Comparison of UV-B tolerance between wild and hatchery-reared juveniles of red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli)

The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0?W/m²) for 4?h. Survival rate was measured every 2?h for a period of 24?h (red sea bream) or 48?h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0?% 24?h after exposure at the 1.1 and 1.8?W/m² levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8?W/m². Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species.     

p53-independent apoptosis in UV-irradiated mouse skin: possible inhibition by 50 Hz magnetic fields

Our recent results suggest that 50 Hz magnetic fields (MF) enhance ultraviolet (UV)-induced tumorigenesis in mouse skin. The aim of the present experiment was to study suppression of apoptosis as a possible mechanism for MF effects on skin tumorigenesis. Another aim was to test the importance of a UV and MF exposure schedule, particularly the role of MF exposure prior to UV irradiation. Female mice were exposed to a UV dose of 2 human MED and to 100 microT MF of 50 Hz, using the following exposure schedules: group 1 sham MF 24 h, UV 1 h, sham MF 24 h; group 2 sham MF 24 h, UV 1 h, MF 24 h; group 3 MF 24 h, UV 1 h, MF 24 h. Lamps emitting simulated solar radiation (SSR) were used for UV irradiation. Skin samples were analysed for apoptosis, expression of the p53 gene, activity of the enzyme ornithine decarboxylase (ODC) and polyamine concentrations. A significantly (p = 0.017) lower number of apoptotic cells was measured in group 2 compared to group 1. A similar but not statistically significant (p = 0.064) decrease was also detected in group 3. No p53 expression was detected in any sample. The levels of ODC and putrescine did not differ significantly between the UV-only and UV and MF-exposed groups. Spermidine and spermine levels were significantly (p = 0.014 and 0.014, respectively) lower in group 3 than in group 1, but no decrease was observed in group 2. Our findings suggest that SSR induces p53-independent apoptosis in mouse skin and that the apoptotic response may be inhibited by exposure to MF. The exposure schedule did not alter the MF effect. The results do not support a causal role for polyamines in MF effects on apoptosis.     

Keratinocytes exposed to ultraviolet radiation reveal three down-regulated genes with potential function in differentiation and cell cycle control

The incidence of skin cancer is increasing in epidemic proportion. Although solar UV radiation is known to be the major risk factor, much information is lacking about the molecular mechanisms leading to skin cancer. To gain a deeper insight into these mechanisms, we have examined cells of a human keratinocyte cell line (HaCat) after exposure to 0.16 minimal erythema doses of UVB radiation. This dose led to an S-phase delay that was reversible 22 h postirradiation. To examine gene expression 10 h after UV irradiation, a nonradioactive differential display was employed. Three genes were identified as being down-regulated significantly. The first encodes for topoisomerase-IIbeta-binding protein 1 (expression level 5% 6 h after irradiation). This protein is associated with human topoisomerase IIbeta and appears to be necessary for DNA replication during the onset of S phase. The second gene product has previously been reported to be involved in differentiation and is therefore known as differentiation-dependent A4 protein (28% 8 h after irradiation). The third gene is XPO1 (also known as CRM1) (5% 8 h after irradiation), whose protein is involved in nuclear export of mRNA molecules. Differential expression of these genes after UV irradiation has not been reported. Because of their potential involvement in cell cycle control and differentiation, these proteins could be important for understanding the reaction of keratinocytes after exposure to UV radiation.     

Estimations of the human 'vitamin D' UV exposure in the USA.

Human exposure to sunlight promotes the formation of pre-vitamin D in the skin. Low or marginal levels of vitamin D has been linked to a wide range of human health outcomes, including the development of various types of cancer. However, few data exist on the actual exposure to human due to vitamin D producing ultraviolet radiation. Most studies of human disease and vitamin D have linked latitude and location of residence to expected exposure form the available ambient UV radiation. Human UV exposure for the development of vitamin D depends on a variety of factors such as time spent outdoors, percent available skin, skin type, UV protective devices used and distribution of UV over the human form. In this paper, we investigate how latitude impacts not only on the amount of UV available for vitamin D synthesis, but also the distribution of UV over the human form.     

Differential expression of 10 sweetpotato peroxidases in response to sulfur dioxide, ozone, and ultraviolet radiation

