An exploratory study on the combined effects of external and internal morphology on load dissipation in primate capitates: its potential for an understanding of the positional and locomotor repertoire of early hominins

This pilot study explored whether the redirection of stress through trabeculae within morphologically constrained capitates provides information about habitual/positional behaviours unavailable from the study of external morphology alone. To assess this possibility, an experimental finite element approach was taken, whereby no attempt was made to reconstruct the actual magnitudes and loading conditions experienced by the capitates in vivo. Rather, this work addressed fundamental biological questions relating to bone plasticity, i.e. internal versus external bone morphology. The capitates of 7 species with different and - in the case of fossils - inferred locomotor behaviours were selected. Virtual models of capitates were created, scaled to the same size and subjected to the same theoretical load. In the first set of analyses, models were assigned the material properties of bone throughout, whereas in the second set, models were assigned 11 different material properties representing the trabecular architecture derived from high-resolution CT. Species with arboreal behaviours consistently redirected loads towards the ulnar aspect of the capitate when trabeculae were introduced, while terrestrial species, and the bipedal Homo, redirected stress towards the radial side. From these preliminary analyses, it is tentatively concluded that Australopithecus anamensis habitually engaged in arboreal behaviours, whereas Australopithecus afarensis did not.     

The contribution of epipelon to total sediment microalgae in a shallow temperate eutrophic loch (Loch Leven, Scotland)

Benthic microalgae are known to perform important ecosystem functions in shallow lakes. As such it is important to understand the environmental variables responsible for regulating community structure, positioning and biomass. We tested the hypothesis that the positioning (across a depth gradient of 2–22 m overlying water depth) and relative biomass (determined using bulk and lens tissue harvested chlorophyll (Chl) a concentrations) of the epipelon community would vary independently with season (12 monthly samples) and across natural gradients of light and habitat disturbance relative to the total benthic algal community (i.e. all viable microalgae in the surface sediments) in a shallow eutrophic loch. Total sediment microalgal Chl a concentrations (TS-Chl; range: 5–874 μg Chl a g⁻¹ dw) were highest in winter and in the deepest site (20 m overlying water depth), apparently as a result of phytoplanktonic settling and sediment focussing processes. Epipelic Chl a concentrations (Epi-Chl; range: <0.10–6.0 μg Chl a g⁻¹ dw) were highest in winter/spring, a period when water clarity was highest and TS-Chl lowest. Principal components analysis highlighted strong associations between Epi-Chl and sites of intermediate depths (2.5–5.5 m) in all seasons except autumn/winter. Autumn/winter represented the season with the highest average wind speeds preceding sampling, during which the highest Epi-Chl concentrations were associated with the deepest sites. Epi-Chl was associated with intermediate light and habitat disturbance during spring/summer and summer/autumn and varied positively with habitat disturbance, only, in autumn/winter and winter/spring. The epipelon community structure also varied with depth; diatoms dominated shallow water sediments, cyanobacteria dominated deep water sediments, and sediments at sites of intermediate depth returned the highest biovolume estimates and the most diverse communities. This study has strengthened the hypothesis that the structure and biomass of benthic microalgal communities in lakes are regulated by habitat disturbance and water clarity, both of which are expected to respond to climate change and eutrophication. The degree to which these structural responses reflect functional performance requires clarification.     

A history of scientific research at Loch Leven,Kinross, Scotland

Loch Leven is a large, shallow lake in lowland Scotland, UK. Scientific research began here almost 200 years ago. Early research characterised the biodiversity and physical characteristics of the loch, providing an important historical background for future research. In the mid-1960s, this ad hoc approach was superseded by a more structured research programme under the umbrella of the International Biological Programme. This was the beginning of the Loch Leven long-term monitoring programme. Today, the results of these studies form one of the longest and most comprehensive limnological datasets for shallow freshwater lakes in the world, comprising more than 500 physical, chemical and biological variables collected at two-weekly intervals. To celebrate the 40th anniversary of the start of the long term monitoring programme, and to highlight the scientific investigations still being conducted at Loch Leven, the NERC Centre for Ecology & Hydrology (CEH) organised a symposium entitled “Loch Leven: 40 years of scientific research” in Kinross, Scotland, UK, on 11 December 2008. This examined the role of long-term monitoring in developing our understanding of the links between pollution, climate change and ecological responses in shallow lakes. This article introduces a series of papers summarising the scientific results presented at this meeting.     

