Zebrafish Circadian Clock Entrainment and the Importance of Broad Spectral Light Sensitivity

Abstract

One of the key defining features of an endogenous circadian clock is that it can be entrained or set to local time. Though a number of cues can perform this role, light is the predominant environmental signal that acts to entrain circadian pacemakers in most species. For the past 20 years, a great deal of work has been performed on the light input pathway in mammals and the role of intrinsically photosensitive retinal ganglion cells (ipRGCs)/melanopsin in detecting and sending light information to the suprachiasmatic nucleus (SCN). In teleost fishes, reptiles and birds, the biology of light sensitivity is more complicated as cells and tissues can be directly light responsive. Non-visual light signalling was described many years ago in the context of seasonal, photoperiodic responses in birds and lizards. In the case of teleosts, in particular the zebrafish model system, not only do peripheral tissues have a circadian pacemaker, but possess clear, direct light sensitivity. A surprisingly wide number of opsin photopigments have been described within these tissues, which may underpin this fundamental ability to respond to light, though no specific functional link for any given opsin yet exists. In this study, we show that zebrafish cells show wide spectral sensitivities, as well as express a number of opsin photopigments-several of which are under direct clock control. Furthermore, we also show that light outside the visual range, both ultraviolet and infrared light, can induce clock genes in zebrafish cells. These same wavelengths can phase shift the clock, except infrared light, which generates no shift even though genes such as per2 and cry1a are induced.

Consequences of directly- and indirectly-experienced heat stress in a mutagenic environment

“…Next, zebrafish embryos were immediately transferred (within 1 min) to the UVA setup which consisted of a 15-min exposure at 27°C in a ‘sandwich’ system of PCR handle stations (365 nm UVA, 4W UVA output, Spectroline ENF-240C/FE) comprised of one bottom-up (direct contact against the bottom of the Petri dish) and one on top-down (11 mm away from embryos due to the height of the petri dish) UVA sources. The UVA setup was placed in the laboratory under both visible light from bulbs and natural sunlight which also excite DNA repair enzymes such as photolyases (Steindal and Whitmore, 2020). The UV irradiance could not be measured in the laboratory.…”

Introduction to biological rhythms: A brief history of chronobiology and its relevance to parasite immunology

“…Light is the predominant synchronizing signal for most organisms, and some cells can directly entrain to light (e.g. in zebrafish 45 ). However, in the majority of animals, cellular clocks are entrained via central nervous system (CNS) circuits and output pathways from a central pacemaker in the brain.…”

“…Cca-circadian clock associated, Ccg-clock-controlled genes, Clk-clock, Cry-cryptochrome, EE-evening element, Frh-FRQ interacting RNA helicase, Frq-frequency, Lhy-late elongated hypocotyl, Per-period, Prr-pseudoresponse regulator, RVE-reveille, Tim-timeless, Toc-timing of CAB expression, Vri-vrille, WC-white collar most organisms, and some cells can directly entrain to light (e.g. in zebrafish 45 ). However, in the majority of animals, cellular clocks are entrained via central nervous system (CNS) circuits and output pathways from a central pacemaker in the brain.…”

Biochemistry and physiology of zebrafish photoreceptors

“…Many, but not all of them, are expressed in the photoreceptor layer. Their functions in photoreceptors are largely unknown, but a role in circadian light entrainment is discussed [ 56 , 174 , 26 ].…”