The interaction between the nucleosome and the DNA wrapped around it has direct effects on chromatin structure at the gene locus but also on the genome structure within the nucleus. Distinct modifications at specific histone residues have different implications for the structure of the chromatin and the extent of transcriptional output at that locus. As the full complement of histone modifications in apicomplexan parasites is identified, the dynamics of these modifications may be surveyed over the course of parasite development through stages of proliferation and dormancy and in adaptation to different hosts.

Genome sequencing and gene annotations predict that the histone sequences for the Apicomplexa are reasonably well conserved with model eukaryotes, with the exception of the histone H2B.z variant that is unique to the phylum 1, 2, 3•, 4, 5. Initial chromatin immunoprecipitation (ChIP) studies in Plasmodium falciparum and Toxoplasma gondii confirmed that conserved activating histone PTMs such as histone acetylation were abundant in active euchromatin, while repressive marks were associated with restrictive heterochromatin, consistent with their impact on the regulation of gene expression 6, 7, 8, 9. On stage-specific genes, histone marks are dynamic across parasite life cycles, confirming their key regulatory roles and that their deposition on the chromatin must be controlled 6, 7, 10, 11, 12, 13•, 14•, 15••, 16••, 17. Many of the ‘writers’ and ‘erasers’ that are responsible for the addition and removal of histone acetylation and methylation that are well characterized in model organisms are found in apicomplexans. However, the full complement of histone modifiers appears to be reduced compared with organisms from the Opisthokonta [18], hinting at novel mechanisms for regulating histone mark dynamics in species from the phylum Apicomplexa. This review focuses on the recent developments in understanding how modulation of histone modifications drives apicomplexan development. A more detailed discussion on the molecular mechanisms underlying histone modifications regulating gene expression in P. falciparum and Toxoplasma may be found 13•, 19, 20, 21••, 22, 23.