Abstract
Purpose :
Color vision in vertebrates requires differential expression of multiple specific cone opsins in different cone populations. One model for the regulation of the human long and medium wavelength sensitive (LWS/MWS) opsin tandem array suggests an upstream regulatory region randomly interacts with replicated opsin genes, resulting in the mutually exclusive expression of a specific opsin. However, our prior investigations into the long wavelength sensitive (lws1/lws2) array in zebrafish (sharing a common ancestral LWS gene with the human array) demonstrates that thyroid hormone (TH) and retinoic acid serve as trans regulators of this gene array in larvae/juveniles (Mitchell et al., 2015, PLOS Genetics; Mackin et al., 2019, PNAS). This project utilizes opsin mRNA expression to explore if cone opsin plasticity to TH treatment is retained in adult zebrafish, where the cone distribution has otherwise been considered stable.
Methods :
Adult zebrafish (6-18 months old; both sexes) were treated with NaOH (0.01%, control) or TH (386 nM) for 1 or 5 days. After the treatment period, eyes were harvested and homogenized for mRNA quantification through qRT-PCR. In addition, whole retinas of treated fish underwent hybridization chain reaction (HCR) in situ and then were analyzed by confocal imaging for endogenous expression of lws1 vs lws2 mRNA.
Results :
Exogenous TH treatment in adult zebrafish significantly increased lws1 expression in both 1 and 5 day-treated groups (p<1e-7, 0.01, respectively) while decreasing lws2 expression (p<0.001, 0.001). Other phototransduction-related transcripts (gngt2b, rh2-1) also demonstrated expression changes following TH treatment. Whole retinas showed a substantial expansion of the lws1 domain and restriction of lws2, complementing the qRT-PCR results.
Conclusions :
Consistent with our previous studies of larvae and juveniles, exogenous TH induced a drastic shift from lws2 to lws1 in adult zebrafish. The change in gene expression was observed within as little as 1 day of treatment of TH. Visualization through HCR of lws1/lws2 mRNA revealed a switch from lws2 to lws1 in much of the retina. This rapid shift demonstrates a high degree of plasticity retained in adult zebrafish.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.