Abstract
Human cryptosporidiosis is caused primarily by two species of apicomplexan parasites, Cryptosporidium parvum and C. hominis. Although infection of cell monolayers with sporozoites does not support the complete parasite life cycle, the in vitro system is used to study the asexual phase of multiplication, which consists of two generations of merogony. To better understand host-parasite interaction and to gain insight into gene regulatory processes driving the complex life cycle of Cryptosporidium parasites, we analyzed the transcriptome of C. parvum in oocysts, sporozoites and infected cell monolayers 2–48 h post-infection. Analysis of RNA-Seq data from replicate oocyst, sporozoite and intracellular samples revealed significant differences between transcriptomes expressed outside and inside the host cell. Compared to the transcriptome found in the host cell, the oocyst transcriptome is less diverse. Biological processes significantly over-represented intracellularly relate to biosynthetic processes. Genes significantly overexpressed in oocysts show evidence of specialized functions not found in other Apicomplexa. A more comprehensive view of gene regulation during the Cryptosporidium life cycle will require the analysis of later time points during the infection, particularly of the poorly studied sexual phase of the life cycle.
Highlights
Cryptosporidiosis is recognized as one of the most common enteric infections in infants in sub-Saharan Africa and southeast Asia[1]
Reflecting the many technical obstacles to research on these parasites, published Cryptosporidium transcriptome analyses based on RNA-Seq are limited to one study of C. parvum extra- and intracellular gene expression in calf intestinal epithelium and in culture[9] and an analysis of the C. parvum life cycle transcriptome in organoids grown from small intestine and lung epithelial cells[7]
We identified functional categories overrepresented in the oocyst transcriptome and found these to be indicative of the specialized functions, like long-term survival and delivery of sporozoites into specific GI tract organs
Summary
Cryptosporidiosis is recognized as one of the most common enteric infections in infants in sub-Saharan Africa and southeast Asia[1]. Reflecting the many technical obstacles to research on these parasites, published Cryptosporidium transcriptome analyses based on RNA-Seq are limited to one study of C. parvum extra- and intracellular gene expression in calf intestinal epithelium and in culture[9] and an analysis of the C. parvum life cycle transcriptome in organoids grown from small intestine and lung epithelial cells[7]. With the goal of improving our understanding of gene regulation in Cryptosporidium parasites, we undertook an RNA-Seq analysis of the Cryptosporidium transcriptome at the oocyst, excysted sporozoite, and intracellular stages. Transcriptomic data of intracellular parasite stages indicate that the intracellular transcriptome is tailored for transcription and translation, consistent with rapid asexual multiplication during the initial phase of the infection. Compared to the difference between intra- and extracellular C. parvum transcriptome, differences in gene expression between oocysts and sporozoites were relatively small
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