Analysis of the gene expression profile of Schistosoma mansoni cercariae using the expressed sequence tag approach

ESTs constitute rapid and informative tools with which to study gene-expres sion profiles of the diverse stages of the schistosome life cycle. Followin g a comprehensive EST study of adult worms, analysis has now targeted the c ercaria, the parasite larval form responsible for infection of the vertebra te host. Two Schistosoma mansoni cercarial cDNA libraries were examined and partial sequence obtained from 957 randomly selected clones. On the basis of database searches, 551 (57.6%) ESTs generated had no homologs in the pub lic databases whilst 308 (32.2%) were putatively identified, totaling 859 i nformative ESTs. The remaining 98 (10.2%) were uninformative ESTs (ribosoma l RNA and non-coding mitochondrial sequences). By clustering analysis we ha ve identified 453 different genes. The most common sequences in both librar ies represented Sm8 calcium binding protein (8% of ESTs), fructose-1,6-bisp hosphate aldolase. glyceraldehyde-3-phosphate dehydrogenase, cytochrome oxi dase subunit 1, ATP guanidine kinase and triose phosphate isomerase. One hu ndred and nineteen identified genes were sorted into 11 functional categori es, with genes associated with energy metabolism being the most abundant (1 3%) and diverse. The diversity and abundance of genes associated with the t ranscription:translation machinery and with regulatory:signaling functions were also marked. A paramyosin transcript was identified, indicating that t his gene is not exclusively expressed in adult worms and sporocysts (as had been suggested previously). The possible physiological relevance to cercar iae of the presence of transcripts with homology to calcium binding protein s of the EF-hand superfamily, Gq-coupled rhodopsin photoreceptor, rod phosp hodiesterase delta subunit and peripheral-type benzodiazepine receptor is d iscussed. (C) 1999 Elsevier Science B.V. All rights reserved.