Synthesis of bis-spermine dimers that are potent polyamine transport inhibitors.

A series of novel spermine dimer analogues was synthesized and assessed for their ability to inhibit spermidine transport into MDA-MB-231 breast carcinoma cells. Two spermine molecules were tethered via their N(1) primary amines with naphthalenedisulfonic acid, adamantanedicarboxylic acid and a series of aliphatic dicarboxylic acids. The linked spermine analogues were potent polyamine transport inhibitors and inhibited cell growth cytostatically in combination with a polyamine synthesis inhibitor. Variation in the linker length did not alter polyamine transport inhibition. The amount of charge on the molecule may influence the molecular interaction with the transporter since the most potent spermidine transport inhibitors contained 5-6 positive charges.     

Selection for phenotypic plasticity in Rana sylvatica tadpoles

The hypothesis that phenotypic plasticity is an adaptation to environmental variation rests on the two assumptions that plasticity improves the performance of individuals that possess it, and that it evolved in response to selection imposed in heterogeneous environments. The first assumption has been upheld by studies showing the beneficial nature of plasticity. The second assumption is difficult to test since it requires knowing about selection acting in the past. However, it can be tested in its general form by asking whether natural selection currently acts to maintain phenotypic plasticity. We adopted this approach in a study of plastic morphological traits in larvae of the wood frog, Rana sybatica. First we reared tadpoles in artificial ponds for 18 days, in either the presence or absence of Anax dragonfly larvae (confined within cages to prevent them from killing the tadpoles). These conditioning treatments produced dramatic differences in size and shape: tadpoles from ponds with predators were smaller and had relatively short bodies and deep tail fins. We estimated selection by Anax on the two kinds of tadpoles by testing for non-random mortality in overnight predation trials. Dragonflies imposed strong selection by preferentially killing individuals with relatively shallow and short tail fins, and narrow tail muscles. The same traits that exhibited the strongest plasticity were under the strongest selection, except that tail muscle width exhibited no plasticity but experienced strong increasing selection. A laboratory competition experiment, testing for selection in the absence of predators, showed that tadpoles with deep tail fins grew relatively slowly. In the cattle tanks, where there were also no free predators, the predator-induced phenotype survived more poorly and developed slowly, but this cost was apparently not associated with particular morphological traits. These results indicate that selection is currently promoting morphological plasticity in R. sylvatica, and support the hypothesis that plasticity represents an adaptation to variable predator environments.     

Progression of human bone marrow stromal cells into both osteogenic and adipogenic lineages is differentially regulated by structural conformation of collagen I matrix via distinct signaling pathways

Adult human bone marrow stromal cells (BMSCs) containing or consisting of mesenchymal stem cells (MSCs) are an important source in tissue homeostasis and repair. Although many processes involved in their differentiation into diverse lineages have been deciphered, substantial inroads remain to be gained to synthesize a complete regulatory picture. The present study suggests that structural conformation of extracellular collagen I, the major organic matrix component in musculoskeletal tissues, plays, along with differentiation stimuli, a decisive role in the selection of differentiation lineage. It introduces a novel concept which proposes that structural transition of collagen I matrix regulates cell differentiation through distinct signaling pathways specific for the structural state of the matrix. Thus, on native collagen I matrix inefficient adipogenesis is p38-independent, whereas on its denatured counterpart, an efficient adipogenesis is primarily regulated by p38 kinase. Inversely, osteogenic differentiation occurs efficiently on native, but not on denatured collagen I matrix, with a low commencement threshold on the former and a substantially higher one on the latter. Osteogenesis on collagen I matrices in both structural conformations is fully dependent on ERK. However, whereas on native collagen I matrix osteogenic differentiation is Hsp90-dependent, on denatured collagen I matrix it is Hsp90-independent. The matrix conformation-mediated regulation appears to be one of the mechanisms determining differentiation lineage of BMSCs. It allows a novel interpretation of the bone remodeling cycle, explains the marked physiological aging-related adipogenic shift in musculoskeletal tissues, and can be a principal contributor to adipogenic shift seen in a number of clinical disorders.     

A PCR-based linkage map of Agrostis stolonifera and identification of QTL markers for dollar spot resistance

Creeping bentgrass (Agrostis stolonifera L.) is the most widely utilized cool-season turf species for intensively managed sports playing surfaces, including bowling greens and golf course putting greens, tees, and fairways. One of the biggest disease problems affecting creeping bentgrass is dollar spot disease caused by Sclerotinia homoeocarpa F.T. Bennett. Relative to traditional food crops, little attention has been paid to applying molecular technology to traditional creeping bentgrass breeding programs. The objective of this study was to develop a PCR-based linkage map of creeping bentgrass and identify quantitative trait loci (QTLs) associated with dollar spot resistance. Mapping populations segregating for dollar spot resistance were created, phenotyped for disease resistance, and genotyped for simple sequence repeat, conserved intron scanning primer, intron length polymorphism, and amplified fragment length polymorphism markers. As expected, 14 linkage groups (LGs) were detected for each parental map, covering a total of 1,424 and 1,374 cM for the 7418-3 and the L93-10 parental maps, respectively. A total of eight QTL regions (23 markers) for dollar spot resistance were observed for three isolates (Crenshaw, PRG, and UMass1) in our creeping bentgrass mapping populations. LGs 1, 4, and 5 contained at least two overlapping QTL regions to different isolates, indicating that these regions may play a significant role in dollar spot resistance. Identification of QTLs associated with disease resistance will help to facilitate marker-assisted selection in traditional creeping bentgrass breeding programs.     

