Non-specific interactions are sufficient to explain the position of heterochromatic chromocenters and nucleoli in interphase nuclei

The organization of the eukaryote nucleus into functional compartments arises by self-organization both through specific protein–protein and protein–DNA interactions and non-specific interactions that lead to entropic effects, such as e.g. depletion attraction. While many specific interactions have so far been demonstrated, the contributions of non-specific interactions are still unclear. We used coarse-grained molecular dynamics simulations of previously published models for Arabidopsis thaliana chromatin organization to show that non-specific interactions can explain the in vivo localization of nucleoli and chromocenters. Also, we quantitatively demonstrate that chromatin looping contributes to the formation of chromosome territories. Our results are consistent with the previously published Rosette model for Arabidopsis chromatin organization and suggest that chromocenter-associated loops play a role in suppressing chromocenter clustering

Biomineralization in perforate foraminifera

In this paper, we review the current understanding of biomineralization in perforate foraminifera. Ideas on the mechanisms responsible for the flux of Ca2 + and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera. From the 1980s onward, tracer experiments, fluorescent microscopy and high-resolution test geochemical analysis have added to existing calcification models. Despite recent insights, no general consensus on the physiological basis of foraminiferal biomineralization exists. Current models include seawater vacuolization, transmembrane ion transport, involvement of organic matrices and/or pH regulation, although the magnitude of these controls remain to be quantified. Disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and/or lack of a more systematic approach to study (dis)similarities between taxa. In order to understand foraminiferal controls on element incorporation and isotope fractionation, and thereby improve the value of foraminifera as paleoceanographic proxies, it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

Adolescents Who Intend to Change Multiple Health Behaviours Choose Greater Exposure to an Internet-delivered Intervention

Despite a growth of Internet-delivered interventions, exposure rates to such interventions are still low. In total, 35,104 adolescents participated in the E-MOVO project: an Internet-delivered lifestyle intervention aimed at multiple health behaviours. By means of multilevel analyses, we demonstrated the relationship between intention to change behaviour and adolescents' exposure to E-MOVO's functionalities. There was a clustering of intention to change risk taking behaviours in an unhealthy way and energy balance-related behaviours in a healthy way. This should be taken into account with the design of Internet-delivered interventions. AD - Maastricht University, The Netherlands. [email protected]. FAU - Crutzen, Rik AU - Crutzen R FAU - de Nooijer, Jascha AU - de Nooijer J FAU - Candel, Math J J M AU - Candel MJ FAU - de Vries, Nanne K AU - de Vries NK LA - eng PT - Journal Article PL - England TA - J Health Psychol JT - Journal of health psychology JID - 9703616 SB - I

Impact of salinity on element incorporation in two benthic foraminiferal species with contrasting magnesium contents

Accurate reconstructions of seawater salinity could provide valuable constraints for studying past ocean circulation, the hydrological cycle and sea level change. Controlled growth experiments and field studies have shown the potential of foraminiferal Na ∕ Ca as a direct salinity proxy. Incorporation of minor and trace elements in foraminiferal shell carbonate varies, however, greatly between species and hence extrapolating calibrations to other species needs validation by additional (culturing) studies. Salinity is also known to impact other foraminiferal carbonate-based proxies, such as Mg ∕ Ca for temperature and Sr ∕ Ca for sea water carbonate chemistry. Better constraints on the role of salinity on these proxies will therefore improve their reliability. Using a controlled growth experiment spanning a salinity range of 20 units and analysis of element composition on single chambers using laser ablation-Q-ICP-MS, we show here that Na ∕ Ca correlates positively with salinity in two benthic foraminiferal species (<i>Ammonia tepida</i> and <i>Amphistegina lessonii</i>). The Na ∕ Ca values differ between the two species, with an approximately 2-fold higher Na ∕ Ca in <i>A. lessonii</i> than in <i>A. tepida</i>, coinciding with an offset in their Mg content ( ∼  35 mmol molM<super>−2</super> versus  ∼  2.5 mmol mol−<super>1</super> for <i>A. lessonii</i> and <i>A. tepida</i>, respectively). Despite the offset in average Na ∕ Ca values, the slopes of the Na ∕ Ca–salinity regressions are similar between these two species (0.077 versus 0.064 mmol mol<super>−1</super> change per salinity unit). In addition, Mg ∕ Ca and Sr ∕ Ca are positively correlated with salinity in cultured <i>A. tepida</i> but show no correlation with salinity for <i>A. lessonii</i>. Electron microprobe mapping of incorporated Na and Mg of the cultured specimens shows that within chamber walls of <i>A. lessonii</i>, Na ∕ Ca and Mg ∕ Ca occur in elevated bands in close proximity to the primary organic lining. Between species, Mg banding is relatively similar, even though Mg content is 10 times lower and that variation within the chamber wall is much less pronounced in <i>A. tepida</i>. In addition, Na banding is much less prominent in this species than it is in <i>A. lessonii</i>. Inter-species differences in element banding reported here are hypothesized to be caused by differences in biomineralization controls responsible for element uptake

