Identification of Echinococcus granulosus microRNAs and their expression in different life cycle stages and parasite genotypes.

The aetiological agent of cystic hydatid disease, the platyhelminth parasite Echinococcus granulosus, undergoes a series of metamorphic events during its complex life cycle. One of its developmental stages, the protoscolex, shows a remarkable degree of heterogeneous morphogenesis, being able to develop either into the vesicular or strobilar direction. Another level of complexity is added by the existence of genotypes or strains that differ in the range of intermediate hosts where they can develop and form fertile cysts. These features make E. granulosus an interesting model for developmental studies. Hence, we focused on the study of the regulation of gene expression by microRNAs (miRNAs), one of the key mechanisms that control development in metazoans and plants and which has not been analysed in E. granulosus yet. In this study, we cloned 38 distinct miRNAs, including four candidate new miRNAs that seem to be specific to Echinococcus spp. Thirty-four cloned sequences were orthologous to miRNAs already described in other organisms and were grouped in 16 metazoan miRNA families, some of them known for their role in the development of other organisms. The expression of some of the cloned miRNAs differs according to the parasite life cycle stage analysed, showing differential developmental expression. We did not detect differences in the expression of the analysed miRNAs between protoscoleces of two parasite genotypes. This work sets the scene for the study of gene regulation mediated by miRNAs in E. granulosus and provides a new approach to study the molecules involved in its developmental plasticity and intermediate host specificity. Understanding the developmental processes of E. granulosus may help to find new strategies for the control of cystic hydatid disease, caused by the metacestode stage of the parasite.