Project description:Cell cycle-dependent, intercellular transmission of Toxoplasma gondii is accompanied by marked changes in parasite gene expression.
Project description:Cyst formation is a key feature of the T. gondii life cycle but the genetic networks that drive this process are not yet fully characterized. To identify new components of this network, we compared T. gondii to its nearest extant relative Hammondia hammondi given the critical differences between these species in the timing and efficiency of cyst formation. Using transcriptional data from critical developmental and pH exposure time points from both species, we identified the gene TGVEG_311100, which we named Regulator of Cystogenesis 1 (ROCY1), as being both necessary and sufficient for cyst formation in T. gondii. Compared to WT parasites, TGVEG?ROCY1 parasites formed significantly fewer tissue cysts in response to alkaline pH stress in vitro and cysts were nearly undetectable in mouse brains for up to 9 weeks post-infection. Overexpression of tagged ROCY1 in WT parasites was sufficient to induce cyst formation in vitro in both WT and ROCY1-deficient parasites, demonstrating that ROCY1 is both necessary and sufficient for cyst formation. Moreover this induction of cyst formation required at least 1 of 3 predicted CCCH Zinc finger domains. Mice chronically infected with ?ROCY1 parasites had detectable tachyzoites in the brain for up to 37 days post-infection (while mice infected with WT parasites did not), and CNS transcriptional analyses at day 30 post-infection throughout the chronic phase of infection revealed inflammatory signatures consistent with acute infection in ?ROCY1 parasites compared to WT. Despite our inability to detect brain cysts in infected mice, both WT and ?ROCY1 knockout parasites reactivated after dexamethasone treatment with similar timing and magnitude for up to 5 months post infection, challenging the paradigm that long term parasite persistence in the CNS requires cyst formation. These data identify a new regulator of cyst formation in T. gondii that is both necessary and sufficient for cyst formation, and whose function relies on its conserved nucleic acid binding motif.
Project description:The apicomplexan parasite Toxoplasma gondii can infect humans and almost all warm-blooded animals worldwide, poses significant threat to the public health and of veterinary importance. The acute infection was characterized by fast replication of tachyzoites inside the host cells. During this fast amplification process, the gene expression is highly regulated by series of regulator networks. The G1 phase is usually conserved across species and responsible for the preparation of materials for the next replication cell cycle, but seldom regulators were identified in this stage. Here, we functionally characterized the C/G1 phase expressed ApiAP2 transcription factor TgAP2XII-8 in T. gondii tachyzoite. Conditionally knockdown of TgAP2XII-8 leads to significant growth defects and asexual division disorder. Additionally, the parasite cell cycle progression was also disrupted after TgAP2XII-8 depletion, which is characterized by G1 phase arrest. RNA-seq and CUT&Tag experiments revealed that TgAP2XII-8 played as an activator for the ribosomal proteins expressed in G1 phase. Moreover, TgAP2XII-8 bind to a specific DNA motif ([T/C]GCATGCA), which is abundant and conserved in the intergenic region of several other apicomplexans, which may suggest a broad and conserved role for this ApiAP2 in the Phylum of Apicomplexa. These data provide important knowledge for the understanding of transcriptional regulation of parasite cell cycle in T. gondii.
Project description:Toxoplasma gondii cell cycle mutant 11-104A4 reversibly arrests in the G1 phase. The defect in this mutant was mapped by genetic complementation to a gene encoding a novel AAA-ATPase/CDC48 family member (TgNoAP1). A change in a tyrosine to a cysteine upstream of an AAA+ domain leads to protein instability and results in cell cycle arrest. This factor is cell cycle regulated and exclusively expressed in the nucleolus during the G1/S phases. At high temperature the mutant quickly arrests with a single nucleus and expresses transcripts enriched in the G1 subtranscriptome. This unique CDC48 ortholog operates in a parasite mechanism responsible for G1 progression and is the first G1-specific checkpoint factor described in Toxoplasma. We describe transcriptome of the temperature sensitive mutant 11-104A4. Transcriptome studies demonstrated that gene expression is reflective of the parasite arrest in G1 phase. mRNAs normally upregulated in S/M phase were largely downregulated in the mutant at the restrictive temperature 40oC. Genetic complementation with extra copy of the wild type TgNoAP1 rescued growth of the mutant 11-104A4 at 40oC and reversed changes in the transcriptome.
Project description:Recent advances in high throughput sequencing methodologies allow the opportunity to probe in depth the transcriptomes of organisms including N. caninum and Toxoplasma gondii. In this project, we are using Illumina sequencing technology to analyze the transcriptome (RNA-Seq) of experimentally accessible stages (e.g. tachyzoites at different times points) of T. gondii VEG strain. The aim is to make comparative transcriptional landscape maps of Neospora and Toxoplasma at different time points at different life cycle stages and compare levels of expression of orthologous genes in these two organisms.
Project description:Toxoplasma gondii cell cycle mutant 11-104A4 reversibly arrests in the G1 phase. The defect in this mutant was mapped by genetic complementation to a gene encoding a novel AAA-ATPase/CDC48 family member (TgNoAP1). A change in a tyrosine to a cysteine upstream of an AAA+ domain leads to protein instability and results in cell cycle arrest. This factor is cell cycle regulated and exclusively expressed in the nucleolus during the G1/S phases. At high temperature the mutant quickly arrests with a single nucleus and expresses transcripts enriched in the G1 subtranscriptome. This unique CDC48 ortholog operates in a parasite mechanism responsible for G1 progression and is the first G1-specific checkpoint factor described in Toxoplasma. We describe transcriptome of the temperature sensitive mutant 11-104A4. Transcriptome studies demonstrated that gene expression is reflective of the parasite arrest in G1 phase. mRNAs normally upregulated in S/M phase were largely downregulated in the mutant at the restrictive temperature 40oC. Genetic complementation with extra copy of the wild type TgNoAP1 rescued growth of the mutant 11-104A4 at 40oC and reversed changes in the transcriptome. RNA samples were isolated in duplicate from mutant 11-104A4 parasites grown for 32h at permissive (34oC) or non-permissive temperatures (40oC). In addition, a duplicate sample of RNA from mutant 11-104A4 complemented with cosmid TOXOV53 encoding wild type copy of TgNoAP1 similarly grown at 40oC was collected. Samples were hybridized to the Toxoplasma gondii Affymetrix microarray (ToxoGeneChip: http://ancillary.toxodb.org/docs/Array-Tutorial.html). Hybridization data was preprocessed with Robust Multi-array Average (RMA) and normalized using per chip and per gene median polishing and analyzed using the software package GeneSpring GX (Agilent Technologies).