ANTISENSE NON-CODING RNAs REGULATE VAR GENES ACTIVATION IN PLASMODIM FALCIPARUM

The virulence of Plasmodium falciparum, the causative agent of the deadliest form of human malaria is attributed for its ability to evade human immunity through antigenic variation. These parasites alternate between expression of variable antigens, encoded by members of a multi-copy gene family named var. Immune evasion through antigenic variation depends on tight regulation of var gene expression ensuring that only a single var gene is expressed at a time while the rest of the family is maintained transcriptionally silent. Understanding how a single gene is being chosen for activation is critical for understanding mutually exclusive expression but remains a mystery. We showed that antisense ncRNAs initiating from var introns are associated with the single active var gene at the time in the cell cycle when the single var promoter is active. We further show that these transcripts are co-localized in the nuclear periphery and binds nuclear proteins. We demonstrate that expression of these antisense ncRNAs in trans triggers activation of a silent var gene. On the other hand, interference with these ncRNAs using complement Peptide Nucleic Acid molecules (PNAs) repressed transcription of the active var gene. Altogether our data provide evidence that these antisense ncRNAs play a key role in regulating var gene activation and mutually exclusive expression.