Characterization of a putative hsp70 pseudogene transcribed in protoscoleces and adult worms of Echinococcus granulosus

Searching for hsp70 genes in Echinococcus granulosus, a divergent cytoplasmic hsp70-like sequence (EgψHsp70) was isolated, possessing a small truncation in the region coding for the C-terminal glycine-rich linker and EEVD-Ct motif. Southern Blot analyses of E. granulosus, and in silico analyses of E. multilocularis indicate that this truncated sequence is repeated several times in both genomes, in some cases containing clear cut features of pseudogenization. Phylogenetic analyses and comparison of surrounding regions indicate that all these copies originated by successive genomic duplications of one originally truncated copy. These copies are diverging at an increased rate compared to functional cytoplasmic hsp70 genes, and ratios of non-synonymous over synonymous substitutions rates (dN/dS) point to a relaxation of sequence constraint, suggesting that these sequences are pseudogenes. Interestingly, RT-PCR demonstrates that EgψHsp70 is transcribed in protoscoleces and adult individuals of E. granulosus. We suggest that this sequence does not code for a functional polypeptide, although some features are unexpected for a sequence evolving under a strictly neutral mode. Transcription could either be vestigial or have a specific, non-coding function.