Effect of 1alpha,25(OH)2-vitamin D3 on TNF alpha-mediated apoptosis of human primary osteoblast-like cells in vitro.

1alpha,25(OH)2-vitamin D3 is a hormone which potentially stimulates bone cell growth and differentiation. TNFalpha is one possible inductor for apoptosis; apoptosis being an important regulatoring factor for bone modelling and remodelling. We examined the influence of physiological levels (0.1 nM) 1alpha,25(OH)2-vitamin D3 on TNFalpha-mediated apoptosis in human osteoblast-like cells. These human cells were obtained from bone fragments obtained during orthopedic operations on patients without systemic bone disease. Treatment with 1alpha,25(OH)2-vitamin D3 for 8 weeks resulted in a significant reduction (30%) of viable cell number compared to untreated cells. Incubation with TNFalpha (100 ng/ml for 4 hours) only had limited effects on the rate of apoptosis in control cells. After pretreatment with 1alpha,25(OH)2-vitamin D3, induction of apoptosis increased up to 10% in human osteoblast-like cells. In parallel to the induction of apoptosis, 1alpha,25(OH)2-vitamin D3 stimulated osteocalcin and alkaline phosphatase as markers of mature osteoblasts. Our data suggest that 1alpha,25(OH)2-vitamin D3 has a stimulatory effect on TNFalpha-induced apoptosis in human osteoblast-like cells as a result of 1alpha,25(OH)2-vitamin D3-induced cell differentiation.     

Regulation of the expression of histone H3.3 by differential polyadenylation.

Previously we have shown that the 3' untranslated regions (UTRs) of the replacement histone genes H3.3.A and H3.3B of Drosophila melanogaster differ in their nucleotide sequences and have different polyadenylation sites. To understand their functional relevance, which might explain the presence and evolutionary conservation of 2 different H3.3 genes, green fluorescent protein (GFP) constructs with different 3' UTR sections were studied by the expression of GFP as a marker protein. Here we show that the polyadenylation signals modify the cell-specific translation of the histone replacement variants in testes and ovaries. The H3.3A gene may be required to provide postmeiotic histone H3.3 in the male germ line in transition to chromatin packaging in sperm.     

The aPKC/Par3/Par6 Polarity Complex and Membrane Order Are Functionally Interdependent in Epithelia During Vertebrate Organogenesis

The differential distribution of lipids between apical and basolateral membranes is necessary for many epithelial cell functions, but how this characteristic membrane organization is integrated within the polarity network during ductal organ development is poorly understood. Here we quantified membrane order in the gut, kidney and liver ductal epithelia in zebrafish larvae at 3–11 days post fertilization (dpf) with Laurdan 2‐photon microscopy. We then applied a combination of Laurdan imaging, antisense knock‐down and analysis of polarity markers to understand the relationship between membrane order and apical‐basal polarity. We found a reciprocal relationship between membrane order and the cell polarity network. Reducing membrane condensation by exogenously added oxysterol or depletion of cholesterol reduced apical targeting of the polarity protein, aPKC. Conversely, using morpholino knock down in zebrafish, we found that membrane order was dependent upon the Crb3 and Par3 polarity protein expression in ductal epithelia. Hence our data suggest that the biophysical property of membrane lipid packing is a regulatory element in apical basal polarity.     

Telomere length reflects reproductive effort indicated by corticosterone levels in a long‐lived seabird

Telomere length (TL) is a candidate biomarker of ageing and phenotypic quality, but little is known of the (physiological) causes of TL variation. We previously showed that individual common terns Sterna hirundo with high reproductive success had short telomeres independent of age, and this pattern was particularly strong in the longer telomeres of the within‐individual TL distribution. To test whether this relation can be attributed to effects of reproductive effort, we investigated baseline corticosterone in relation to reproductive success (number of fledglings) and TL. In this context, we assume that variation in baseline corticosterone can be interpreted as index of energy expenditure and allostatic load. Males with higher corticosterone levels during incubation, compared between and within individuals, achieved higher reproductive success and had shorter telomeres. The effect on telomeres was more pronounced in corticosterone measured later in incubation and in the longer telomeres of the within‐individual TL distribution. Female corticosterone level during incubation was neither related to reproductive success nor to TL. That we observed these effects only in males mirrors different parental roles during reproduction in the common tern, where males do most of the chick provisioning. The negative association between reproductive success and TL suggests individual differences in reproductive effort as reflected in, or mediated by, baseline corticosterone. We see this result as a promising step towards unravelling the physiological causes of variation in TL and the costs of reproduction.     

Spatiotemporal choreography of chromosome and megaplasmids in the Sinorhizobium meliloti cell cycle

A considerable share of bacterial species maintains multipartite genomes. Precise coordination of genome replication and segregation with cell growth and division is vital for proliferation of these bacteria. The α‐proteobacterium Sinorhizobium meliloti possesses a tripartite genome composed of one chromosome and the megaplasmids pSymA and pSymB. Here, we investigated the spatiotemporal pattern of segregation of these S. meliloti replicons at single cell level. Duplication of chromosomal and megaplasmid origins of replication occurred spatially and temporally separated, and only once per cell cycle. Tracking of FROS (fluorescent repressor operator system)‐labelled origins revealed a strict temporal order of segregation events commencing with the chromosome followed by pSymA and then by pSymB. The repA2B2C2 region derived from pSymA was sufficient to confer the spatiotemporal behaviour of this megaplasmid to a small plasmid. Altering activity of the ubiquitous prokaryotic replication initiator DnaA, either positively or negatively, resulted in an increase in replication initiation events or G1 arrest of the chromosome only. This suggests that interference with DnaA activity does not affect replication initiation control of the megaplasmids.     