Ctr1 Is an Apical Copper Transporter in Mammalian Intestinal Epithelial Cells in Vivo That Is Controlled at the Level of Protein Stability

Copper is an essential trace element that functions in a diverse array of biochemical processes that include mitochondrial respiration, neurotransmitter biogenesis, connective tissue maturation, and reactive oxygen chemistry. The Ctr1 protein is a high-affinity Cu⁺ importer that is structurally and functionally conserved in yeast, plants, fruit flies, and humans and that, in all of these organisms, is localized to the plasma membrane and intracellular vesicles. Although intestinal epithelial cell-specific deletion of Ctr1 in mice demonstrated a critical role for Ctr1 in dietary copper absorption, some controversy exists over the localization of Ctr1 in intestinal epithelial cells in vivo. In this work, we assess the localization of Ctr1 in intestinal epithelial cells through two independent mechanisms. Using immunohistochemistry, we demonstrate that Ctr1 localizes to the apical membrane in intestinal epithelial cells of the mouse, rat, and pig. Moreover, biotinylation of intestinal luminal proteins from mice fed a control or a copper-deficient diet showed elevated levels of both total and apical membrane Ctr1 protein in response to transient dietary copper limitation. Experiments in cultured HEK293T cells demonstrated that alterations in the levels of the glycosylated form of Ctr1 in response to copper availability were a time-dependent, copper-specific posttranslational response. Taken together, these results demonstrate apical localization of Ctr1 in intestinal epithelia across three mammalian species and suggest that increased Ctr1 apical localization in response to dietary copper limitation may represent an adaptive response to homeostatically modulate Ctr1 availability at the site of intestinal copper absorption.     

A single zinc ion is sufficient for an active Trypanosoma brucei tRNA editing deaminase

Editing of adenosine (A) to inosine (I) at the first anticodon position in tRNA is catalyzed by adenosine deaminases acting on tRNA (ADATs). This essential reaction in bacteria and eukarya permits a single tRNA to decode multiple codons. Bacterial ADATa is a homodimer with two bound essential Zn(2+). The ADATa crystal structure revealed residues important for substrate binding and catalysis; however, such high resolution structural information is not available for eukaryotic tRNA deaminases. Despite significant sequence similarity among deaminases, we continue to uncover unexpected functional differences between Trypanosoma brucei ADAT2/3 (TbADAT2/3) and its bacterial counterpart. Previously, we demonstrated that TbADAT2/3 is unique in catalyzing two different deamination reactions. Here we show by kinetic analyses and inductively coupled plasma emission spectrometry that wild type TbADAT2/3 coordinates two Zn(2+) per heterodimer, but unlike any other tRNA deaminase, mutation of one of the key Zn(2+)-coordinating cysteines in TbADAT2 yields a functional enzyme with a single-bound zinc. These data suggest that, at least, TbADAT3 may play a role in catalysis via direct coordination of the catalytic Zn(2+). These observations raise the possibility of an unusual Zn(2+) coordination interface with important implications for the function and evolution of editing deaminases.     

Further studies on the cell-free synthesis of procollagen-collagen by chick embryo polysomes

Free and membrane bound polysomes were prepared from 8-day-old chick embryos. Both polysome preparations were equally active in protein synthesis but procollagen-collagen synthesis was carried out exclusively by the membrane bound polysomes. The collagenous product was analyzed by DEAE-cellulose chromatography and after hydroxylation with peptidyl proline hydroxylase had a hydroxyproline/proline ratio of 0.77. This suggests that the collagenous product synthesized by the membrane bound polysomes is procollagen.     

The long-term (1979–2005) effects of the North Atlantic Oscillation on wind-induced wave mixing in Loch Leven (Scotland)

We report on long-term covariation (1979–2005) between indices of the North Atlantic Oscillation (NAO) and wind speed and direction in Loch Leven. The effects of the observed variations in wind speed and direction were combined to produce modelled wave-mixed depths (Zc). Positive correlations were observed between seasonal and annual wind speeds and westerly frequency and indices of the NAO that are in line with general perception: positive NAO was correlated with stronger, more westerly winds and these correlations were strongest in winter and spring. Correlations between NAO and estimates of Zc were strongest in the most westerly exposed site in spring (r ² = 0.701; Zc_spring versus spring NAO index). On average, over a 25-year period Zc was deeper in spring and shallower in summer. Major anomalies from the 25-year seasonal means were observed in 1982, 1979, and 1991. Annual average Zc was low in the late 1970s and early 1980s (shallowest average annual Zc of 1.0 m (1984)), high in the late 1980s and early 1990s (deepest average annual Zc of 1.9 m (1990)) and moderate in recent years (up to 2005). This study has major implications for our understanding of potential climate change drivers and the related responses of shallow lake ecosystems, including alterations to littoral habitat quality and benthic–pelagic coupling.