Introductory T. gondii has a complex life cycle typified by an asexual development taking place in vertebrate, and a sexual reproduction which occurs exclusively in felids and thereby is less studied. The developmental transitions rely on changes in gene expression patterns, and recent studies have assigned roles for chromatin shapers, including histone modifications, in establishing specific epigenetic programs for each given stage. Here, we identified T. gondii microrchidia (MORC) protein as an upstream transcriptional repressor of sexual commitment. MORC, in partnership with Apetala (AP2) transcription factors, was shown to recruit the histone deacetylase HDAC3, thereby impeding the chromatin accessibility of the genes predestined to be exclusively expressed in sexual stages. We found that MORC-depleted cells underwent marked transcriptional changes, resulting in the expression of a specific repertoire of genes, and revealing a shift from asexual proliferation to sexual differentiation. MORC acts as a master regulator that directs the hierarchical expression of secondary AP2 factors, with these latter potentially contributing to the unidirectionality of the life cycle. Thus, MORC plays a cardinal role in the T. gondii life cycle, and its conditional depletion offers a way to study the parasite’s sexual development i n vitro, and is proposed as an alternative to the requirement of cat infections.

CD44 is a transmembrane glycoprotein that is linked to various biological processes reliant on the epigenetic plasticity of cells, including development, inflammation, immune responses, 20 wound healing and cancer progression. While thoroughly studied, functional regulatory roles of this so-called 'cell surface marker' remain elusive. Here, we report the discovery that CD44 mediates endocytosis of iron interacting with hyaluronates in tumorigenic cell lines and primary cancer cells. We found that this glycan-mediated iron endocytosis mechanism is enhanced during epithelial-mesenchymal transition, unlike the canonical transferrin-dependent pathway. This transition is further characterized by molecular changes required for iron-catalyzed oxidative demethylation of the repressive histone mark H3K9me2 that governs the expression of mesenchymal genes. CD44 itself is transcriptionally regulated by nuclear iron, demonstrating a positive feedback loop, which is in contrast to the negative regulation of transferrin receptor by excess iron. Finally, we show that epigenetic plasticity can be altered by interfering with iron 30 homeostasis using small molecules. This comprehensive study reveals an alternative iron uptake mechanism that prevails in the mesenchymal state of mammalian cells, illuminating a central role of iron as a rate-limiting regulator of epigenetic plasticity.