A MORC-driven transcriptional switch controls Toxoplasma developmental trajectories and sexual commitment

Abstract

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.

Toxoplasma gondii AP2XII-2 Contributes to Proper Progression through S-Phase of the Cell Cycle

“…We recently reported that the essential histone acetyltransferase (HAT) GCN5b operates in a multisubunit complex with at least two ApiAP2 factors, AP2IX-7 and AP2XII-4, to activate gene expression ( 38 ). In the current study, we found that AP2IX-4 and APXII-2 interact with the recently described MORC complex, which contains transcriptional repressive proteins, including histone deacetylase HDAC3 ( 24 ). Identifying AP2IX-4 as an interactor with MORC validates our previous observation that loss of AP2IX-4 results in upregulation of a subset of bradyzoite genes ( 23 ).…”

“…2 shows a volcano plot generated with P values (−log 10 P values) and fold change values (log 2 FC) for the 136 protein hits detected from mass spectrometry. Together, the proteins complexed with AP2IX-4 overlap the recently elucidated microrchidia (MORC) repressor complex that has been implicated in silencing genes associated with the T. gondii sexual stages ( 24 ). Thus, our findings bolster the observation that multiple AP2 factors recruit MORC to regulate gene expression and provide an explanation as to why the loss of AP2IX-4 resulted in the dysregulation of genes ( 23 ).…”

“…The mRNA levels of the other proteins pulled down with AP2IX-4 represented constitutive expression. Although it showed considerably lower peptide counts, AP2VIIa-3 is another AP2 factor that purified in the AP2IX-4 interactome that was also identified in the MORC complex ( 24 ). AP2VIIa-3 is not cell cycle regulated ( Fig.…”

“…To better understand the role of AP2IX-4, we purified the AP2IX-4 complex in this study, finding that it associates with the microrchidia (MORC) transcriptional repressor complex ( 24 ). We further interrogated the function of an AP2IX-4-interacting protein, AP2XII-2, which largely shares its cell cycle expression profile.…”

Exploring the virulence gene interactome withCRISPR/dCas9 in the human malaria parasite

“…As the Pf MORC sequence diverges from that of MORC proteins found in other eukaryotes, it is unclear what transcriptional role it might play with ISWI in P. falciparum . A recent study in another apicomplexan parasite, Toxoplasma gondii , showed that MORC associates with ApiAP2 transcription factors and a histone deacetylase (HDAC3) to transcriptionally silence specific cohorts of genes important for sexual differentiation (Farhat et al , ). This MORC/HDAC3 complex seems to modulate nucleosome positioning and/or histone acetylation to directly silence transcription or act as a barrier to neighboring euchromatin.…”