The apicomplexan parasites Plasmodium spp. are the causative agents of malaria, a disease that poses a significant global health burden. Plasmodium spp. initiate infection of the human host by transforming and replicating within hepatocytes. This liver stage (LS) is poorly understood compared to other Plasmodium life stages, which has hindered our ability to target these parasites for disease prevention.
Duke University researchers conducted an extensive transcriptome sequencing (RNA-Seq) analysis throughout the Plasmodium berghei LS, covering as early as 2 h postinfection (hpi) and extending to 48 hpi. Their data revealed that hundreds of genes are differentially expressed at 2 hpi and that multiple genes shown to be important for later infection are upregulated as early as 12 hpi. Using hierarchical clustering along with coexpression analysis, the researchers identified clusters functionally enriched for important liver-stage processes such as interactions with the host cell and redox homeostasis. Furthermore, some of these clusters were highly correlated to the expression of ApiAP2 transcription factors, while showing enrichment of mostly uncharacterized DNA binding motifs. This finding indicates potential LS targets for these transcription factors, while also hinting at alternative uncharacterized DNA binding motifs and transcription factors during this stage.
Coexpression analysis identifies enriched processes during
P. berghei development in hepatocytes
(A) Hierarchical clustering using a correlation distance with complete linkage of all genes significant (FDR ≤ 5%) in at least one of the analyses. Gene expression is z-score transformed. (B) GO enrichment analysis (biological process) of enriched clusters 3, 14, and 6. Representative GO terms (P < 0.01) and their respective number of genes (pie chart) are shown. The total numbers of genes in each cluster are shown at the center of the pie chart. (C) Spline models of gene expression data for all the genes in the top-scoring GO term in each cluster. Key genes in each group and their expression patterns are highlighted in red.
This work presents a window into the previously undescribed transcriptome of Plasmodium upon host hepatocyte infection to enable a comprehensive view of the parasite’s LS. These findings also provide a blueprint for future studies that extend hypotheses concerning LS gene function in P. berghei to human-infective Plasmodium parasites.