Expanding the size limit of RNA viruses: Evidence of a novel divergent nidovirus in California sea hare, with a ~35.9 kb virus genome

Humberto J Debat

californica and its well-studied neurons offer an exceptional technical platform for RNA dynamics (Puthanveettil et al., 2013; Moroz & Kohn, 2010 -2013 . To tentatively assess cell/tissue and organ tropism based on virus-derived RNA accumulation in A. californica, . CC-BY-NC-ND 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/307678 doi: bioRxiv preprint available California sea hare RNAseq libraries were mapped to AcNV and normalized as Fragments Per Kilobase of transcript per Million mapped reads (FPKM). Virus RNA transcripts were detected in an outstanding diversity of target tissue and organs, suggesting e pervasive tissue tropism of AcNV (Fig 2; Supp. Table 3 ). At the adult organ level (Fig 2. A, B right panel) AcNV was detected in chemoreceptive areas (rhinophores & tentacles), salivary glands, gills, heart, additional muscles (body wall, buccal and penial), hermaphroditic glands, ovotestis, hepatopancreas and other digestive glands. Interestingly, AcNV appeared to be highly enriched in the CNS. The availability of CNS tissue and single-cell RNAseq data allowed the surveillance of specific tropism at the cellular level of AcNV (Fig 2.B-E) . AcNV accumulated at relatively higher levels in the left excitatory interneuron 29 (L29), the left motor neuron 7 (L7), the right serotonergic cerebral ganglion metacerebral neuron (MCC-R) and the right abdominal ganglion cholinergic neuron 2 (R2). The R2 neuron and its axonal pathway is highly conserved and thus can be consistently identified in closely related species of the genus Aplysia.