Hyaluronan (HA), a major component of the cutaneous extracellular-matrix, is involved in tissue repair. Human skin is exposed to and damaged by UVB-irradiation. Here, we investigate the regulation of HA metabolism in human skin during acute UVB-induced inflammation. Expression of HA synthesizing (HAS) and degrading enzymes hyaluronidase (HYAL) as evaluated by quantitative reverse transcribed PCR in response to UVB differed when fibroblasts and HaCaT-keratinocytes, representative cell types in dermis and epidermis, respectively, were compared. Both demonstrated temporally different expression patterns of these genes 3- and 24-hours post-irradiation. This resulted 24-hours post-irradiation in an increase in HAS gene expression in both fibroblasts and HaCaT-keratinocytes, and an increase in HYAL expression only in fibroblasts. HA-production as analyzed by the HA content of conditioned medium was reduced in HaCaT and fibroblast cultures 3-hours post-irradiation, whereas HA increased in HaCaT-cultures 24-hours post-irradiation but remained suppressed in fibroblasts-cultures. Consistently, immunohistochemical staining for HA in human skin 24-hours post-irradiation demonstrated an increased epidermal HA, but a decrease in the dermal compartment. Moreover, analysis of the HA content of dermal microdialysis-fluid revealed increased accumulation of HA degradation products 24-hours post-irradiation. These data demonstrate that there is a complex temporal and spatial regulation of HA-metabolism in skin in response to UVB irradiation.

-X-ray photoelectron spectroscopy (XPS) has been used to investigate the interaction of copper(II)-containing aerated aqueous solution (pH 4-10) with pyrite (FeS,) surfaces and its influence on subsequent ethyl xanthate adsorp tion from solution. Evidence is provided that Cu(I1) ions can be adsorbed independent of pH, changing their oxidation state to Cu(1). This is attributed to a new CUS surface species. In addition, Cu(I1) can be stabilized as a complex hydroxy species on pyrite at pH 2 6. Time-dependent adsorption studies were carried out to elucidate the influence of pH on the copper adsorption rate, considering also the different copper oxidation states. A fast saturation of the sulphide surface with Cu(1) is observed at pH 5, whereas the Cu(1) uptake starts only slowly at pH 8 and pH 10. Prolonged conditioning in alkaline solution results in a Precipitation of Cu(I2) hydroxy species. Simultaneously, the amount of adsorbed Cu(1) increases until the same Cu(1) level is reached as in acidic media. After subsequent immersion in ethyl xanthate solution of pH 6-9, both Cu(1) and Cu(I1) ions adsorbed on pyrite are found to form Cu(1) ethyl xanthate in accordance with previously published infrared spectroscopic and microflotation results.

Author contributions: DKD, RD, KR and RCV designed the study. RCV collected and analyzed the lifespan data. SV performed the Wolbachia screen and the genotyping analysis.RCV and DKD wrote the manuscript. All authors edited the manuscript. Acknowledgements:We are grateful to members of the Dowling and Sgró labs for their support in the lab work associated with this project, and four anonymous reviewers for comments on a previous version of the manuscript.

Drosophila melanogaster as a cosmopolitan species has successfully adapted to a wide range of different environments. Variation in temperature is one important environmental factor that influences the distribution of species in nature. In particular for insects, which are mostly ectotherms, ambient temperature plays a major role in their ability to colonize new habitats. Chromatinbased gene regulation is known to be sensitive to temperature. Ambient temperature leads to changes in the activation of genes regulated in this manner. One such regulatory system is the Polycomb group (PcG) whose target genes are more expressed at lower temperatures than at higher ones. Therefore, a greater range in ambient temperature in temperate environments may lead to greater variability (plasticity) in the expression of these genes. This might have detrimental effects, such that positive selection acts to lower the degree of the expression plasticity. We provide evidence for this process in a genomic region that harbors two PcG-regulated genes, polyhomeotic proximal (ph-p) and CG3835. We found a signature of positive selection in this gene region in European populations of D. melanogaster and investigated the region by means of reporter gene assays. The target of selection is located in the intergenic fragment between the two genes. It overlaps with the promoters of both genes and an experimentally validated Polycomb response element (PRE). This fragment harbors five sequence variants that are highly differentiated between European and African populations. The African alleles confer a temperature-induced plasticity in gene expression, which is typical for PcG-mediated gene regulation, whereas thermosensitivity is reduced for the European alleles.

There is a growing interest in investigating the relationship between genes with signatures of natural selection and genes identified in QTL mapping studies using combined population and quantitative genetics approaches. We dissected an X-linked interval of 6.2 Mb, which contains two QTL underlying variation in chill coma recovery time (CCRT) in Drosophila melanogaster from temperate (European) and tropical (African) regions. This resulted in two relatively small regions of 131 kb and 124 kb. The latter one co-localizes with a very strong selective sweep in the European population. We examined the genes within and near the sweep region individually using gene expression analysis and P-element insertion lines. Of the genes overlapping with the sweep, none appears to be related to CCRT. However, we have identified a new candidate gene of CCRT, brinker, which is located just outside the sweep region and is inducible by cold stress. We discuss these results in light of recent population genetics theories on quantitative traits.