Chromatin modifications: implications in the regulation of gene expression in Toxoplasma gondii.

The apicomplexan Toxoplasma gondii completes its life cycle by successive processes of parasite differentiation that rely on a tight control of gene expression to ensure appropriate protein profiles on time. During the last 5 years, several groups have pioneered this field of investigation, suggesting that epigenetics could play an important role in the control of parasite gene expression. Histone modifications serve as an effective way to regulate gene transcription but they do not operate alone; rather, they act in concert with other putative epigenetic information carriers (histone variants, small RNAs) and DNA sequence-specific transcription factors to modulate the higher-order structure of the chromatin fibre and govern the on-time recruitment of the transcriptional machinery to specific genes. Regarding the 'histone code' hypothesis, the parasite is endowed with a rich repertoire of histone-modifying enzymes catalysing site-selective modifications, which are subsequently interpreted by effector proteins that recognize specific covalent marks. Still, several peculiarities seem unique to T. gondii. This review is a synthesis of the current knowledge of how epigenetics contribute to the control of gene expression in T. gondii and, likely, other Apicomplexa.