Photoperiod and Light Spectrum Modulate Daily Rhythms and Expression of Genes Involved in Cell Proliferation, DNA Repair, Apoptosis and Oxidative Stress in a Seabream Embryonic Stem Cell Line.

The use of cell lines as alternative models for environmental physiology studies opens a new window of possibilities and is becoming an increasingly used tool in marine research to fulfil the 3R's rule. In this study, an embryonic monoclonal stem cell line obtained from a marine teleost (gilthead seabream, Sparus aurata) was employed to assess the effects of photoperiod (light/dark cycles vs constant dark) and light spectrum (white, blue, green, blue/green and red lights) on gene expression and rhythms of cellular markers of proliferation, DNA repair, apoptosis and cellular/oxidative stress by RT-qPCR and cosinor analyses. The results obtained revealed the optimal performance of cells under blue light (LDB), with all the genes analysed showing their highest RNA expression levels and most robust daily variations/rhythms in this condition. Under LDB, the mRNA levels of cell proliferation (pcna), DNA repair (cry5), anti-apoptotic (bcl2) and oxidative stress (prdx2) markers peaked at the day-night transition, whereas pro-apoptotic (bax) and cell stress (hsp70) markers showed their highest expression at the night-day transition, evidencing the strong synchronisation of the transcription of key genes involved in the cell cycle in this photoregime. The persistence of significant pcna, cry5, hsp70 and prdx2 rhythms after 3 days in constant darkness reveals the endogenous and circadian nature of these rhythms. Our results highlight the importance of implementing photoperiods with light-dark cycles of blue wavelengths when performing fish cell culture research. These results reinforce and extend our previous studies, confirming the importance of lighting conditions that mimic the natural environment for the proper development of fish embryos and larvae in aquaculture.