Analysis of messages expressed by Echinostoma paraensei miracidia and sporocysts, obtained by random EST sequencing

A lambda ZAP Express cDNA library was constructed with mRNA obtained from i mmature miracidia within eggs, hatched miracidia, and sporocysts of Echinos toma paraensei. This cDNA library was amplified and 213 expressed sequence tag (EST) sequences (averaging 466 nucleotides in length) were obtained. Th e mean percentage of unresolved bases within the EST sequences was 0.4%, ra nging from 0 to 4.6%. The 213 ESTs represent 151 unique messages. BLAST (ve rsion 2.0.8) analysis disclosed that 64 unique E. paraensei messages (42.4% ) had significant similarities (BLAST score less than or equal to e-5), at deduced amino acid or nucleotide levels, with known sequences in the nonred undant GenBank databases or the dbEST database (NCBI). The remainder, 57.6% of the unique EST-encoded messages, scored nonsignificant hits. Most of th e E. paraensei messages that could be assigned a cellular role based on seq uence similarities were involved in gene/protein expression. Several ESTs s cored highest similarities with sequences obtained from trematode species. A total of 22,560 nucleotides present in open reading frames from ESTs that aligned with known sequences was used to determine codon usage for E. para ensei. Analysis of a subset of eight ESTs that contained full-length open r eading frames did not reveal a bias in codon usage. Also, EST sequences wer e found to contain 3' untranslated regions with an average length of 69.9 /- 88.4 nucleotides (n = 46). The EST sequences were submitted to GenBank/d bEST, adding to the 51 available Echinostoma-derived sequences, to provide reference information for both phylogenetic analysis and study of general t rematode biology.