Female-specific sequences isolated from Schistosoma mansoni by representational difference analysis.

Representational difference analysis (RDA), a recently described, polymerase-chain-reaction-based modification of the subtractive hybridization process was employed to isolate female-specific sequences of Schistosoma mansoni. Using HindIII-derived amplicons, an excess of male schistosome DNA was employed to remove sequences common to both male and female adult S. mansoni genomes from female genomic DNA. Following three rounds of RDA, the enriched sequences included two female-specific repetitive elements. One of these exhibited 76% homology to the SM alpha family of retroposons and represents a W chromosome-specific variant of that family. The other sequence represents a novel, female-specific repetitive sequence. These sequences have been designated SM alpha fem-1 and W2, respectively, and both are apparently arrayed as tandem repeats on the W chromosome of S. mansoni. The isolation and characterization of the two female-specific sequences by RDA indicates that this procedure should also find utility in the definition of traits and sequences that differ among other groups of schistosomes.