Abstract
BackgroundThe complex life cycle of malaria parasites requires well-orchestrated stage specific gene expression. In the vertebrate host the parasites grow and multiply by schizogony in two different environments: within erythrocytes and within hepatocytes. Whereas erythrocytic parasites are well-studied in this respect, relatively little is known about the exo-erythrocytic stages.MethodsIn an attempt to fill this gap, genome wide RNA-seq analyses of various exo-erythrocytic stages of Plasmodium berghei including sporozoites, samples from a time-course of liver stage development and detached cells were performed. These latter contain infectious merozoites and represent the final step in exo-erythrocytic development.ResultsThe analysis represents the complete transcriptome of the entire life cycle of P. berghei parasites with temporal detailed analysis of the liver stage allowing comparison of gene expression across the progression of the life cycle. These RNA-seq data from different developmental stages were used to cluster genes with similar expression profiles, in order to infer their functions. A comparison with published data from other parasite stages confirmed stage-specific gene expression and revealed numerous genes that are expressed differentially in blood and exo-erythrocytic stages. One of the most exo-erythrocytic stage-specific genes was PBANKA_1003900, which has previously been annotated as a “gametocyte specific protein”. The promoter of this gene drove high GFP expression in exo-erythrocytic stages, confirming its expression profile seen by RNA-seq.ConclusionsThe comparative analysis of the genome wide mRNA expression profiles of erythrocytic and different exo-erythrocytic stages could be used to improve the understanding of gene regulation in Plasmodium parasites and can be used to model exo-erythrocytic stage metabolic networks toward the identification of differences in metabolic processes during schizogony in erythrocytes and hepatocytes.
Highlights
The complex life cycle of malaria parasites requires well-orchestrated stage specific gene expression
The analysis represents the complete transcriptome of the entire life cycle of P. berghei parasites with tempo‐ ral detailed analysis of the liver stage allowing comparison of gene expression across the progression of the life cycle
Exo-erythrocytic form (EEF) parasites were isolated at different timepoints of infection by FACS sorting (6 h, 24 h, 48 h, 54 h and 60 h)
Summary
The complex life cycle of malaria parasites requires well-orchestrated stage specific gene expression. In the vertebrate host the parasites grow and multiply by schizogony in two different environments: within erythrocytes and within hepatocytes. The life cycle of Plasmodium parasites involves the injection of sporozoites into the vertebrate host during a blood meal of an infected female mosquito. For the rodent parasite Plasmodium berghei it has been shown that a proportion of injected sporozoites actively invade blood vessels and are passively transported to the liver [2]. After crossing the blood vessel endothelia in the liver to reach the parenchyma, the parasite transmigrates through several hepatocytes before it settles in one. Upon entry into the ultimate host cell, the host plasma membrane invaginates forming a parasitophorous vacuole (PV) in which the parasite resides, develops and multiplies by exo-erythrocytic schizogony
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