Transcriptome analysis of Plasmodium berghei during its exo-erythrocytic development

One of the biggest challenges for vaccine and drug development in the malaria field is to identify appropriate target genes in the genome of the parasite Plasmodium. Ideally, target candidates should have an essential function during one or more life cycle stages. Another important challenge is to define the role of numerous genes with still an unknown function. To provide a basis for these challenges, we performed RNA-seq analysis of various exo-erythrocytic parasite stages including sporozoites, several liver stages and detached cells, which contain infectious merozoites and thus represent the final step in liver stage development. The time course transcriptome analysis presented here completes for the first time the transcriptome of the entire life cycle of a Plasmodium parasite and will thus be very useful for the malaria community to study gene regulation of this parasite and to identify candidates for the generation of genetically attenuated parasites. We have used these RNA-seq data to cluster genes with similar expression profiles, which might give a hint of their function. A comparison with already published data of other parasite stages revealed numerous genes that are expressed differently in blood and liver stages. We finally searched for genes that have a similar mRNA expression profile as two genes that code for proteins known to be involved in parasite egress, plasmepsin X and subtilisin 1. We reasoned that some co-expressed candidate gene products might be involved in the regulation of egress and invasion.