Abstract
Purpose :
Color vision in vertebrates requires differential expression of multiple specific cone opsins in different cone populations. In humans, the long and middle wavelength-sensing opsins (LWS/MWS) are encoded in a tandemly replicated array. The process by which human LWS and MWS opsins are differentially regulated remains largely unknown. Our prior investigations into the tandemly replicated 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 determine whether 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 5 days, 1 day, or 12 hours. After the treatment period, eyes were harvested and homogenized for mRNA quantification through qRT-PCR. In addition, whole retinas of treated fish underwent multiplex 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 in as little as 12 hours.
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 12 hours of treatment with TH. Visualization 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 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.