UC Riverside

Toxoplasma gondii is a prolific parasite known to infect a wide variety of warm-blooded animals, including humans. The parasite can interconvert between a dormant form of the parasite (bradyzoites), and an acute form of the parasite (tachyzoites), which manifests as Toxoplasmosis, in a process called recrudescence. This process is tightly controlled through a series of changes in gene expression in response to environmental pressure. Histone modifications are effective post-translational modifications, influencing the parasite’s gene expression through different stages of its life cycle. Despite knowing that recrudescence is, in part, epigenetically regulated, little is known about how environmental factors, such as the type of host cell, affect this process. This study uses histone modifications to observe changes in the epigenomic profile of the parasite as they develop within two different host cells, Astrocytes (ASTs) and Human Foreskin Fibroblasts (HFFs). Using Chromatin Immunoprecipitation followed by deep Sequencing (ChIP–seq) against three different histone marks, we revealed a higher abundance of histone H3K4me3 activating marks within ASTs. This observation was supported by an increased binding affinity of H3K4me3 in ASTs and a decline in the number of affinity binding sites in HFF as recrudescence progressed. Of the annotated genes that were identified to have a high affinity with H3K4me3, several had potential roles in invasion, chromatin remodeling, and cell cycle progression.