RTG-TOF, a rainbow trout (Oncorhynchus mykiss) cell line with an inducible gene expression system

Research on non-mammalian vertebrate models, due to the small size of the scientific community and the diversity of species under investigation, suffers from a paucity of basic reagents such as monoclonal antibodies and cell lines. Such tools facilitate functional characterisation of physiological processes, including fish-pathogen interactions. The knowledge gap in fish research has been narrowed in recent years with development of high-quality annotated genomes for several fish species of economic importance. Nevertheless, additional tools are still required to identify the function of newly annotated genes, in particular specific functions of paralogs that arise from teleost- or salmonid-specific whole-genome duplication. Loss of function by genome editing (Dehler et al. 2016, 2019) or gene silencing is a powerful tool recently developed for salmonid cells, but the approach requires full validation by recovering the functional phenotype. The latter is often carried out through overexpression of the gene of interest using expression vectors that include a strong promoter such as CMV or SV40, commonly reaching non-physiological expression levels (Gibson et al. 2013; Stepanenko and Heng 2017). Stable expression systems have fewer plasmid copies, although they can still generate non-physiological gene expression levels owing to the use of potent constitutive promoters. Inducible expression systems are more appropriate by tightly controlling gene expression enabling functional analysis of a range of physiologically relevant gene expression levels using a single clonal transgenic cell line.