Single-cell profiling of photoreceptor cells in adult zebrafish

Vertebrate vision is mediated by two kinds of photoreceptors, rods and cones, responsible for dim- and bright-light vision, respectively. Gene expression differences among cone subtypes remain poorly understood compared with rods. We generated single-cell transcriptome data using a droplet-based approach to reveal the extent of gene expression diversity among adult zebrafish photoreceptor subtypes. Populations of photoreceptor cells were enriched by using the transgenic zebrafish lines, Tg(rho:EGFP)ja2Tg and Tg(gnat2:EGFP)ja23Tg, which express GFP in rods and all cone subtypes, respectively. By analyzing the single-cell transcriptomes, we found that in addition to the four canonical zebrafish cone types (ultraviolet, blue, green and red), there exist subpopulations of green and red cones in the ventral retina that express red-shifted opsin paralogs (opn1mw4 and opn1lw1). This work lays a foundation for future studies aimed at understanding how molecular differences among cone subtypes affect photoreceptor function. GFP-positive cells collected from two transgenic zebrafish, Tg(rho:EGFP)ja2Tg and Tg(gnat2:EGFP)ja23Tg were combined into one sample. A small percentage of GFP-negative cells was also included in the sample.