Christoph Mayr

Association of P53 and MSH2 with recombinative repair complexes during S-phase

Our previous recombination and biochemical analyses have led to the hypothesis that the tumor suppressor p53 monitors homologous recombination, a function which was previously attributed to the mismatch repair protein MSH2. Here, we show that a certain fraction of p53 is concentrated within discrete nuclear foci of cells synchronized in G1 phase, a pattern which becomes even more pronounced in S phase, especially after γ-ray treatment. p53 foci show some colocalization with MSH2 within distinct foci during G1 phase, while dots formed by BRCA1 display an independent localization pattern. In S phase nuclei, p53 foci almost completely colocalize with MSH2 foci and associate with the recombination surveillance factor BRCA1 in irradiated S phase cells. These p53 and MSH2 foci also show significant overlaps with foci of the recombination enzymes Rad50 and Rad51, which for the first time unveiled recombination-related functions of p53 in replicating cells. During S phase, p53 and MSH2 are maximally active in binding to early recombination intermediates, and coexist within the same nuclear DNA-protein complexes. Our data suggest that p53 is linked similarly to homologous recombination as MSH2 and provide further evidence for the new concept of a dual role of p53 in the regulation of growth and repair.

Comparative analysis of the functional genome architecture of animal and plant cell nuclei.

Many studies have shown that the functional architecture of eukaryotic genomes displays striking similarities in evolutionarily distant organisms. For example, late-replicating and transcriptionally inactive chromatin is associated with the nuclear periphery in organisms as different as budding yeast and man. These findings suggest that eukaryotic genomes are organized in cell nuclei according to conserved principles. In order to investigate this, we examined nuclei of different animal and plant species by comparing replicational pulse-labelling patterns and their topological relationship to markers for heterochromatin and euchromatin. The data show great similarities in the nuclear genome organization of the investigated animal and plant species, supporting the idea that eukaryotic genomes are organized according to conserved principles. There are, however, differences between animals and plants with regard to histone acetylation patterns and the nuclear distribution of late-replicating chromatin.

New insights into paleoenvironmental changes in Laguna Potrok Aike, southern Patagonia, since the Late Pleistocene: The PASADO multiproxy record

A series of long sediment cores was retrieved from Laguna Potrok Aike, Southern Patagonia, within the framework of PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project), an ICDP (International Continental Scientific Drilling Program) lake drilling project. This maar lake, located at 52°S, 70°W in the Province of Santa Cruz (Argentina), in the southernmost continental area of the world, is one of the few permanent lakes in the region, providing a unique continuous paleoclimatic and paleoecological lacustrine record for the last glacial cycle. Previous multiproxy studies of this site have characterized the environmental history of these dry lands in the Patagonian Steppe for the last 16 cal. ka BP. This new series of sediment cores provides a much longer record of climate variability in Southern Patagonia since 51.3 cal. ka BP. Using a multiproxy strategy, a set of samples (mostly from core catcher material) was analyzed for physical properties, rock magnetism, geochemistry, CNS elemental analysis, stable isotopes, pollen and diatoms. This preliminary multiproxy limnogeological interpretation sheds new light on the regional Pleistocene and Holocene environmental history, revealing lake-level variations through time and identifying time windows of interest where higher resolution analyses will be carried out.

Nitrogen and carbon isotope variability in the green-algal lichen Xanthoria parietina and their implications on mycobiont–photobiont interactions

