Grk7 but not Grk1 undergoes cAMP-dependent phosphorylation in zebrafish cone photoreceptors and mediates cone photoresponse recovery to elevated cAMP

Avermectin induces photoreceptor functional impairment and color vision deficits in zebrafish (Danio rerio)

The effects of avermectin on the visual function of nontarget organisms, particularly aquatic organisms, require further evaluation. Avermectin can come into direct contact with the eyes of nontarget organisms through air or water. However, few studies have investigated the safety of avermectin in the eyes of nontarget organisms. Therefore, it is important to assess its safety in the eyes of nontarget organisms. The results demonstrate that avermectin induces ocular morphological abnormalities, retinal structural damage, and decreased locomotor behavior in zebrafish larvae. Further analyses indicate that avermectin-induced ocular toxicity in zebrafish larvae is associated with the thyroid hormone and retinoic acid signaling pathways. The evaluation of the effect of avermectin on the visual function of adult zebrafish reveals that avermectin induces changes in the sensitivity of adult zebrafish to different light wavelengths and colors. Male adult zebrafish showed greater variation, suggesting possible sex differences. These results indicate that avermectin induces ocular developmental damage in zebrafish larvae and visual behavioral abnormalities in adult zebrafish.

tet2 and tet3 regulate cell fate specification and differentiation events during retinal development

Tet family methylcytosine dioxygenases recognize and oxidize 5-methyl-cytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Previous work demonstrated the requirement for Tet and 5hmC during zebrafish retinogenesis. tet2-/-;tet3-/- mutants possessed defects in the formation of differentiated retinal neurons, but the mechanisms underlying these defects are unknown. Here, we leveraged scRNAseq technologies to better understand cell type-specific deficits and molecular signatures underlying the tet2-/-;tet3-/- retinal phenotype. Our results identified defects in tet2-/-;tet3-/- retinae that included delayed specification of several retinal cell types, reduced maturity across late-stage cones, expansions of immature subpopulations of horizontal and bipolar cells, and altered biases of bipolar cell subtype fates at late differentiation stages. Together, these data highlight the critical role that tet2 and tet3 play as regulators of cell fate specification and terminal differentiation events during retinal development.

tet2 and tet3 regulate cell fate specification and differentiation events during retinal development

Tet enzymes are epigenetic modifiers that impact gene expression via 5mC to 5hmC oxidation. Previous work demonstrated the requirement for Tet and 5hmC during zebrafish retinogenesis. tet2 -/- ;tet3 -/- mutants possessed defects in the formation of differentiated retinal neurons, but the mechanisms underlying these defects are unknown. Here, we leveraged scRNAseq technologies to better understand cell type-specific deficits and molecular signatures underlying the tet2 -/- ;tet3 -/- retinal phenotype. Our results identified defects in the tet2 -/- ;tet3 -/- retinae that included delayed specification of several retinal cell types, reduced maturity across late-stage cones, expansions of immature subpopulations of horizontal and bipolar cells, and altered biases of bipolar cell subtype fates at late differentiation stages. Together, these data highlight the critical role that tet2 and tet3 play as regulators of cell fate specification and terminal differentiation events during retinal development.

Phototoxicity avoidance is a potential therapeutic approach for retinal dystrophy caused by EYS dysfunction

Inherited retinal dystrophies (IRDs) are progressive diseases leading to vision loss. Mutation in the eyes shut homolog (EYS) gene is one of the most frequent causes of IRD. However, the mechanism of photoreceptor cell degeneration by mutant EYS has not been fully elucidated. Here, we generated retinal organoids from induced pluripotent stem cells (iPSCs) derived from patients with EYS-associated retinal dystrophy (EYS-RD). In photoreceptor cells of RD organoids, both EYS and G protein-coupled receptor kinase 7 (GRK7), one of the proteins handling phototoxicity, were not in the outer segment, where they are physiologically present. Furthermore, photoreceptor cells in RD organoids were vulnerable to light stimuli, and especially to blue light. Mislocalization of GRK7, which was also observed in eys-knockout zebrafish, was reversed by delivering control EYS into photoreceptor cells of RD organoids. These findings suggest that avoiding phototoxicity would be a potential therapeutic approach for EYS-RD.

Grk1 Missense Mutations in Type II Oguchi Disease: A Literature Review

Oguchi disease is a rare form of congenital stationary night blindness resulting from arrestin-1 (SAG) or rhodopsin kinase (GRK1) loss-of-function mutations. Unlike other congenital nyctalopias, patients with Oguchi disease can reach the dark-adapted state, albeit only after several hours of sustained darkness exposure. The mechanism underlying rhodopsin kinase dysfunction in Oguchi disease remains understudied. Previous research utilized the Grk1 knockout mice to reveal its role in phototransduction, the process that transduces light into neuronal signals in rod and cone photoreceptors. By studying Grk1 missense mutations via a knock-in approach, a more complete picture of the Oguchi disease mechanism involving GRK1 may be readily harvested. We summarize here the current knowledge on the Type II Oguchi disease with Grk1 missense mutations by focusing on the interaction of GRK1 with other proteins, and how these interactions influence dark adaptation. We call for more detailed analyses of GRK1 missense mutations in animal models, particularly V380D and L157P, to reveal novel disease mechanisms to gain further insight onto GRK1's action and function.

Effect of GRK4 on renal gastrin receptor regulation in hypertension

OBJECTIVE

To investigate whether GRK4 regulates the phosphorylation and function of renal CCKBR.

METHODS

GRK4 A142V transgenic mice were used as an animal model of enhanced GRK4 activity, and siRNA was used to silence the GRK4 gene to investigate the regulatory effect of GRK4 on CCKBR phosphorylation and function. Finally, the co-localization and co-connection of GRK4 and CCKBR in RPT cells were observed by laser confocal microscopy and immunoprecipitation to explore the mechanism of GRK4 regulating CCKBR.

RESULTS

Gastrin infusion significantly increased urinary flow and sodium excretion rates in GRK4 WT mice (P < .05). GRK4 siRNA did not affect CCKBR protein expression in WKY RPT cells and SHR RPT cells, but remarkably reduced CCKBR phosphorylation in WKY and SHR RPT cells (P < .05). The inhibitory effect of gastrin on Na+-K+ -ATPase activity in WKY RPT cells was further enhanced by the reduction of GRK4 expression (P < .05), while GRK4 siRNA restored the inhibitory effect of gastrin on Na+-K+ -ATPase activity in SHR RPT cells. Laser confocal and Co-immunoprecipitation results showed that GRK4 and CCKBR co-localized in cultured RPT cells' cytoplasm.

CONCLUSION

GRK4 participates in the development of hypertension by regulating the phosphorylation of renal CCKBR leading to impaired CCKBR function and water and sodium retention. Knockdown of GRK4 restored the function of CCKBR. The enhanced co-connection between GRK4 and CCKBR may be an important reason for the hyperphosphorylation of GRK4 and CCKBR involved in the pathogenesis of hypertension.