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Whole transcriptome analysis of rosetting Plasmodium falciparum parasites

ABSTRACT: Background: The cytoadherence of Plasmodium falciparum is thought to be mediated by variant surface antigens (VSA), encoded by var, rif, stevor and pfmc-2tm genes. The last three families have rarely been studied in the context of cytoadherence. As most VSA genes are unique, the variability among sequences has impeded the functional study of VSA across different P. falciparum strains. However, many P. falciparum genomes have recently been sequenced, allowing the development of specific microarray probes to each VSA gene. Methods: All VSA sequences from the HB3, Dd2 and IT/FCR3 genomes were extracted using HMMer. Oligonucleotide probes were designed with OligoRankPick and added to the 3D7-based microarray chip. As a proof of concept, IT/R29 parasites were selected for and against rosette formation and the transcriptomes of isogenic rosetting and non-rosetting parasites were compared by microarray. Results: From each parasite strain 50-56 var genes, 125-132 rif genes, 26-33 stevor genes and 3-8 pfmc-2tm genes were identified. The ability of the VSA-supplemented microarray chip to detect cytoadherence-related genes was assessed using P. falciparum clone IT/R29, in which rosetting is known to be mediated by PfEMP1 encoded by ITvar9. Whole transcriptome analysis showed that the most highly upregulated gene in rosetting parasites was ITvar9 (19 to 429-fold upregulated over six time points). Only one rif gene (IT4rifA_042) was upregulated by more than 4-fold (5-fold at 12 hours post-invasion), and no stevor or pfmc-2tm genes were upregulated by more than 2-fold. 49 non-VSA genes were upregulated in rosetting parasites by more than 3-fold in at least two time-points, although none as markedly as ITvar9. Conclusions: We demonstrate that the VSA of newly sequenced P. falciparum strains can be added to the 3D7-based microarray chip, allowing the analysis of the entire transcriptome of multiple strains. For the rosetting clone IT/R29, the striking transcriptional upregulation of ITvar9 was confirmed, and the data did not support the involvement of other VSA families in rosette formation.

ORGANISM(S): Plasmodium falciparum

PROVIDER: GSE28990 | GEO | 2011/07/01

SECONDARY ACCESSION(S): PRJNA140507

REPOSITORIES: GEO

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Project description:Background: The cytoadherence of Plasmodium falciparum is thought to be mediated by variant surface antigens (VSA), encoded by var, rif, stevor and pfmc-2tm genes. The last three families have rarely been studied in the context of cytoadherence. As most VSA genes are unique, the variability among sequences has impeded the functional study of VSA across different P. falciparum strains. However, many P. falciparum genomes have recently been sequenced, allowing the development of specific microarray probes to each VSA gene. Methods: All VSA sequences from the HB3, Dd2 and IT/FCR3 genomes were extracted using HMMer. Oligonucleotide probes were designed with OligoRankPick and added to the 3D7-based microarray chip. As a proof of concept, IT/R29 parasites were selected for and against rosette formation and the transcriptomes of isogenic rosetting and non-rosetting parasites were compared by microarray. Results: From each parasite strain 50-56 var genes, 125-132 rif genes, 26-33 stevor genes and 3-8 pfmc-2tm genes were identified. The ability of the VSA-supplemented microarray chip to detect cytoadherence-related genes was assessed using P. falciparum clone IT/R29, in which rosetting is known to be mediated by PfEMP1 encoded by ITvar9. Whole transcriptome analysis showed that the most highly upregulated gene in rosetting parasites was ITvar9 (19 to 429-fold upregulated over six time points). Only one rif gene (IT4rifA_042) was upregulated by more than 4-fold (5-fold at 12 hours post-invasion), and no stevor or pfmc-2tm genes were upregulated by more than 2-fold. 49 non-VSA genes were upregulated in rosetting parasites by more than 3-fold in at least two time-points, although none as markedly as ITvar9. Conclusions: We demonstrate that the VSA of newly sequenced P. falciparum strains can be added to the 3D7-based microarray chip, allowing the analysis of the entire transcriptome of multiple strains. For the rosetting clone IT/R29, the striking transcriptional upregulation of ITvar9 was confirmed, and the data did not support the involvement of other VSA families in rosette formation. Plasmodium falciparum parasites, strain IT/R29, were selected for (R29R+) or against (R29R-) rosetting. Both cultures (R29R+ and R29R-) were tightly synchronised before a timecourse experiment was performed. 6 samples, named time points 1 to 6, were taken every 8 hours. 12μg of RNA from the R29 non-rosetting parasites at each of the 6 time points was combined together to form the reference pool. The pool and 12μg of each individual time point sample from both rosetting and non-rosetting parasites were then used for cDNA synthesis. For microarray hybridizations,each cDNA sample was coupled to Cy5 (red dye) while Cy3 (green dye) was added to the pool. Cy5-labelled time point samples were mixed with the same amount of Cy3-labelled pool sample. The solution was loaded on a microarray slide and hybridized for 14–16 h.

