Project description:Plasmodium falciparum merozoite surface protein MSPDBL2 is a highly polymorphic target of naturally acquired immune responses encoded by a single copy gene under strong balancing selection in natural populations. The MSPDBL2 protein is expressed in only a minority of mature schizonts of any cultured parasite line, and mspdbl2 gene expression in culture is increased in response to overexpression of the gametocyte development inducer GDV1 in an engineered parasite clone, so there is a need to characterise its natural expression variation. In this study, MSPDBL2 in mature schizonts was analyzed in the first ex vivo culture cycle of 102 clinical isolates from four endemic populations in different West African countries, by immunofluorescence microscopy with antibodies against a conserved region of the protein. In most isolates, less than 1% of mature schizonts were positive for MSPDBL2 (median of 0.6% overall), but the frequency distribution was highly skewed as eleven isolates had more than 3% schizonts positive and one had 73% positive. The expression frequencies were similar across the four endemic populations, and there was no significant difference between the clinical isolates overall and frequencies of positive schizonts previously seen in cultured P. falciparum laboratory lines. To explore whether expression of other gene loci correlated with MSPDBL2 expression, whole transcriptome sequencing was performed on schizont-enriched material from 17 of the clinical isolates with a wide range of proportions of schizonts positive. Transcripts of particular parasite genes were highly significantly positively correlated with MSPDBP2 positivity in schizonts as well as with mspdbl2 gene transcript levels, with overrepresentation of many genes previously implicated as likely to be involved in gametocytogenesis, but not including other genes including the gametocytogenesis master regulator ap2g. Although MSPDBL2 expression occurs in a highly variable proportion of schizonts in clinical isolates, and correlation with expression of some gametocytogenesis-related genes is consistent with regulation by GDV1, it is not apparently a direct marker of sexual commitment and its function in the parasite remains to be determined.

Project description:Mechanisms regulating gene expression in malaria parasites are not well understood. Little is known about how this parasite regulates its gene expression during transition from one developmental stage to another and in response to various environmental conditions. Parasites in a diseased host face environments which differ from the static, well adapted in vitro conditions in culture. Parasites thus need to adapt quickly and effectively to these conditions by establishing transcriptional states which is best suited for better survival. With the discovery of natural antisense transcripts (NATs) in this parasite and considering the various proposed mechanisms by which NATs might regulate gene expression, it has been speculated that these might be playing a critical role in gene regulation. We report here the diversity of NATs that exist in this parasite, using isolates taken directly from patients with differing clinical symptoms caused by malaria infection. A total of 797 NATs targeted against annotated loci have been detected using a custom designed strand specific microarray. Out of these, 545 are unique to this study. The majority of NATs were positively correlated with the expression pattern of the sense transcript. Many were found to be differentially regulated in response to disease conditions. Antisense transcripts mapped to a wide variety of biochemical/ metabolic pathways, especially pathways pertaining to the central carbon metabolism and stress related pathways. Our data strongly suggests that a large group of NATs detected here are unannotated transcription units antisense to annotated gene models. The results reveal a previously unknown set of NATs that prevails in this parasite, their differential regulation in disease conditions and mapping to functionally well annotated genes. The results detailed here call for studies to deduce the possible mechanism of action, which would help in understanding the in vivo pathological adaptations of these parasites. Plasmodium falciparum isolates were collected from patients (n = 11) with differing clinical conditions.The patients exhibited symptoms categorized as un-complicated (n =2) or complicated malaria (n = 9). Criteria for determination of complicated disease were based on World Health Organization year 2000 guidelines. Microarray array based transcriptional profiling was carried out to detect prevalence of natural antisense transcript.

Project description:Genomic variation is an inherent phenomena observed among members of same species belonging to different geographical locations. In case of P. falciparum, an apicomplexan protozoan parasite, its 22.8 MB nuclear genome is known to display vast genetic diversity in the subtelomeric compartments having but not exclusively variant gene families like var, rifins and stevors and examples in other elements of the genome have recently been documented. Microarrays, relies solely on the genomic sequence information to capture the relevant transcript abundance and needs to consider these variations into account for revealing true transcriptional variation.Here, we describe the designing strategy of a custom P. falciparum 15K array using Agilent platform to study the transcriptome of Indian field isolates for which genome sequence information is limited. Array contains probes representing genome sequence of two distinct geographical isolates (i.e 3D7 and HB3) and subtelomeric var gene sequence of a third isolate (IT4) known to adhere in culture condition. Probes in the array have been selected based on their efficiency to detect transcripts by performing a 244K array experiment representing multiple probes per gene/transcript. Array performance was evaluated and validated using RNA materials from P. falciparum clinical isolates obtained directly from patients with differing clinical conditions due to malaria infection.Due to pre probe screening large percentage (91 %) of the represented transcripts could be detected from Indian P. falciparum isolates. Replicated probes and multiple probes representing the same gene showed perfect correlation between them suggesting good probe performance. Additional transcripts could be detected due to inclusion of unique probes representing HB3 strain transcripts. Variant surface antigen (VSA) transcripts were detected by optimized probes representing the VSA genes of three geographically distinct strains. Plasmodium falciparum isolates were collected from patients (n=13) with differing clinical conditions. The patients exhibited symptoms categorized as uncomplicated (n=6) or complicated malaria (n=7). Criteria for determination of complicated disease were based on World Health Organization year 2000 guidelines. Microarray array based transcriptional profiling was carried out to evaluate the performance of the array.

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Plasmodium falciparum

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