Genome-wide transcriptome analysis of the early developmental stages of Echinococcus granulosus protoscoleces reveals extensive alternative splicing events in the spliceosome pathway.

BACKGROUND

The complex life cycle of Echinococcus granulosus involves numerous environmental conditions within different intermediate and definitive hosts. This requires adaptation at different levels of transcript regulation. Alternative splicing (AS) and the related cellular functions as one of the major fields of post-genomics has been poorly studied in tapeworms. In the present study, we investigated AS events and their potential biological effects in E. granulosus.

METHODS

Whole transcriptome sequencing data of four groups of protoscoleces were prepared for RNA-seq library construction. Fresh protoscoleces were either used as non-induced controls (NT group) or incubated for 15 min with pepsin (PEP group) and cultivated in a biphasic medium for 12 and 24 h (12 and 24 h groups). The frequency and different types of AS events were identified using rMATS software. Functional annotations and gene ontology of differential AS (DAS) genes were performed using Blast2GO software. AS events were experimentally validated by PCR on the protoscolex cDNAs using specific primers for each gene.

RESULTS

At least one AS event was found in 38.1% of the genes (3904 out of 10,245) in the protoscoleces during early strobilar development. The genes were associated primarily with cellular and metabolic processes and binding and catalytic activity. KEGG pathway analysis of DAS events revealed a number of genes belonging to different components of the spliceosome complex. These genes tended to belong to common SR proteins, U1-related factors, U2-related factors, complex A-specific factors and other splicing-related proteins.

CONCLUSIONS

The high number of AS events in the transcriptome regulatory mechanisms indicates the essential rapid molecular processes required by the parasite for adaptation in different environments.