Patterns and drivers of phytodiversity in steppe grasslands of Central Podolia (Ukraine)

We asked: (i) Which environmental factors determine the level of α-diversity at several scales and β-diversity in steppic grasslands? (ii) How do the effects of environmental factors on α- and β-diversity vary between the different taxonomic groups (vascular plants, bryophytes, lichens)? We sampled nested-plot series ranging from 0.0001 to 100 m² and additional 10-m² plots, covering different vegetation types and management regimes in steppes and semi-natural dry grasslands of Central Podolia (Ukraine). We recorded all terricolous taxa and used topographic, soil, land-use and climatic variables as predictors. Richness-environment relationships at different scales and across taxonomic groups were assessed with multimodel inference. We also fitted power-law species-area relationships, using the exponent (z value) as a measure of β-diversity. In general, the richness values in the study region were intermediate compared to those known from similar grasslands throughout the Palaearctic, but for 1 cm² we found seven species of vascular plants, a new world record. Heat index was the most important factor for vascular plants and bryophytes (negative relation), while lichen diversity depended mainly on stone and rock cover (positive). The explanatory power of climate-related variables increased with increasing grain size, while anthropogenic burning was the most important factor for richness patterns at the finest grain sizes (positive effect). The z values showed more variation at the finest grain sizes, but no significant differences in their mean between scales. The results highlight the importance of integrating scale into ecological analyses and nature conservation assessments in order to understand and manage biological diversity in steppe ecosystems.     

How does size and isolation affect patches of steppe-like vegetation on slumping hills in Transylvania,Romania?

The region of Southern Transylvania in Romania contains large expanses of species-rich grassland and mixed farmland. Within these landscapes, clusters of small, steep-sided slumping hills support mosaics of herbaceous vegetation caused by the heterogeneity in temperature and water supply and maintained by mowing or grazing. These are of conservation interest not only for the high species density, but also the relict steppe-like vegetation types especially found on their south-facing slopes. Usually surrounded by more intensively used mesic grassland, these hills can be considered patches of species-rich grassland vegetation. We therefore surveyed the vascular plants in 10 m² plots on the south- and north-facing slopes of 50 hills in 12 clusters in order to investigate the influence of their size and isolation on the species richness and composition of the vegetation. We found that larger hills had higher plot-scale species richness, a greater proportion of competitive species and a lower proportion of species of steppe-like vegetation, but only on their south-facing slopes where the conditions are more extreme. Both large and small hills should be considered as important habitats and potential sources of propagules for plant communities in the surrounding areas.     

Hydroxyproline O‐arabinosyltransferase mutants oppositely alter tip growth in Arabidopsis thaliana and Physcomitrella patens

Hydroxyproline O‐arabinosyltransferases (HPATs) are members of a small, deeply conserved family of plant‐specific glycosyltransferases that add arabinose sugars to diverse proteins including cell wall‐associated extensins and small signaling peptides. Recent genetic studies in flowering plants suggest that different HPAT homologs have been co‐opted to function in diverse species‐specific developmental contexts. However, nothing is known about the roles of HPATs in basal plants. We show that complete loss of HPAT function in Arabidopsis thaliana and the moss Physcomitrella patens results in a shared defect in gametophytic tip cell growth. Arabidopsis hpat1/2/3 triple knockout mutants suffer from a strong male sterility defect as a consequence of pollen tubes that fail to fully elongate following pollination. Knocking out the two HPAT genes of Physcomitrella results in larger multicellular filamentous networks due to increased elongation of protonemal tip cells. Physcomitrella hpat mutants lack cell‐wall associated hydroxyproline arabinosides and can be rescued with exogenous cellulose, while global expression profiling shows that cell wall‐associated genes are severely misexpressed, implicating a defect in cell wall formation during tip growth. Our findings point to a major role for HPATs in influencing cell elongation during tip growth in plants.     

Scale- and taxon-dependent patterns of plant diversity in steppes of Khakassia,South Siberia (Russia)

The drivers of plant richness at fine spatial scales in steppe ecosystems are still not sufficiently understood. Our main research questions were: (i) How rich in plant species are the natural steppes of Southern Siberia compared to natural and semi-natural grasslands in other regions of the Palaearctic? (ii) What are the main environmental drivers of the diversity patterns in these steppes? (iii) What are the diversity–environment relationships and do they vary between spatial scales and among different taxonomic groups? We sampled the steppe vegetation (vascular plants, bryophytes and lichens) in Khakassia (Russia) with 39 nested-plot series (0.0001–100-m² plot size) and 54 additional 10-m² quadrats across the regional range of steppe types and measured various environmental variables. We measured β-diversity using z-values of power-law species–area relationships. GLM analyses were performed to assess the importance of environmental variables as predictors of species richness and z-value. Khakassian steppes showed both high α- and β-diversity. We found significant scale dependence for the z-values, which had their highest values at small spatial scales and then decreased exponentially. Total species richness was controlled predominantly by heat load index, mean annual precipitation, humus content and soil skeleton content. The positive role of soil pH was evident only for vascular plant species richness. Similar to other studies, we found that the importance of environmental factors strongly differed among taxonomic groups and across spatial scales, thus highlighting the need to study more than one taxon and more than one plot size to get a reliable picture.