Abstract
Eukaryotes generally display a circadian rhythm as an adaption to the reoccurring day/night cycle. This is particularly true for visual physiology that is directly affected by changing light conditions. Here we investigate the influence of the circadian rhythm on the expression and function of visual transduction cascade regulators in diurnal zebrafish and nocturnal mice. We focused on regulators of shut-off kinetics such as Recoverins, Arrestins, Opsin kinases, and Regulator of G-protein signaling that have direct effects on temporal vision. Transcript as well as protein levels of most analyzed genes show a robust circadian rhythm-dependent regulation, which correlates with changes in photoresponse kinetics. Electroretinography demonstrates that photoresponse recovery in zebrafish is delayed in the evening and accelerated in the morning. Functional rhythmicity persists in continuous darkness, and it is reversed by an inverted light cycle and disrupted by constant light. This is in line with our finding that orthologous gene transcripts from diurnal zebrafish and nocturnal mice are often expressed in an anti-phasic daily rhythm.
Highlights
Circadian rhythms serve as endogenous clocks that molecularly support the daily occurring oscillations of physiology and ensuing behavior (Brown et al, 2019; Cahill, 2002; Frøland Steindal & Whitmore, 2019; Golombek et al, 2014; Idda et al, 2012; Ukai & Ueda, 2010; Vatine et al, 2011)
We show that the expression levels of these important regulators of cone visual transduction decay are modulated by the circadian clock
Eyes from larval [5 day post fertilization) and adult zebrafish that were kept under a normal light cycle (LD 14:10, light on at 8:00 o’clock in the morning), as well as eyes from 5 dpf larvae kept in continuous darkness (DD), were collected every 3 hours over a period of 24 hours and subsequently analyzed
Summary
Circadian rhythms serve as endogenous clocks that molecularly support the daily occurring oscillations of physiology and ensuing behavior (Brown et al, 2019; Cahill, 2002; Frøland Steindal & Whitmore, 2019; Golombek et al, 2014; Idda et al, 2012; Ukai & Ueda, 2010; Vatine et al, 2011). Multiple studies have shown that autonomous circadian clocks exist in other brain regions and in peripheral tissues (Frøland Steindal & Whitmore, 2019; Idda et al, 2012; Vatine et al, 2011) This is true for the retina, which generates its own circadian rhythm (Ko, 2020). In zebrafish this rhythmicity is reflected in a number of circadian adaptations, such as a higher response threshold in the morning (Li & Dowling, 1998), photoreceptor retinomotor movement in constant darkness (Menger et al, 2005) and cone photoreceptor synaptic ribbon disassembly at night (Emran et al, 2010). We show that the expression levels of these important regulators of cone visual transduction decay are modulated by the circadian clock These periodic fluctuations are reflected in oscillating protein levels that correlate with the rhythmicity in visual physiology and behavior observed in zebrafish. The periodicity was opposite to zebrafish, fitting 104 the nocturnal lifestyle of mice
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