SKSR1 identified as key virulence factor in Cryptosporidium by genetic crossing

Abstract

Cryptosporidium is a major cause of severe diarrhea. Although Cryptosporidium isolates exhibit significant differences in infectivity and virulence, the genetic determinants for these traits are not clear. In this study, we used classical genetics to cross two Cryptosporidium parvum isolates of different virulence and used bulked segregant analysis of whole-genome sequence data from the progeny to identify quantitative trait loci (QTL) associated with Cryptosporidium infectivity and virulence. Of the 26 genes in three QTL, two had loss-of-function mutations in the low-virulence isolates. Deletion of the SKSR1 gene or expression of the frame-shift mutant sequence reduced the pathogenicity of infection in vivo. SKSR1 is a polymorphic secretory protein expressed in small granules, secreted into the parasite-host interface, and may cooperate with other secretory proteins in pathogenesis. These results demonstrate that SKSR1 is an important virulence factor in Cryptosporidium, and suggest that the extended SKSR protein family, encoded by variant subtelomeric genes, may contribute to pathogenesis.