Diverse single-amino-acid repeat profiles in the genus Cryptosporidium

Comparative genomic analysis of the principal Cryptosporidium species that infect humans

Cryptosporidium parasites are ubiquitous and can infect a broad range of vertebrates and are considered the most frequent protozoa associated with waterborne parasitic outbreaks. The intestine is the target of three of the species most frequently found in humans: C. hominis, C. parvum, and. C. meleagridis. Despite the recent advance in genome sequencing projects for this apicomplexan, a broad genomic comparison including the three species most prevalent in humans have not been published so far. In this work, we downloaded raw NGS data, assembled it under normalized conditions, and compared 23 publicly available genomes of C. hominis, C. parvum, and C. meleagridis. Although few genomes showed highly fragmented assemblies, most of them had less than 500 scaffolds and mean coverage that ranged between 35X and 511X. Synonymous single nucleotide variants were the most common in C. hominis and C. meleagridis, while in C. parvum, they accounted for around 50% of the SNV observed. Furthermore, deleterious nucleotide substitutions common to all three species were more common in genes associated with DNA repair, recombination, and chromosome-associated proteins. Indel events were observed in the 23 studied isolates that spanned up to 500 bases. The highest number of deletions was observed in C. meleagridis, followed by C. hominis, with more than 60 species-specific deletions found in some isolates of these two species. Although several genes with indel events have been partially annotated, most of them remain to encode uncharacterized proteins.

Characterization of MEDLE-1, a protein in early development of Cryptosporidium parvum

Background

Cryptosporidium spp. are important diarrhea-causing pathogens in humans and animals. Comparative genomic analysis indicated that Cryptosporidium-specific MEDLE family proteins may contribute to host adaptation of Cryptosporidium spp., and a recent study of one member of this family, CpMEDLE-2 encoded by cgd5_4590, has provided evidence supporting this hypothesis. In this study, another member of the protein family, CpMEDLE-1 of Cryptosporidium parvum encoded by cgd5_4580, which is distinct from CpMEDLE-2 and has no signature motif MEDLE, was cloned, expressed and characterized to understand its function.

Methods

CpMEDLE-1 was expressed in Escherichia coli and polyclonal antibodies against the recombinant CpMEDLE-1 protein were prepared in rabbits. Quantitative PCR was used to analyze the expression profile of cgd5_4580 in C. parvum culture. Immunofluorescence staining was used to locate CpMEDLE-1 expression in life-cycle stages, and in vitro neutralization assay with antibodies was adopted to assess the role of the protein in C. parvum invasion.

Results

The results indicated that cgd5_4580 had a peak expression at 2 h of C. parvum culture. CpMEDLE-1 was located in the mid-anterior region of sporozoites, probably within the dense granules. The neutralization efficiency of anti-CpMEDLE-1 antibodies was approximately 40%.

Conclusions

The differences in protein and gene expression profiles between CpMEDLE-1 and CpMEDLE-2 suggest that MEDLE proteins have different subcellular locations, are developmentally regulated, could be potentially involved in the transcriptional regulation of the expression of parasite or host proteins and may exert their functions in different stages of the invasion and development process.