Exposure to fluorescent light triggers down regulation of genes involved with mitotic progression in Xiphophorus skin

Abstract

We report RNA-Seq results from skin of X. maculatus Jp 163 B after exposure to various doses of “cool white” fluorescent light (FL). We show that FL exposure incites a genetic transcriptional response in skin nearly as great as observed for UVB exposure; however, the gene sets modulated due to exposure to the two light sources are quite different. Known light responsive genes involved in maintaining circadian cycling (e.g., clock, cry2a, cry1b, per1b, per2, per3, arntl1a, etc.) exhibited expected shifts in transcriptional expression upon FL exposure. Exposure to FL also resulted in down-regulated transcription of many genes involved with cell cycle progression (e.g., cdc20, cdc45, cdca7b, plk1, cdk1, ccnb-3, cdca7a, etc.) and chromosome segregation (e.g., cenpe, cenpf, cenpi, cenpk, cenpo, cenpp, and cenpu; cep70; knstrm, kntc, mcm2, mcm5; smc2, etc.). In addition, several DNA replication and recombination repair genes (e.g., pola1, pole, rec52, rad54l, rpa1, parpbp, etc.) exhibit reduced expression in FL exposed X. maculatus skin. Some genes down modulated by FL are known to be associated with DNA repair and human diseases (e.g., atm2, brip1, fanc1, fancl, xrcc4, etc.). The overall suppression of genes involved with mitotic progression in the skin of adult fish is consistent with entry into the light phase of the circadian cycle. Current efforts are aimed at determining specific wavelengths that may lead to differential expression among the many genes affected by fluorescent light exposure.

Molecular genetic response to varied wavelengths of light in Xiphophorus maculatus skin

“…The genetic effects observed within the 500–550 nm exposure suggest production of a cell based stress response that includes cytoskeletal remodeling and possible apoptosis. In a recent report of differential gene expression, Xiphophorus skin after exposure to “cool white” fluorescent light, a robust suppression of genes involved in cell cycle progression was noted in Walter et al, 2015. A cellular stress response indicated in this region may contribute to the suppression of the cell cycle as was observed for fluorescent light, but clearly cell cycle suppression observed with fluorescent light is due to exposure of more than one 50 nm region (Walter et al, 2015).…”

“…In a recent report of differential gene expression, Xiphophorus skin after exposure to “cool white” fluorescent light, a robust suppression of genes involved in cell cycle progression was noted in Walter et al, 2015. A cellular stress response indicated in this region may contribute to the suppression of the cell cycle as was observed for fluorescent light, but clearly cell cycle suppression observed with fluorescent light is due to exposure of more than one 50 nm region (Walter et al, 2015). Based on results presented herein, the genes involved in this response may be reacting to large fractions of radiance in longer wavelengths around 500 nm and above emitted by standard fluorescent lights.…”

“…Modulation of genes involved with maintaining circadian rhythm that are well documented to be light responsive (Whitmore et al, 2000; Cermakian et al, 2002; Reppert and Weaver, 2002) were examined to test whether the dose of light exposure (10 kJ/m 2 ) at the various wavelength regions mimicked what had been previously observed in Xiphophorus skin (Walter et al, 2014; Yang et al, 2014; Walter et al, 2015). Six differentially expressed circadian genes were identified that met the statistical cut off (± 2-fold cut-off, p -adj ≤ 0.05) in at least one of the six 50 nm wavelength regions tested ( per2 , per1b , per3 , arntl1a [also called bmal1] , clock, and bhlhe40 ; Figure 2).…”

“…The expression pattern of circadian pathway related genes is consistent with previous reports (350–400 nm; clock , arntl1a , per2 , etc., and 500–550 nm; per1b , nr1d2b , arntl2 , etc. ; Yang et al, 2014; Walter et al, 2015). …”

“…metabolism, cytoskeletal, and detoxification) have been documented in mammalian systems (Albrecht et al, 1997; Akhtar et al, 2002). In addition, recent studies have shown gene expression in fish skin to be light responsive (Walter et al, 2014; Boswell et al, 2015, Walter et al, 2015). However, these previous reports dealt exclusively with ultraviolet wavelengths, or more recently, with broad-spectrum fluorescent lights.…”