Santiago de Compostela, 2 November 2021. The Spanish National Research Council (CSIC), through the Immunology and Genomics group of the Institute of Marine Research (IIM), has supervised a doctoral thesis whose results make it possible to advance new strategies for controlling viral diseases in aquaculture, specifically nodavirus in European seabass.
The author, Raquel Lama López, carried out the research under the supervision of Beatriz Novoa García, CSIC research professor and head of the aforementioned research group. The thesis, “Search for new strategies for controlling viral diseases in aquaculture”, was part of the PhD Programme in Advances in Microbial and Parasitic Biology at the University of Santiago de Compostela and had Mª Isabel Santos Rodríguez as tutor. It was recently defended and received the grade of outstanding with “cum laude” and “international” mentions.
“Spain ranks fourth in the world ranking for seabass fishing and third in aquaculture production of this species. Seabass is affected by infectious diseases of all kinds, the one causing the greatest losses being viral retinopathy and encephalopathy, whose causative agent is nervous necrosis virus, known as nodavirus. It mainly affects the central nervous system and can cause up to 100% mortality in juveniles. The pathological anatomy of infected individuals reveals extensive necrosis of the central nervous system, with vacuolisation and neuronal degeneration in the brain and retina. This damage causes clinical signs that are very characteristic of the disease, such as abnormal swimming behaviour: infected individuals show hyperinflation of the swim bladder and swim in downward spiral movements, curving their spine, which causes total disorientation in swimming. They also become darker and lose their appetite,” CSIC explains.
“There are currently only two vaccines on the market against the RGNNV genotype. For now, the virus is being tackled through extreme prevention measures, avoiding crop exposure and reinforcing good management practices,” explains Raquel Lama, who adds that “the innate immune response is considered essential for dealing with a viral infection”.
In this context, the general objective of the thesis was to explore the response of seabass to nodavirus infection. To this end, the global transcriptome of this nodavirus-infected species was studied using RNAseq, revealing a strong stress response. “It is also interesting to highlight the possible role of lncRNAs (areas of the genome/transcriptome that until now were thought to have no specific role in the cell) in modulating the transcriptomic response, and the fact that a vaccine consisting of a fragment of a betanodavirus protein expressed on the surface of bacteria was successfully used,” the thesis author highlights.
The research used different bioinformatic methodologies to study interactions between seabass and nodavirus (host and pathogen, respectively). For this purpose, the complete transcriptomic response of seabass to nodavirus was analysed using the RNA-Seq technique, as well as its possible modulation by non-coding RNAs in the genome (lncRNAs), choosing the brain and kidney as study subjects.
“This is the first time that the complete transcriptomic response of seabass to a nodavirus infection has been analysed. An interaction between the neuroendocrine system and the immune system was observed through the hypothalamic-pituitary-interrenal axis during nodavirus infection. On the other hand, we have described how different lncRNAs could be modulating this transcriptomic response. Furthermore, as a consequence of the neurotropic nature of nodavirus, the response was greater in the brain than in the kidney,” highlights Raquel Lama.
The thesis also developed a prototype seabass vaccine against nodavirus characterised mainly by improved safety and environmental performance, since it does not require adjuvants.
“There are four genotypes within the genus to which nodavirus belongs, classified according to the gene sequence encoding protein C. Most vaccines described to date against nodavirus are characterised by using the complete or inactivated virus and by being based on empty capsids, recombinant protein C or synthetic peptides derived from protein C,” says Raquel Lama.
“ Finally, given the relative difficulty of working with species of high commercial value, we established zebrafish as a model for nodavirus infection. This made it possible to determine that the older the larvae were, the more difficult it was for them to show symptoms of infection, and that higher mortality of infected larvae correlated with greater expression of the nodavirus capsid protein over time,” says Raquel Lama.
“This reaffirms the basis for considering zebrafish as an infection model, not only for nodavirus but also for many other fish viruses that are difficult to study in vivo because of the difficulties in obtaining affected species from the market or maintaining them in the laboratory. Developing a model that enables us to learn more quickly and easily about the mechanisms through which a virus that damages the central nervous system, such as nodavirus, acts opens the door to comparing its mechanisms of action with those of viruses that cause encephalopathies in humans, such as herpes simplex virus or varicella zoster virus, and even with the typical development of neurodegenerative diseases such as Alzheimer’s, and thus to testing therapies that allow us to address common neurodegenerative processes,” she concludes.
The author
Raquel Lama López (Pazos-Hermos, Ourense, 1990) holds a degree in Biology (2008-2013), a Master’s degree in Biotechnology (2013-2015) and a PhD in Biology from the University of Santiago de Compostela (2021).
She has experience in international laboratories: the School of Life Sciences at the Gwangju Institute of Science and Technology (GIST, South Korea, 2014), the Nanomedicine Area at the International Iberian Nanotechnology Laboratory (INL, Portugal, 2015), and the Aquaculture Biotechnology and Genomics Laboratory at the Biotechnology Centre of the University of Concepción (INCAR, Chile, 2018).
She is currently employed by the Immunology and Genomics group of IIM-CSIC, where she is involved in research related to fish antiviral responses and aquaculture health.