1. Introduction

Xiphophorus maculatus (platyfish), Danio rerio (zebrafish), and Oryzias latipes (medaka), that are utilized as experimental models in biomedical research [ Xiphophorus skin [ Over three billion years of evolution occurred exclusively under sunlight. Thus, all spectral wavelengths were represented, and each organism had the opportunity to adaptively pair genetic responses with discrete regions and/or intensities of solar spectrum wavelengths inherent to their environmental niche. In contrast to the solar spectrum, fluorescent light (FL) has only been used for ≈60 years. The FL light spectrum is comprised of a much narrower range of wavelengths and exhibits sharp peaks and valleys of intensity for select wavelengths, when compared to the broad and consistent solar spectrum. We recently characterized changes in gene expression after FL exposure to be both robust and conserved in the skin of three divergent small fish species;(platyfish),(zebrafish), and(medaka), that are utilized as experimental models in biomedical research [ 1 2 ]. In addition, we have reported that exposure to select wavelengths of light may serve to induce, or suppress, specific genetic pathways inskin [ 3 ]. These studies established that exposure to one wavelength may activate genes in specific biochemical pathways, while exposure to a different wavelength of light can be used to suppress the same pathway. These studies support the concept that, over evolutionary time, each wavelength in the solar spectrum may have been conscripted for regulation of specific genetic pathways. If so, exposure to the full complement of solar wavelengths may be necessary to produce the agonistic/antagonistic genetic signaling needed for proper interaction of an organism with its environment.

5,6,7,8,9,10, Use of broad-spectrum artificial lighting has been shown to have the potential to produce adverse effects on human health, including depression, disturbed sleep–wake cycles, obesity, altered body temperature, and altered circadian rhythms [ 4 11 ]. However, little research has been conducted to determine genetic consequences, if any, from use of common artificial light sources. We have reported that exposure to FL in the skin of both zebrafish and medaka modulates gene expression patterns consistent with activation of inflammation and cellular immune responses [ 1 ]. However, in addition to the conserved primary response, each fish also shows other light-induced gene expression alterations that are unique to each species. Such species-specific genetic responses to the same FL source may reflect genetic fine-tuning of the organismal light response, according to evolution within unique environmental niches. This may suggest ocular photoreception and the genetic perception response to light are overlapping but separate processes.

X. maculatus exposed to ultraviolet light (UVB, 311 nm, [ Additional evidence for differences in the genetic perception of light have also been observed in male and femaleexposed to ultraviolet light (UVB, 311 nm, [ 12 ]). When highly inbred siblings (i.e., over 100 generations) are exposed to the same UVB light source, most of the induced gene expression responses are shared by both sexes. However, males and females also show opposite UVB induced modulation of gene sets in important pathways, such as synaptic development, cell differentiation, wound healing, glucose metabolism, and free radical scavenging. Thus, gender differences within a species may affect the genetic response to light exposure. While these studies document some differences in the specific gene sets modulated after light exposure, it is important to note that for skin, the primary consequence of FL exposure for all fish species examined appears to a be well-conserved induction of the inflammation and immune response.

Previous studies of the genetic response to FL, UVB, or specific wavelengths of light have involved only the skin of several fish models. Potential transcriptional effects within internal organs after light exposure of intact animals has not been reported. In addition, fish skin is a genetically dynamic organ compared to the skin of mammals. Thus, it is of interest to determine whether the conserved fish gene expression responses to FL exposure would extend to the skin of mammals.

Herein we report results of comparative studies using RNA-Seq to assess modulation of transcriptional profiles following exposure to 4100 K “cool-white” FL for two commonly utilized fish models (zebrafish and medaka) and a mammalian model (the hairless mouse). FL induced responses in gene expression were measured in skin, a direct light receiving organ, and two internal organs, the brain and liver. In spite of considerable evolutionary divergence (i.e., ≈450 My) and drastically different lifestyles (i.e., diurnal fish and nocturnal mice), a highly conserved primary genetic response to FL exposure was observed. In skin, brain, and liver of all three animals, FL exposure led to modulation of the acute phase response pathway, with concurrent promotion of inflammation and immune responses. The only major difference in the primary response to FL was observed in the mouse liver, that modulated the same pathways as the fish livers, but in the opposite direction compared to the fishes (i.e., suppression in mouse liver, induction in fish livers). These findings support the concept that light-induced genetic circuitry is highly conserved and deeply embedded in the vertebrate genome.