Linking recruitment to trophic factors: revisiting the Beverton--Holt recruitment model from a life history and multispecies perspective

The Beverton--Holt recruitment model can be derived from arguments about evolution of life history traits related to foraging and predation risk, along with spatially localized and temporarily competitive relationships in the habitats where juvenile fish forage and face predation risk while foraging. This derivation explicitly represents two key biotic factors, food supply (I) and predator abundance (R), which appear as a risk ratio (R/I) that facilitates modelling of changes in trophic circumstances and analysis of historical data. The same general recruitment relationship is expected whether the juvenile life history is simple or involves a complex sequence of stanzas; in the complex case, the Beverton--Holt parameters represent weighted averages or integrals of risk ratios over the stanzas. The relationship should also apply in settings where there is complex, mesoscale variation in habitat and predation risk, provided that animals sense this variation and move about so as to achieve similar survival at all mesoscale rearing sites. The model predicts that changes in food and predation risk can be amplified violently in settings where juvenile survival rate is low, producing large changes in recruitment rates over time.     

The Millennial model: in search of measurable pools and transformations for modeling soil carbon in the new century

Soil organic carbon (SOC) can be defined by measurable chemical and physical pools, such as mineral-associated carbon, carbon physically entrapped in aggregates, dissolved carbon, and fragments of plant detritus. Yet, most soil models use conceptual rather than measurable SOC pools. What would the traditional pool-based soil model look like if it were built today, reflecting the latest understanding of biological, chemical, and physical transformations in soils? We propose a conceptual model—the Millennial model—that defines pools as measurable entities. First, we discuss relevant pool definitions conceptually and in terms of the measurements that can be used to quantify pool size, formation, and destabilization. Then, we develop a numerical model following the Millennial model conceptual framework to evaluate against the Century model, a widely-used standard for estimating SOC stocks across space and through time. The Millennial model predicts qualitatively similar changes in total SOC in response to single factor perturbations when compared to Century, but different responses to multiple factor perturbations. We review important conceptual and behavioral differences between the Millennial and Century modeling approaches, and the field and lab measurements needed to constrain parameter values. We propose the Millennial model as a simple but comprehensive framework to model SOC pools and guide measurements for further model development.     

Introduced and native herbivores have different effects on plant composition in low productivity ecosystems

Questions

Understanding how livestock grazing alters plant composition in low productivity environments is critical to managing livestock sustainably alongside native and introduced wild herbivore populations. We asked four questions: (1) does recent livestock and rabbit grazing reduce some plant attributes more strongly than others; (2) does grazing by introduced herbivores (i.e. livestock and rabbits) affect plants more strongly than native herbivores (i.e. kangaroos); (3) do the effects of recent livestock grazing differ from the legacy effects of livestock grazing; and (4) does the probability of occurrence of exotic plants increase with increasing net primary productivity (NPP)?

Location

South‐eastern Australia.

Methods

We measured the recent grazing activity of co‐occurring livestock (cattle, sheep, goats), rabbits and kangaroos by counting faecal pellets; historic grazing activity by measuring livestock tracks; and derived NPP from satellite imagery. We used a hierarchical GLMM to simultaneously model the presence or absence (i.e. probability of occurrence) of all plant species as a function of their attributes (growth form, lifespan and origin) to assess their average response to recent grazing, historic grazing and productivity in a broad‐scale regional study.

Results

Recent and historic livestock grazing, rabbit grazing and increasing NPP reduced the average probability of occurrence of plant species, although responses varied among plant attributes. Both recent and historic livestock grazing strongly reduced the average probability of occurrence of native species, and forbs and geophytes, but differed in their relative effects on other growth forms. Recent livestock grazing, rabbit grazing and NPP had similar effects, strongly reducing native species and forbs, geophytes, shrubs and sub‐shrubs. The overall effects of recent kangaroo grazing were relatively weak, with no clear trends for any given plant attribute.

Conclusion

Our results highlight the complex nature of grazing by introduced herbivores compared with native herbivores on different plant attributes. Land managers need to be aware that domestic European livestock, rabbits and other free‐ranging introduced livestock such as goats have detrimental impacts on native plant communities. Our results also show that kangaroo grazing has a relatively benign effect on plant occurrence.