Several genes related to the ubiquitin (Ub)-proteasome pathway, including those coding for proteasome subunits and conjugation enzymes, are differentially expressed during the Schistosoma mansoni
life cycle. Although deubiquitinating enzymes have been reported to be negative regulators of protein ubiquitination and shown to play an important role in Ub-dependent processes, little is known about their role in S. mansoni
. In this study, we analysed the Ub carboxyl-terminal hydrolase (UCHs) proteins found in the database of the parasite's genome. An in silico ana-
lysis (GeneDB and MEROPS) identified three different UCH family members in the genome, Sm
UCH-L5 and Sm
BAP-1 and a phylogenetic analysis confirmed the evolutionary conservation of the proteins. We performed quantitative reverse transcription-polymerase chain reaction and observed a differential expression profile for all of the investigated transcripts between the cercariae and adult worm stages. These results were corroborated by low rates of Z-Arg-Leu-Arg-Gly-Gly-AMC hydrolysis in a crude extract obtained from cercariae in parallel with high Ub conjugate levels in the same extracts. We suggest that the accumulation of ubiquitinated proteins in the cercaria and early schistosomulum stages is related to a decrease in 26S proteasome activity. Taken together, our data suggest that UCH family members contribute to regulating the activity of the Ub-proteasome system during the life cycle of this parasite.