Anti-cyclonic eddy imprint on calcite geochemistry of several planktonic foraminiferal species in the Mozambique Channel

Hydrographic conditions in the Mozambique Channel are dominated by the passing of large anticyclonic eddies, propagating poleward into the upstream Agulhas area. Further south, these eddies have been found to control the shedding of Agulhas rings into the Atlantic ocean, thereby playing a key role in Indo-Atlantic Ocean exchange. The element composition of several planktonic foraminifera species collected from sediment trap samples, was compared to in situ water column data from the Mozambique Channel. Single-chamber trace element composition of these foraminifera reveals a close coupling with hydrographic changes induced by anticyclonic eddies. Obtained Mg/Ca values for the surface dwelling Globigerinoides ruber as well as the thermocline dwelling Neogloboquadrina dutertrei follow temperature changes and reduced temperature stratification during eddy conditions. At greater depth, Globorotalia scitula and Pulleniatina obliquiloculata record stable temperatures and thus respond to hydrographic changes with a deepening in habitat depth. Furthermore, test Mn/Ca values indicate a close relationship between water column oxygenation and Mn incorporation in these planktonic foraminiferal specie

Salinity control on Na incorporation into calcite tests of the planktonic foraminifera Trilobatus sacculifer – Evidence from culture experiments and surface sediments

The quantitative reconstruction of past seawater salinity has yet to be achieved and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na/Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na/Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na/Ca data, measured on cultured specimens of Trilobatus sacculifer. The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5 °C to 29.5 °C under constant salinity conditions. Foraminiferal Na/Ca ratios positively correlate with seawater salinity (Na/Caforam = 0.97 + 0.115 ⋅ Salinity, R = 0.97, p < 0.005). Temperature on the other hand exhibits no statistically significant relationship with Na/Ca ratios indicating salinity to be the dominant factor controlling Na incorporation. The culturing results are corroborated by measurements on T. sacculifer from Caribbean and Gulf of Guinea surface sediments. In conclusion, planktonic foraminiferal Na/Ca can be applied as a reliable proxy for reconstructing sea surface salinities, albeit species-specific calibrations might be necessary

Comparing stage of change and behavioral intention to understand fruit intake.

We explored if the pre-action Transtheoretical stages of change are indeed discrete stages for fruit intakes. In a longitudinal design, a cohort of 735 adults completed electronic questionnaires assessing fruit intake, stages of change and intention to increase fruit intake at baseline and 35 and 67 days follow-up. A dichotomization of a continuous intention measure ('pseudostages') was compared with precontemplation and contemplation stages. The results showed (i) that pseudostages and stages of change were strongly associated; (ii) that for most respondents, stability and transitions in stages of change resembled transitions in pseudostage, while test-retest reliabilities for both measures were similar and (iii) that pseudostages and the continuous intention measure were stronger predictors of fruit intake than stage of change. We conclude that pre-action stages of change for fruit are not different from a mere categorization of a continuous intention measure

1/f noise in patterned GMR spin valves

abstract onl

Effect of different seawater Mg²⁺ concentrations on calcification in two benthic foraminifers

Magnesium, incorporated in foraminiferal calcite (Mg/CaCC), is used intensively to reconstruct past seawater temperatures but, in addition to temperature, the Mg/CaCC of foraminiferal tests also depends on the ratio of Mg and Ca in seawater (Mg/CaSW). The physiological mechanisms responsible for these proxy relationships are still unknown. This culture study investigates the impact of different seawater [Mg2 +] on calcification in two benthic foraminiferal species precipitating contrasting Mg/CaCC: Ammonia aomoriensis, producing low-Mg calcite and Amphistegina lessonii, producing intermediate-Mg calcite. Foraminiferal growth and test thickness were determined and, Mg/Ca was analyzed using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Results show that at present-day seawater Mg/CaSW of ~ 5, both species have highest growth rates, reflecting their adaptation to modern seawater element concentrations. Test thickness is not significantly affected by different Mg/CaSW. The relationship between Mg/CaSW and Mg/CaCC shows a distinct positive y-axis intercept, possibly reflecting at least two processes involved in foraminiferal biomineralization. The associated Mg partition (DMg) changes non-linearly with increasing Mg/CaSW, hence suggesting that the DMg is best described by an exponential function approaching an asymptot