Alternative splicing: a paradoxical qudo in eukaryotic genomes

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.

Complexity and the reductionism-holism debate in systems biology

Reductionism has largely influenced the development of science, culminating in its application to molecular biology. An increasing number of novel research findings have, however, shattered this view, showing how the molecular-reductionist approach cannot entirely handle the complexity of biological systems. Within this framework, the advent of systems biology as a new and more integrative field of research is described, along with the form which has taken on the debate of reductionism versus holism. Such an issue occupies a central position in systems biology, and nonetheless it is not always clearly delineated. This partly occurs because different dimensions (ontological, epistemological, methodological) are involved, and yet the concerned ones often remain unspecified. Besides, within systems biology different streams can be distinguished depending on the degree of commitment to embrace genuine systemic principles. Some useful insights into the future development of this discipline might be gained from the tradition of complexity and self-organization. This is especially true with regards the idea of self-reference, which incorporated into the organizational scheme is able to generate autonomy as an emergent property of the biological whole.