Ocean acidification may increase calcification rates, but at a cost

Ocean acidification is the lowering of pH in the oceans as a result of increasing uptake of atmospheric carbon dioxide. Carbon dioxide is entering the oceans at a greater rate than ever before, reducing the ocean's natural buffering capacity and lowering pH. Previous work on the biological consequences of ocean acidification has suggested that calcification and metabolic processes are compromised in acidified seawater. By contrast, here we show, using the ophiuroid brittlestar Amphiura filiformis as a model calcifying organism, that some organisms can increase the rates of many of their biological processes (in this case, metabolism and the ability to calcify to compensate for increased seawater acidity). However, this upregulation of metabolism and calcification, potentially ameliorating some of the effects of increased acidity comes at a substantial cost (muscle wastage) and is therefore unlikely to be sustainable in the long term.     

Plasma membrane residence of hyaluronan synthase is coupled to its enzymatic activity

Hyaluronan is a multifunctional glycosaminoglycan up to 10(7) Da molecular mass produced by the integral membrane glycosyltransferase, hyaluronan synthase (HAS). When expressed in keratinocytes, N-terminally tagged green fluorescent protein-HAS2 and -HAS3 isoenzymes were found to travel through endoplasmic reticulum (ER), Golgi, plasma membrane, and endocytic vesicles. A distinct enrichment of plasma membrane HAS was found in cell protrusions. The total turnover time of HAS3 was 4-5 h as judged by the green fluorescent protein signal decay and hyaluronan synthesis inhibition in cycloheximide-treated cells. The transfer from ER to Golgi took about 1 h, and the dwell time on the plasma membrane was less than 2 h in experiments with a relief and introduction, respectively, of brefeldin A. Constructs of HAS3 with 16- and 45-amino-acid C-terminal deletions mostly stayed within the ER, whereas a D216A missense mutant was localized within the Golgi complex but not the plasma membrane. Both types of mutations were almost or completely inactive, similar to the wild type enzyme that had its entry to the plasma membrane experimentally blocked by brefeldin A. Inhibition of hyaluronan synthesis by UDP-glucuronic acid starvation using 4-methyl-umbelliferone also prevented HAS access to the plasma membrane. The results demonstrate that 1) a latent pool of HAS exists within the ER-Golgi pathway; 2) this pool can be rapidly mobilized and activated by insertion into the plasma membrane; and 3) inhibition of HAS activity through mutation or substrate starvation results in exclusion of HAS from the plasma membrane.     

Hypothesis: a phospholipid translocase couples lateral and transverse bilayer asymmetries in dividing bacteria

Cell division in bacteria such as Escherichia coli entails changes in the radii of curvature of the invaginating cytoplasmic membrane which culminate in rearrangements of its monolayers. Division therefore risks perturbing transverse and lateral asymmetries and compromising membrane integrity. This leads us to propose that a strong selective pressure exists for a phospholipid translocator that would transfer phospholipids across the cytoplasmic membrane so as to both demarcate the division site and mediate lipid composition during division. This translocase has an affinity for phospholipids with small headgroups and unsaturated acyl chains which it translocates so as to (1) generate changes in the radius of curvature, (2) facilitate septum formation, (3) minimise bilayer disruption during fusion and (4) prevent septum formation at old or inappropriate division sites. We discuss briefly possible candidates for this translocase including ABC transporters and proteins localised to the division site.     

Environmental tolerances of an invasive terrestrial amphipod, Arcitalitrus dorrieni (Hunt) in Britain

We investigated key physiological tolerances of the invasive euterrestrial talitrid amphipod (or landhopper) Arcitalitrus dorrieni; desiccation, salt, high and low temperatures. The critical relative humidity below which, A. dorrieni experiences desiccation stress is very high (95-100%), making it completely reliant on the leaflitter/soil microhabitat. It is tolerant of a wide range of (sea) salt concentrations (5-750 mOsmol l(-1)) but is extremely vulnerable below 5 mOsmol l(-1). A. dorrieni does not tolerate low temperatures with a mean lower limit of 1.4 degrees C, but with no individual surviving <0 degrees C. The range of upper thermal tolerance (30-37.3 degrees C) was similar to that found for other landhopper and beachflea species. Based on its tolerance to these environmental factors it is suggested that A. dorrieni has a limited potential to invade further into Britain, being restricted to areas with sufficiently high ion concentrations and mild winters.     

