Development of a screening system for agents that modulate taste receptor expression with the CRISPR-Cas9 system in medaka

Taste recognition mediated by taste receptors is critical for the survival of animals in nature and is an important determinant of nutritional status and quality of life in humans. However, many factors including aging, diabetes, zinc deficiency, infection with influenza or cold viruses, and chemotherapy can trigger dysgeusia, for which a standard treatment has not been established. We here established an engineered strain of medaka (Oryzias latipes) that expresses green fluorescent protein (GFP) from the endogenous taste 1 receptor 3 (T1R3) gene locus with the use of the CRISPR-Cas9 system. This T1R3-GFP knock-in (KI) strain allows direct visualization of expression from this locus by monitoring of GFP fluorescence. The pattern of GFP expression in the T1R3-GFP KI fish thus mimicked that of endogenous T1R3 gene expression. Furthermore, exposure of T1R3-GFP KI medaka to water containing monosodium glutamate or the anticancer agent 5-fluorouracil resulted in an increase or decrease, respectively, in GFP fluorescence intensity, effects that also recapitulated those on T1R3 mRNA abundance. Finally, screening for agents that affect GFP fluorescence intensity in T1R3-GFP KI medaka identified tryptophan as an amino acid that increases T1R3 gene expression. The establishment of this screening system for taste receptor expression in medaka provides a new tool for the development of potential therapeutic agents for dysgeusia.