Project description:Cerebral malaria is the most deadly manifestation of infection with Plasmodium falciparum. The pathology of cerebral malaria is characterised by the accumulation of infected erythrocytes in the microvasculature of the brain, due to parasite adhesins on the surface of infected erythrocytes binding to human receptors on microvascular endothelial cells. The parasite and host molecules involved in this interaction are unknown. We used the Human Brain Endothelial Cell line HBEC-5i to identify the malaria parasite ligands responsible for binding to human brain endothelial cells. Three P. falciparum strains (HB3, 3D7 and IT/FCR3) were selected for binding to HBEC5i and the whole transcriptome of selected and unselected parasites was analysed using a variant surface antigen-supplemented microarray chip. After selection, the only highly upregulated genes were a subset of group A-like var genes (HB3var3, 3D7_PFD0020c, ITvar7 and ITvar19), that showed 11 to >100-fold higher transcription levels in selected parasites. These genes are highly diverse in sequence, but do however show strong similarities in PfEMP1 architecture. Antibodies raised to the HB3var3 variant recognized the surface of infected erythrocytes and abolished the binding of infected erythrocytes to brain endothelial cells. The subset of Group A PfEMP1 variants identified here provides a new target for interventions to treat or prevent cerebral malaria. Unselected Plasmodium falciparum parasites (Uns) only poorly cytoadhere to human brain endothelial cells (HBEC-5i). Plasmodium falciparum HB3, 3D7 and IT/FCR3 strains were selected for binding to HBEC-5i (HB3-HBEC1, HB3-HBEC2, HB3-HBEC-TNF, 3D7-HBEC and IT-HBEC). HBEC-selected and unselected cultures were tightly synchronised before a timecourse experiment was performed. 6 samples, named time points 1 to 6, were taken every 8 hours. 12μg of RNA from the unselected parasites (HB3-Uns, 3D7-Uns or IT-Uns) at each of the 6 time points was combined together to form the reference pool. The pool and 12μg of each individual time point sample from both selected and unselectedparasites were then used for cDNA synthesis. For HB3-HBEC1 (pilot experiment), each HB3-HBEC1 time point (pilot experiment) was hybridised directly with HB3-Uns1 time points. For microarray hybridizations, each cDNA sample was coupled to Cy5 (red dye) while Cy3 (green dye) was added to the pool. Cy5-labelled time point samples were mixed with the same amount of Cy3-labelled pool sample. The solution was loaded on a microarray slide and hybridized for 14–16 h.

Project description:Purpose: In malaria parasites, the regulation of mRNA translation, storage and degradation is a critical aspect of gene expression, especially during the life stage transition. Since the DEAD-box helicases are involved in RNA metabolism, we wanted to determine whether pfdozi disruption led to altered mRNA abundance in P. falciparum. Methods: In this study, we functionally characterized the DEAD-box RNA helicase PfDOZI in the human malaria parasite Plasmodium falciparum and discovered its functions on mRNA metabolism during development. We generate a pfdozi gene knockout (KO) parasite line. 1). The transcriptomic analysis via RNAseq to the asexual parasites at four stages (ring, early trophozoite, late trophozoite, and schizont)(10h, 20h, 30h, and 40h post-invasion) and the sexual stage (gametocytes) between KO and wildtype (WT) 3D7 parasite line were performed in triplicate. Total RNA was isolated from the purified parasites using the Quick-RNA MiniPrep kit (Zymo Research). RNA sequencing libraries were prepared using the KAPA stranded RNA-seq library preparation kit (Roche) with 500 ng RNA from each sample. Illumina adapter sequence removal and quality trimming of reads were performed using Trimmomatic. Only reads that had a minimum length of 50 base pairs were retained. Reads were then mapped to the P. falciparum 3D7 strain reference genome with HISAT2. Differentially expressed genes are determined by DESeq2 with Padj < 0.01 and absolute log2 fold change higher than 1. 2). To investigate the function of pfdozi in stress response, both KO and WT parasites at the schizont stage were cultured under stress conditions. RNAs were harvested for the transcriptomic analysis via RNAseq. 3). To identify the mRNA targets of PfDOZI in schizonts and gametocytes, we performed RNA-immunoprecipitation (RIP) coupled with next-generation sequencing from the PfDOZI::GFP parasites. A gaussian mixture model with a set of stringent criteria, including a read-depth coverage greater than 10, a fold enrichment ratio greater than 2, and posterior probabilities higher than 0.95 in both replicates. Results: 1). RNA-seq analysis identified up-regulation of 18, 4, 7 and 130 genes and down-regulation of 104, 44, 28 and 15 genes in the Δpfdozi parasite compared to WT 3D7 (fold change ≥ 2 and adjusted P (Padj) < 0.01) at ring (10h), early trophozoite (20h), late trophozoite (30h) and schizont (40h) stage, respectively. Our results showed that pfdozi disruption led to the upregulation of invasion-related genes in schizonts; 2). RNA-seq analysis revealed that the effect of pfdozi disruption on gametocytes was substantially more profound than in asexual stages, with 842 downregulated and 752 upregulated transcripts (fold change ≥2, Padj < 0.01) in the Δpfdozi gametocyte. About 80% of these markedly reduced transcripts are gametocyte/ookinete-specific transcripts. Genes related to microtubule/cytoskeleton, cellular respiration, and crystalloid were significantly enriched among the downregulated genes, which agrees with the defective morphogenesis of the Δpfdozi gametocytes. 3). RNAseq analysis showed that under the stress conditions, the WT parasites showed three-fold more upregulated transcripts (591) than downregulated (149), suggesting that significantly more transcripts were protected from degradation under stress conditions. In contrast, the Δpfdozi parasites had a much higher proportion (57%, 463) of downregulated than that of upregulated transcripts (43%, 346) under such stress conditions. 4). The RIP-seq analysis collectively identified the potential target mRNAs of the PfDOZI complex(es) in P. falciparum schizonts and gametocytes, identified 823 and 1377 transcripts as potential target mRNAs of the PfDOZI complexes in schizonts and gametocytes, respectively. Our data also showed significant overlaps with genes whose expression was disturbed upon pfdozi disruption. Conclusions: Collectively, we have demonstrated that PfDOZI, likes its metazoan orthologs, is a versatile regulator of mRNA metabolism, and these functions are dynamically regulated during development with stage-specific characteristics.

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Whole transcriptome analysis of rosetting Plasmodium falciparum parasites

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