Secretory class III plant peroxidase (POD, EC 1.11.1.7) is believed to function in diverse physiological processes, including responses to various environmental stresses. To understand the function of each POD in terms of air pollutants and UV radiation, changes in POD activity and expression of 10 POD genes isolated from cell cultures of sweetpotato (Ipomoea batatas) were investigated in the leaves of sweetpotato after treatment with sulfur dioxide (SO(2) 500ppb, 8h/day for 5 days), ozone (O(3) 200ppb, 8h/day for 6 days), and ultraviolet radiation (UV-B 0.6mWm(-2) for 24h, UV-C 0.16mWm(-2) for 24h). All treatments significantly reduced the PSII photosynthetic efficiency (F(v)/F(m)). POD-specific activities (units/mg protein) were increased in leaves treated with SO(2) and O(3) by 5.2- and 7.1-fold, respectively, compared to control leaves. UV-B and UV-C also increased POD activities by 3.0- and 2.4-fold, respectively. As determined by RT-PCR analysis, 10 POD genes showed differential expression patterns upon treatment with air pollutants and UV radiation. Among the POD genes, swpa1, swpa2, and swpa4 were strongly induced following each of the treatments. Interestingly, basic POD genes (swpb1, swpb2, and swpb3) were highly expressed following SO(2) treatment only, whereas neutral swpn1 was highly induced following O(3) treatment only. These results indicated that some specific POD isoenzymes might be specifically involved in the defense mechanism against oxidative stress induced by air pollutants and UV radiation in sweetpotato plants.     

Activation of mammalian gene expression by the UV component of sunlight – from models to reality

Ultraviolet radiation activates the expression of a wide variety of genes, by pathways which differ between the short non-solar ultraviolet C (UVC) wavelengths, which are strongly absorbed by nucleic acids, and the long solar ultraviolet A (UVA, 320–380 nm) wavelengths, which generate active oxygen intermediates. Intermediate solar ultraviolet (UV) wavelengths in the UVB (290–320 nm) range also contain an oxidative component, but more closely resemble UVC in their gene activating properties. Short wavelength UV, in common with other extracellular stimuli including growth factors, activates signal transduction events that involve both stress- and mitogen-activated protein kinase cascades. The extrapolation of the complex modulation of gene expression that ensues to the consequences of natural UV exposure requires careful attention to the details of doses and wavelength employed in the model experiments. Nevertheless, there is evidence that UVB irrradiation of skin can activate the expression of proteins including immunomodulating cytokines, ornithine decarboxylase and, to a limited extent, nuclear oncogene products, as well as lead to stabilisation of p53. Non-cytotoxic doses of UVA radiation also lead to the strong activation of several genes which would be expected to have functional relevance in vivo.     

RecA Expression in Response to Solar UVR in the Marine Bacterium Vibrio natriegens

Solar ultraviolet radiation may produce daily stress on marine and estuarine communities as cells are damaged and repair that damage. Reduction in the earth's stratospheric ozone layer has increased awareness of the potential effects that ultraviolet radiation may have in the environment, including how marine bacteria respond to changes in solar radiation. We examined the use of the bacterial RecA protein as an indicator of the potential of bacteria to repair DNA damage caused by solar UV irradiation using the marine bacterium Vibrio natriegens as a model. RecA is universally present in bacteria and is a regulator protein for the so-called Dark Repair Systems, which include excision repair, postreplication recombinational repair, and mutagenic or SOS repair. Solar UVB and UVA both reduced V. natriegens viability in seawater microcosms. After exposure to unfiltered solar radiation or radiation in which UVB was blocked, survival dropped below 1%, whereas visible light from which UVA and UVB had been filtered had no effect on survival. Using a RecA-specific antibody for detection, RecA protein was induced by solar radiation in a diel pattern in marine microcosms conducted in the Gulf of Mexico. Peak induction was observed at dusk each day. Although RecA expression was correlated with the formation of UVB-induced cyclobutyl pyrimidine dimers, longer wavelength UVA radiation also induced recA gene expression. Our results demonstrate that RecA-regulated, light-independent repair is an important component in the ability of marine bacteria to survive exposure to solar ultraviolet radiation and that RecA expression is a useful monitor of bacterial repair after exposure to solar UVR.     

Photooxidation and antioxidant responses in the earthworm Amynthas gracilis exposed to environmental levels of ultraviolet B radiation

Ultraviolet (UV) radiation leads to photooxidation in various organisms. Our previous study demonstrated that ultraviolet B (UV-B) radiation is lethal for particular species of earthworms, but the mechanisms responsible for the lethality are unclear. In our current study, we investigated that ultraviolet light causes photooxidative damage and reduces antioxidant responses in the earthworm Amynthas gracilis. Intact earthworms and skin/muscle tissue extracts were exposed to UV-B radiation for in vivo and in vitro studies. Both in vitro and in vivo results showed that the products of photooxidative damage, MDA and H₂O₂, increased after UV-B exposure. Glutathione peroxidase (GPx) and catalase were inhibited immediately after exposure to high doses (3000 J/m²) of UV-B radiation in vivo. Catalase activity was increased following a low UV-B dose (500 J/m²) in vivo, but decreased in response to all dosage levels in vitro. These data indicate that a relationship exists between UV-B induced damage and photooxidation and also that catalase and GPx act as important antioxidants to prevent photooxidation. According to these data, A. gracilis exhibits high sensitivity to environmental levels of UV-B. Therefore, A. gracilis represents a sensitive and cost-effective model organism for investigations of UV-radiation damage and environmental UV stress.