Stable isotope patterns in lichens are known to vary largely, but effects of substrate on carbon and nitrogen stable isotope signatures of lichens were previously not investigated systematically. N and C contents and stable isotope (δ15N, δ13C) patterns have been measured in 92 lichen specimens of Xanthoria parietina from southern Bavaria growing on different substrates (bark and stone). Photobiont and mycobiont were isolated from selected populations and isotopically analyzed. Molecular investigations of the internal transcribed spacer of the nuclear ribosomal DNA (ITS nrDNA) region have been conducted on a subset of the specimens of X. parietina. Phylogenetic analysis showed no correlation between the symbionts X. parietina and Trebouxia decolorans and the substrate, isotope composition, or geographic origin. Instead specimens grown on organic substrate significantly differ in isotope values from those on minerogenic substrate. This study documents that the lichens growing on bark use additional or different N sources than the lichens growing on stone. δ15N variation of X. parietina apparently is controlled predominantly by the mass fraction of the mycobiont and its nitrogen isotope composition. In contrast with mycobionts, photobionts of X. parietina are much more 15N-depleted and show less isotopic variability than mycobionts, probably indicating a mycobiont-independent nitrogen acquisition by uptake of atmospheric ammonia.

Intensified Southern Hemisphere Westerlies regulated atmospheric CO2 during the last deglaciation

The causes for the rise of atmospheric CO 2 during the last deglaciation are complex and remain a matter of controversial scientific discussion. One hypothesis explains this phenomenon with CO 2 release from the deep ocean. A change in atmosphere-ocean interaction induced by a shift or intensification of Southern Hemisphere Westerlies (SHW) could have stimulated this process. Here this hypothesis is tested using oxygen isotope ratios of aquatic cellulose from Patagonian lacustrine sediments as west-wind proxy. Our record indicates maximum SHW strength at 52°S between 13.4 and 11.3 calibrated kyr B.P. This is in agreement with an increase in zonal wind strength extending to the southern mid-latitudes during the Younger Dryas chronozone triggering the final CO 2 increase. Comparison with other Southern Hemisphere records implies southward migration of strengthened SHW at that time, leading to interglacial CO 2 levels and hence terminating the Last Glacial.

Origin and significance of diagenetic concretions in sediments of Laguna Potrok Aike, southern Argentina

Authigenic minerals can form in the water column and sediments of lakes, either abiotically or mediated by biological activity. Such minerals have been used as paleosalinity and paleoproductivity indicators and reflect trophic state and early diagenetic conditions. They are also considered potential indicators of past and perhaps ongoing microbial activity within sediments. Authigenic concretions, including vivianite, were described in late glacial sediments of Laguna Potrok Aike, a maar lake in southernmost Argentina. Occurrence of iron phosphate implies specific phosphorus sorption behavior and a reducing environment, with methane present. Because organic matter content in these sediments was generally low during glacial times, there must have been alternative sources of phosphorus and biogenic methane. Identifying these sources can help define past trophic state of the lake and diagenetic processes in the sediments. We used scanning electron microscopy, phosphorus speciation in bulk sediment, pore water analyses, in situ ATP measurements, microbial cell counts, and measurements of methane content and its carbon isotope composition (δ13CCH4) to identify components of and processes in the sediment. The multiple approaches indicated that volcanic materials in the catchment are important suppliers of iron, sulfur and phosphorus. These elements influence primary productivity and play a role in microbial metabolism during early diagenesis. Authigenic processes led to the formation of pyrite framboids and revealed sulfate reduction. Anaerobic oxidation of methane and shifts in pore water ion concentration indicated microbial influence with depth. This study documents the presence of active microbes within the sediments and their relationship to changing environmental conditions. It also illustrates the substantial role played by microbes in the formation of Laguna Potrok Aike concretions. Thus, authigenic minerals can be used as biosignatures in these late Pleistocene maar sediments.

