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 1 (TSP1) 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 TSP1 domains as queries identified a total of 12 genes possessing TSP1-like domains. All genes have putative signal peptide sequences, one or more TSP1-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.Although its association with human diseases was not perceived until 1976 (18, 27, 31), the apicomplexan parasite Cryptosporidium parvum has emerged as a significant pathogen both of humans and animals of veterinary importance. The parasite primarily infects the epithelial cells of the small intestine and causes gastrointestinal diseases in both immunocompetent and immunocompromised humans and animals. Typically self-limiting in immunologically healthy individuals, cryptosporidial infection can be persistent and life-threatening in hosts with impaired immune systems. Prolonged infection is compounded by the fact that there is currently no effective anticryptosporidial drug (19). Efforts to develop novel therapeutic strategies have been hampered by a lack of understanding of C. parvum pathogenesis and a paucity of stage-and organelle-specific markers with which to dissect the parasite's life cycle.Thrombospondin-related adhesive proteins (TRAPs) have been identified in several genera of apicomplexans, including TRAP (38,39,45,53) and CTRP (13, 54, 57, 60, 61) of Plasmodium, Etp100 of Eimeria (10, 32, 56), MIC-2 of Toxoplasma (2, 20), and NcMIC2 of Neospora (24, 46) spp. TRAPs are characterized by the presence of two adhesive modules: one or more von Willebrand factor A (vWA)-like domai...