Analysis of Schistosoma mansoni genes using the expressed sequence tag approach

Expressed sequence tags (ESTs) are partial cDNA sequences read from both ends of random expressed gene fragments used for discovering new genes. DNA libraries from four different developmental stages of Schistosoma mansoni used in this study generated 141 ESTs representing about 2.5% of S. mansoni sequences in dbEST. Sequencing was done by the dideoxy chain termination method. The sequences were submitted to GenBank for homology searching in nonredundant databases using Basic Local Alignment Search Tool for DNA (BLASTN) alignment and for protein (BLASTX) alignment at the National Center for Biotechnology Information (NCBI). Among submitted ESTs, 29 were derived from lambdagt11 sporocyst library, 70 from lambdaZap adult worm library, 31 from lambdaZap cercarial library, and 11 from lambdaZap female B worm library. Homology search revealed that eight (5.6%) ESTs shared homology to previously identified S.mansoni genes in dbEST, 15 (10.6%) are homologous to known genes in other organisms, 116 (81.7%) showed no significant sequence homology in the databases, and the remaining sequences (2.1%) showed low homologies to rRNA or mitochondrial DNA sequences. Thus, among the 141 ESTs studied, 116 sequences are derived from noval, uncharactarized S. mansoni genes. Those 116 ESTs are important for identification of coding regions in the sequences, helping in mapping of schistosome genome, and identifying genes of immunological and pharmacological significance.