Schistosoma mansoni: the varying occurrence of repetitive elements in different strains shows sex-specific polymorphisms.

The repetitive elements W1, W2, and D9 were shown before to be female specific in the Puerto Rican strain of Schistosoma mansoni. In the Liberian strain, however, W1 was detected in both sexes. Therefore, a strain- and sex-specific analysis of the presence of all three repetitive elements has been performed in different schistosome strains. For this analysis, W2 has been isolated and characterized, whereas W1 and D9 were already available. We demonstrate the presence of the W2 element in both sexes in the Liberian strain, which coincides with W1. Furthermore, it is shown that elements W1 and W2, but not D9, can be found in both sexes of the majority of the other strains investigated. We even found an isolate of the Puerto Rican strain with W1 and W2 elements in females and males. This finding contradicts results reported in the literature that demonstrated that W1 and W2 are female specific for the Puerto Rican strain. The data of this study indicate sex-specific polymorphisms, probably associated with the sex chromosomes in schistosomes.