated and acetylated PfH2A.Z alongside several other control antibodies. We found that acetylated variant histones were enriched at expressed genes and that the level of enrichment was not generally increased in Sir2A knockout parasites. However, at heterochromatin boundaries unmodified and acetylated H2A.Z extended further into heterochromatin in Sir2A knockout parasites, suggesting Sir2A provides a localised barrier to the spread of euchromatin. This preliminary study attempts to further elucidate the mechanisms employed by P. falciparum to regulate variegated, virulence gene expression, a process that is critical for pathogenesis.