Cloning of developmentally regulated genes from Schistosoma mansoni

Schistosoma mansoni is a parasitic helminth that is notable for the number of developmental forms that it assumes during its lifecycle. In order to isolate genes that are developmentally regulated during this life cycle, I constructed cDNA libraries from mRNA isolated from the cercarial, sporocyst and adult stages of the organism. These libraries were differentially screened using labelled whole cDNA from various stages. Plaques hybridizing to labelled cDNA from one stage but not another were isolated and amplified. Using a complementary technique, I screened expression libraries with antisera from chronically infected humans in order to isolate genes encoding antigens of potential immunologic relevance. These were examined by northern blotting to determine which might be regulated. Four developmentally regulated genes have been isolated. SMA22.6 encodes a 0.95 kb mRNA that transcribed in both male and female adults. It hybrid-selects a 22 kDa polypeptide. The cDNA of this clone was used to construct a fusion protein in E. coli, and rabbit antisera against this fusion protein specifically stains the adult tegument. F523A encodes a female-specific 1 kb mRNA that is present in gravid females but absent in males and in immature or unfertilized females. Its sequence shows homology to the chorion proteins of Drosophila. SMC74 encodes a cercaria-specific 2.4 kb mRNA that present in cercaria and schistosomula, but is absent in adults and other stages. By hybrid-selection/in vitro translation, it encodes a 74 kDa polypeptide. DNA sequencing demonstrates it to have a high degree of homology with creatine kinase. Finally, I(H)B encodes a 1.5 kb mRNA that is present in cercariae, young schistosomula, eggs and adults, but disappears in schistosomula cultured for 3 hours or more. It hybrid selects a 92 kDa in vitro translation polypeptide. Using these clones as probes I have studied the early events in the transformation of the cercaria to the schistosomulum.