Thyroid hormone receptor beta mutations alter photoreceptor development and function inDanio rerio(zebrafish)

Abstract

We investigate a splice variant of thrb isolated in the retina, trβ2, identifying functional changes in larval and adult mutant zebrafish lacking trβ2. We constructed two CRISPR mutant zebrafish with mutations located in the N-terminus region. The first is a 6BP+1 insertion deletion frameshift resulting in a truncated protein. The second is a 3BP in frame deletion with intact binding domains. ERG recordings showed that the 6BP+1 mutants did not respond to red wavelengths of light while the 3BP mutants did respond. 6BP+1 mutants lacked optomotor and optokinetic responses to red/black and green/black contrasts. Adult 6BP+1 mutants exhibit a loss of red-cone contribution to the ERG, and an increase in green and UV contributions. Anatomical markers show loss of red-cones in the 6BP+1 mutant but increase in blue, green, and UV cone density. Our results confirm trβ2's role in retinal cone development. Author SummaryThere are four cone photoreceptors responsible for color vision in zebrafish: red, green, blue, and UV. The thyroid hormone receptor trβ2 is localized in the vertebrate retina. We know that it is necessary for the development of long-wavelength-sensitive cones (red), but here we investigate the functional alterations that accompany a loss of trβ2. Our work contributes to the ongoing investigations of retinal development and the involvement of thyroid hormone receptors. Confirming previous morphological findings, we see that the fish become red colorblind when trβ2 is knocked out, but the contributions of the other three cone types shift in response. Our work highlights the plasticity of the retinal circuit as we see changes in opsin peaks and cone sensitivity, increases in contributions of UV cones, and an attempt at a mosaic pattern in the adult retina all in the absence of trβ2 and red cones. We now have an increased understanding of mechanisms underlying retinal development ResultsCRISPR mutations are located in the N-terminus of trβ2. The two splice variants of the thrb gene, trβ1 and trβ2 differ only in the first exon [14]. To target trβ2, we designed gRNA targeting exon1 of trβ2 and injected into one-cell-stage eggs of tg(trβ2:tdTomato). We isolated

Foxq2 determines blue cone identity in zebrafish

“…1H) manifested a massive reduction of both lws1 and lws2 expression and a concomitant increase in sws1 expression in the larval eyes ( Fig. 1I) as reported in previous studies (16,(26)(27)(28). We noticed that thrb ja27 mutant exhibited a moderate but significant increase in sws2 gene expression ( Fig.…”

Circuit mechanisms for colour vision in zebrafish

“…In striking agreement, the spectral Review sensitivity function of adult zebrafish optokinetic behaviour 98 is essentially an in-between of the larva's broad red-cone tuning and the narrower red-opponent fraction of the green-cones (G opp. , Figure 5H; see also Deveau et al 99 ). In fact, such a sharper-than-opsin long-wavelength tuning of optokinetic behaviour occurs in diverse vertebrates, including in goldfish 100,101 but also in frogs 102 and turtles 101 , suggesting that this is a widespread organisational principle.…”

Ecological adaptation in Atlantic herring is associated with large shifts in allele frequencies at hundreds of loci

“…Another interesting locus is THRB ( thyroid hormone-receptor beta ) on Chr19 encoding a medically important nuclear receptor. Mutations in THRB cause generalized thyroid hormone resistance in human ( Ferrara et al, 2012 ) and a recent CRISPR study in zebrafish revealed its function in photoreceptor development ( Deveau et al, 2019 ). At the herring THRB locus, all populations from high salinity conditions (34–35 PSU) are fixed for an Atlantic haplotype whereas, with a few exceptions, a ‘Baltic’ haplotype, which must have been introgressed from the sister species Pacific herring, dominates in all populations from the Baltic Sea, the transition zone and Norwegian fjords ( Figure 5—figure supplement 2 ).…”