The role of an unusual variant nucleosome in Toxoplasma gondii life cycle

Program Director/Principal Investigator (Last, First, Middle): Sergio Oscar Angel ABSTRACT The parasite Toxoplasma gondii has infected up to one-third of the world’s population and can cause spontaneous abortion, birth defects, neurologic disorders, and ocular complications. T. gondii infects diverse host cells and must adapt to various environmental changes and stress conditions to complete its life cycle. Stress induces differentiation of T. gondii from tachyzoites to bradyzoites, which is facilitated by epigenetic changes in gene expression. Notably, changes in the availability of the metabolite acetyl-CoA impact cellular transcriptomes, likely through the subsequent alteration in acetylation of histones. T. gondii possesses the conserved canonical histones as well as variants of H3 and H2A families; intriguingly, the parasite also uses a unique variant called H2B.Z. This novel H2B.Z variant in T. gondii and it´s nucleosome partner H2A.Z, conform a double-variant nucleosome (DVN), located in promoters of active genes as well as bodies of genes that are not active in the tachyzoite. Both histones, which contain multiple acetylatable lysine residues, are understudied and require further investigation. Our previous results show that N-terminal tail acetylation of H2B.Z is relevant for chromatin modulation, apparently through the regulation of a positive charge patch generated when the histone is unacetylated. Considering the long N-terminal tail of H2A.Z, with 10 acetylatable lysines, it is likely that the DVN plays a role as a whole regulating this positive charge patch to modulate chromatin. This would imply a novel epigenetic mechanism. Understanding the role of this unusual DVN in T. gondii´s gene regulation promise to provide valuable insights into the parasite's adaptive strategies and may be potential targets for therapeutic intervention. Our hypothesis is that H2A.Z/H2B.Z DVN acetylation acts as a novel sensor for metabolic changes in acetyl-CoA, which epigenetically reprograms the transcriptome to use alternative energy sources and/or form bradyzoites. In Specific Aim 1, we will analyze the role of N-terminal acetylation in the DVN by generating T. gondii bearing mutations in H2A.Z, H2B.Z, or both. This work will provide innovative tools for studying how the DVN regulates parasite gene expression under various conditions, including those that drive bradyzoite differentiation. Specific Aim 2 will identify mechanisms by which the DVN is regulated and positioned by acetylation; we will identify the lysine acetyltransferase(s) responsible for DVN acetylation and DVN-interacting proteins that converts this signal into changes in gene expression. To address the mechanisms used by T. gondii to adapt to various conditions within host cells, Specific Aim 3 will determine the impact of metabolic changes on H2A.Z and H2B.Z N-terminal acetylation. Investigating how the DVN serves as an epigenetic sensor for metabolic changes and facilitates the parasite's adaptive response will fill crucial knowledge gaps in T. gondii biology, particularly regarding its adaptation within host cells. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page