The critical role of bromodomain proteins TgBDP1 and TgBDP2 in regulating gene expression in the protozoan parasite Toxoplasma gondii.

Toxoplasmosis is an incurable disease that infects at least 20% of Americans. Caused by the protozoan parasite Toxoplasma gondii, toxoplasmosis is a significant opportunistic infection in the immunocompromised when the dormant bradyzoites that are responsible for chronic disease are reactivated to the proliferative tachyzoites to cause acute disease, often leading to organ failure and death. The current treatment options are problematic due to significant side effects and allergic reactions and importantly, none kill the dormant cyst stage of the parasite. To develop more effective therapies, we must identify a unique parasite target that is essential for parasite survival.

Epigenetic regulators are necessary for the tight transcriptional control that Toxoplasma relies on to survive. The bromodomain proteins TgBDP1 and TgBDP2 play an essential role in this process, but their precise function is unknown. Importantly, they are distinct from any human bromodomains, suggesting that they may be promising candidates for developing a safe and effective drug against Toxoplasma. Toward drug development efforts for optimal treatment of toxoplasmosis, we will determine the essential role of these bromodomains during parasite infection. We have hypothesized that TgBDP1 and TgBDP2 interact with transcriptional complexes and are recruited to the promoter regions of activated genes.

We will employ state-of-the-art techniques including CRISPR genome modification, next generation sequencing and proteomics to address the key contributions of TgBDP1 and TgBDP2 to Toxoplasma gene expression and viability. We will determine the essential contribution of these bromodomain proteins to parasite gene expression by deep sequencing analysis of the parasite transcriptome during inducible BDP knockdown. Once we have identified the gene targets for TgBDP1 and 2 by chromatin immunoprecipitation and deep sequencing, we will determine how they are recruited to these specific loci, whether through their association with transcription factors or by recruitment to specific histone modifications. Identifying the function of these factors will provide significant new insight into the molecular mechanisms underlying parasite viability and infection.