Establishment and characterisation of single cell-derived embryonic stem cell lines from the gilthead seabream, Sparus aurata

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.

Daily rhythms of locomotor activity and transcript levels of non-visual opsins in the brain of the blind Mexican cavefish (Astyanax mexicanus)

Most organisms possess endogenous circadian clocks that synchronise their physiology and behaviour with environmental cycles, with the light-dark (LD) cycle being the most potent synchronising signal. Consequently, it can be hypothesised that animals that have evolved in the dark, as in caves or deep sea, may no longer possess a functional light-entrained biological clock. In this research, the blind cavefish Astyanax mexicanus was selected as a model organism to investigate the potential effects of daily light conditions on the circadian timekeeping mechanisms. First, we focused on describing behavioural photic entrainment and the presence of a circadian endogenous rhythmicity by recording locomotor activity rhythms under different lighting regimes: LD 12:12, after a 6-h shift of LD, constant darkness (DD), and constant dim light (LLdim). Secondly, we aimed at characterising the mechanisms of photodetection by analysing the daily rhythms of expression of selected non-visual extraocular opsins (exo-rhod, opn3, rgra, rgrb, tmt1a and tmt1b) in the brain of this blind species using real-time quantitative PCR. Our results revealed that blind Mexican cavefish activity rhythms were entrained to the LD cycle, with a diurnal activity pattern that persisted in a circadian fashion under constant lighting conditions. Additionally, statistically significant daily variations and/or rhythms were observed in three out of the six non-visual opsin genes analysed (opn3, rgra and tmt1b), all of them displaying nocturnal acrophases. These findings suggest that daily rhythms in extraretinal non-visual opsins may be transducing daily photic cycles and contributing to the entrainment of locomotor activity and other light-synchronised rhythms in blind cavefish species.

Establishment and application of four long-term culture cell lines of the olive flounder Paralichthys olivaceus blastocysts

Four new embryonic cell lines derived from blastocysts of the olive flounder Paralichthys olivaceus, an important commercial marine fish, were established and characterized. They were designated as PoEFCI, PoEFCII, PoEFCIII, and PoEFCIV and were all fibroblastic cells. The cells were cultured in DMEM/F-12 medium supplemented with antibiotics, FBS, and growth factors at temperature of 25 °C and subcultured for >100 passages over 18 months. The origin of the cell lines was confirmed by examining the partial sequences of the cytochrome oxidase c subunit I (COI) gene of the flounder mitochondrial DNA (mtDNA). The four cell lines showed different growth curve patterns. According to the results of gene and protein expression and enzyme activity, the cell lines PoEFCI, PoEFCII, and PoEFC III could be pluripotent. The cells of all four cell lines were also successfully transfected with the green fluorescent protein (GFP) reporter gene, suggesting that they could be used to study gene function in the flounder or other fish. More importantly, PoEFCI-III were sensitive to chromium (Cr) and red sea bream Pagrus major iridovirus (RSIV), so they could be used as a powerful tool for the study of the toxicological investigation of heavy metals and RSIV in fish. Therefore, these cell lines would be useful for biotechnological and toxicological research on marine fish as an in vitro biological system.