Is there direct photoentrainment in the goldfish liver? Wavelength-dependent regulation of clock genes and investigation of the opsin 7 family.

Abstract

Widespread direct photoentrainment in zebrafish peripheral tissues is linked to diverse non-visual opsins. To explore whether this broadly distributed photosensitivity is specific to zebrafish or is a general teleost feature, we investigated hepatic photosynchronization in goldfish. First, we focused on the opsin 7 family (OPN7, a key peripheral novel opsin in zebrafish), investigating its presence in the goldfish liver. Subsequently, we studied whether light can directly entrain the goldfish liver and retina clocks. Silico analysis revealed seven OPN7 paralogs from four gene families, suggesting expansion through whole-genome and tandem duplications. The paralogs of families OPN7a, OPN7b, and OPN7d were mainly localized in neural tissues, while OPN7c paralogs were more abundant in peripheral tissues-including the liver-suggesting divergent roles. Light (independently of the wavelength employed) directly induced the per2a clock gene in the retina both in vivo and in vitro, confirming expected photoentrainment. However, in the liver, photoinduction of per1a and cry1a only occurred in vivo, not in vitro. These results suggest an indirect light-entrainment mechanism of the goldfish hepatic clock, possibly mediated by other oscillators or photosensitive organs. Our findings challenge the assumption of widespread direct photosensitivity in the peripheral tissues of teleosts. Further research is needed to understand the role of tissue-specific photoentrainment and non-visual opsins in diverse teleost species.