The transcriptional landscape of the nervous system of Octopus vulgaris

Cephalopoda, a class of the phylum Mollusca, has undergone dramatic evolutionary changes in the body plan and in the morphology of the nervous system. The complexity of the nervous system can be recognized from the brain size, the number of neuronal cells and the neuroanatomical organization and it is comparable to that of vertebrates. In the Octopus vulgaris, the nervous system reaches a great level of complexity both in the Central nervous system (CNS) and Peripheral nervous system (PNS). The aim of the my PhD is to generate the reference transcriptome of the nervous system to understand, at the molecular level, its organization, development and evolution, allowing comparative analysis across both the different areas as well as multiple animal phyla. The Octopus transcriptome sequencing allowed me to show, for the first time, an unexpected high frequency of retroelements embedded in transcripts, much more similar to that shown in mammals and much higher than in other invertebrate and vertebrate non-mammalian species. Interestingly, Short INterspersed Elements (SINEs) are significantly more abundant in long noncoding RNAs (lncRNAs) than in protein coding genes, and both lncRNAs and SINEs are enriched in transcripts expressed in the central nervous system (CNS). Moreover, in this study I also identified a Long INterspersed Element (LINE) that is transcribed in the CNS and seems to be fully competent for the retrotransposition of itself and its partner SINE. These observations suggest a possible convergent evolutionary scenario involving retroelements and lncRNAs pervasive expression in the Octopus nervous system, contributing to develop its cognitive abilities, unique among invertebrates.