Cryptosporidium parvum genes containing thrombospondin type 1 domains

Cryptosporidium parvum is recognized as an enteropathogen of great worldwide medical and veterinary importance, yet understanding of its pathogenesis has been hampered in part by limited knowledge of the invasion machinery of this parasite. Recently, genes containing thrombospondin type I (TSPI) domains have been identified in several genera of apicomplexans, including thrombospondin-related adhesive proteins (TRAPs) that have been implicated as key molecules for parasite motility and adhesion onto host cell surfaces. Previously, a large-scale random survey of the C parvum genome conducted in our laboratory revealed the presence of multiple genomic DNA sequences with a high degree of similarity to known apicomplexan TRAP genes. In the present study, TBLASTN screening of available C parvum genomic sequences by using TSPI domains as queries identified a total of 12 genes possessing TSPI-like domains. All genes have putative signal peptide sequences, one or more TSPI-like domains, plus additional extracellular protein modules such as Kringle, epidermal growth factor, and Apple domains. Two genes, putative paralogs CpTSP8 and CpTSP9, contain predicted introns near their amino termini, which were verified by comparing PCR products from cDNA versus genomic DNA templates. Reverse transcription-PCR analysis of transcript levels reveals that C. parvum TSP genes were developmentally regulated with distinct patterns of expression during in vitro infection. TRAPC1, CpTSP3, and CpTSP11 were expressed at high levels during both early and late stages of infection, whereas CpTSP2, CpTSP5, CpTSP6, CpTSP8, and CpTSP9 were maximally expressed during the late stages of infection. Only CpTSP4 was highly expressed solely at an early stage of infection.