Introduction
Pacific oysters (Crassostrea gigas) are one of the most important aquaculture species globally . Sustainable production of oysters is hampered by outbreaks of mass mortality caused by Oyster Herpes Virus (OsHV). Better understanding of the genetics underlying resistance to OsHV is essential to preventing future outbreaks, as vaccination or treatments are not feasible in the field, leaving biosecurity as the main defence. Furthermore, it is important to consider the full range of life stages of the oyster as they are exposed to OsHV throughout their life.
The aim of this study was to use whole-tissue explants challenged with OsHV to determine gene expression changes in different tissues and at different life stages. This data can then be used to inform selective breeding or gene editing approaches to enhancing OsHV resistance.
Materials and methods
Live pacific oysters from three key life stages (spat <2cm, juvenile 5-6cm , and adult >15cm ) are obtained from a UK oyster farm. Heart, mantle, muscle and gill tissues are dissected and sterilized using antibiotic and antifungal treatments under sterile conditions. Tissues were cultured in custom media. OsHV was added to challenge groups. RNA and DNA were extracted from samples across 96 hours. RNAseq and qPCR were used to quantify gene expression.
Discussion and future work
The development of a system for maintaining whole tissues from pacific oysters is an exciting development that has been investigated for the first time (Potts et al. 2020). This system facilitates investigation into the host genetic response to infection at different life stages and backgrounds of disease resistance (Degremont et al 2021) . Elucidation via qPCR and RNAseq will reveal genes of interest as potential targets for genome editing. Furthermore, tissue specific responses will be valuable for better understanding OsHV virology. Key questions to address are the main site of OsHV replication within the oyster and potential sites for virus latency or senescence. Additionally, this approach may enable the complete OsHV lifecycle in the laboratory, which has not been achieved to date.
References
Potts, R. W. A., Gutierrez, A. P., Cortés-Araya, Y., Houston, R. D., Bean, T. P. 2020 Developments in marine invertebrate primary culture reveal novel cell morphologies in the model bivalve Crassostrea gigas. PeerJ. 8, e9180. (doi:10.7717/peerj.9180)
LionelDégremon t, BenjaminMorga, EliseMaurouar d, Marie-AgnèsTraver s. 2021 Susceptibility variation to the main pathogens of Crassostrea gigas at the larval, spat and juvenile stages using unselected and selected oysters to OsHV-1 and/or V. aestuarianus . Journal of Invertebrate Pathology Volume 183, July 2021, 107601