Isotopic signatures and trophic status of Ramaria

The genus Ramaria is composed of several subgenera that often correspond to specific trophic strategies. Because carbon and nitrogen isotopes can be used to assess fungal trophic status and nitrogen sources, we accordingly carried out an extensive survey of isotopic patterns in archived specimens of Ramaria from Germany and other locations. Isotopic patterns in species generally corresponded to subgeneric affiliations and to the range of different potential substrates, with fungi fruiting on wood and litter (subgenera Asteroramaria and Lentoramaria) much lower in δ15N (≈−3‰) than ectomycorrhizal taxa (≈12‰) (subgenus Ramaria) or taxa fruiting on soil (≈13‰) (subgenus Echinoramaria). Conversely, fungi fruiting on wood and litter were higher in δ13C (−23‰) than those fruiting on soil (≈−27‰), with ectomycorrhizal fungi intermediate (≈−24.5‰). Fungi colonizing mineral soil horizons were about 3‰ enriched in 15N relative to those colonizing both mineral and organic horizons. The high δ15N and low δ13C signatures of taxa fruiting on soil remains unexplained. The high degree of fidelity of isotopic signatures with subgeneric classifications and life history traits suggests that sporocarps are good integrators of patterns of carbon and nitrogen cycling for specific taxa. Archived specimens represent a useful trove of life history information that could be mined without requiring extensive supporting isotopic data from other ecosystem pools.

Isotopic Map of the Inn-Eisack-Adige-Brenner Passage and its Application to Prehistoric Human Cremations

This chapter summarizes the results achieved in an attempt to contribute to bioarchaeological research aiming at the reconstruction of migration and culture transfer in a region of eminent archaeological importance in Europe, namely, the Inn-Eisack-Adige passage via the Brenner Pass in the European Alps. 219 archaeological animal bone samples of three residential species (Bos taurus, Sus scrofa, Cervus elaphus) from 30 archaeological sites covering the transalpine passage have been analysed in terms of δ18Ophosphate, 87Sr/86Sr, 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, 208Pb/207Pb and 206Pb/207Pb, thus generating a multi-isotope fingerprint. All measurement data and the laboratory processing methods are reported in detail. The isotopic map based on the spatial distribution of isotopic signatures in the bone finds is augmented by modern reference samples (water, soil, vegetation) to verify whether the choice of animal skeletal samples was appropriate and to perform a pilot study leading to a predictive model for 87Sr/86Sr isotopic ratios in local bioarchaeological specimens. Univariate statistics for each single isotopic signature and the related maps with the respective spatial distribution are presented.

Linking Oxygen Isotopes of Animal-Bone Phosphate with Altimetry: Results from Archaeological Finds from a Transect in the Alps

Oxygen isotope ratios of organisms are closely linked to the hydrological environment in which they grow up. This is especially the case for mammals. Mammal-bone phosphate is formed at a constant body temperature and, thus, relatively insensitive to temperature-dependent isotope fractionation. The applicability of oxygen isotopes from mammal-bone phosphate for environmental reconstructions is tested here using bones of deer, domestic pig, and domestic cattle from 16 archaeological sites situated along a north–south transect crossing the Alps. Bones of 118 specimens in total were analysed, which covered an age span from the Late Neolithic to the Roman period. The main control on oxygen isotope ratios was site altitude. Significant negative correlations between phosphate isotope values and altitude were registered especially for cattle and pig. Pig bones from one site were deviating from this altitudinal pattern and were excluded from further correlations. Modern equations for translating oxygen isotope ratios of the three species to those of source water were applied. The reconstructed source water isotopic composition showed a similar altitudinal relation as modern Alpine precipitation. As a consequence, our study confirms the utility of oxygen isotope ratios of mammal-bone phosphate for source water and palaeoaltitudinal reconstructions.

Climate Information from Stable Hydrogen and Carbon Isotopes of C3 Plants — Growth Chamber Experiments and Field Observations

This chapter deals with the processes that affect the carbon and hydrogen isotope ratios of plant cellulose. Under natural conditions the influence of a single climate parameter on the isotope composition of tree-rings cannot be evaluated exactly, because of the strong interdependences of the climatic parameters. Results from growth chamber experiments with bean plants (Vicia faba) are presented, in which temperature, relative humidity and irrigation were varied independently from each other. All these parameters were found to be negatively correlated with the δ13C values of stem cellulose. The δD values of stem cellulose were influenced mainly by the humidity of the ambient air and by the isotope signal of the source water. The experimental results may help to explain δD and δ13C values in plant material for the purpose of climate reconstructions. As an example, stable isotope chronologies from tree-rings of spruces (Picea abies) from two different sites in Southern Germany are interpreted in the light of the experimental results.