Serum zinc in healthy Belgian children

Many reports mention marginal zinc status in childhood. Information on serum zinc (Zn) in Belgian children since the last reports are old and feeding habits are changing. Four hundred fifty-seven healthy children (0-14 yr, 262 boys) had a venipuncture after an overnight fast during a vaccination campaign. Serum Zn, alpha-tocopherol (alpha-T), cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), apolipoprotein B (Apo B), Apo A, and malondialdehyde (MDA) were determinated. The median Zn value is lower in infants than in older children (respectively 11.6 micromol/L vs 12.8 micromol/L). The type of infant feeding does not influence the serum Zn concentrations (breast-feeding, adapted, hypoallergenic, soy, or thickened). No children had increased serum MDA concentrations and the value is not influenced by the Zn concentration. Children presenting higher serum Zn values also have significantly higher serum alpha-T levels. In infants, there is a significant positive correlation between serum Zn and cholesterol, LDL-C, and Apo B. In this apparently healthy population, no signs of abnormal in vivo peroxidation of fatty acids are observed, even in the children with low serum Zn. More sensitive methods for the detection of peroxidation are necessary for determination of in vivo effects of marginal trace element status.     

Cultural Specificity and Comparison in Psychiatric Epidemiology: Walking the Tightrope in American Indian Research

Increasingly, the mental health needs of populations are measured using large-sample surveys with standardized measures and methods. Such efforts, however, rarely include sufficient number of smaller, culturally defined populations to draw defensible conclusions about their needs. Furthermore, without some adaptation, the standardized methods and measures may yield invalid results in such populations. Using a recently completed psychiatric epidemiology and services study with American Indian populations as a case example, this paper outlines issues facing epidemiologists working in such culturally diverse contexts. The issues discussed include the following: (1) persuading the scientific community and potential sponsors that work with distinct or culturally defined populations is important; (2) framing research questions and activities to meet the needs of communities; (3) defining a population of inference; (4) balancing the needs for comparability and cultural specificity; (5) maximizing scientific validity in light of the challenges in sample acquisition; and (6) developing and implementing data collection methods that uphold scientific standards but are also realistic given the context. The authors draw on their experiences—most recently in the American Indian Service Utilization, Psychiatric Epidemiology, Risk and Protective Factors Project (AI-SUPERPFP)—to illustrate these issues and suggest ways to address each. A goal of this paper is to challenge those invested in conducting culturally valid epidemiologic work in such populations to better articulate the nature of these efforts.     

Structural basis for salinity-induced alteration in oxygen binding by haemocyanin from the estuarine amphipod Chaetogammarus marinus (L.)

In the estuarine amphipod Chaetogammarus marinus, differences in O(2) binding by haemocyanins (Hc) could be related to natural and salinity-related quantitative variation in just one polypeptide subunit (band 2) and not to variations in any of the other seven bands present. Band 2 was always present, irrespective of salinity treatment, and naturally makes up 6%-36% of the total Hc. However, low salinity exposure (S=4 per thousand for 48-49 h, T=15 degrees C) was accompanied by an increase in the prevalence of greater concentrations of band 2 (i.e., range, 20%-36% of total Hc present) and a concomitant increase in Hc-O(2) affinity (half saturation [P(50)] decreased from 1.38 to 1.12 kPa at pH=7.81, T=15 degrees C). A similar salinity-related mechanism (that is, one band altering) has been shown previously for the blue crab Callinectes sapidus, although the functional consequences were different. In contrast with C. marinus, an increase in the proportion of one polypeptide subunit in C. sapidus resulted in a decrease in Hc-O(2) affinity. This study has confirmed that between-individual variation (quantitative rather than qualitative) in just one Hc subunit may have functional consequences, although the significance of such variation is difficult to interpret.     

Effect of follicle size on in vitro production of steroids and insulin-like growth factor (IGF)-I,IGF-II,and the IGF-binding proteins by equine ovarian granulosa cells

Little is known regarding the hormonal regulation of granulosa cell steroidogenesis and the ovarian insulin-like growth factor (IGF) system in the mare. The objectives of this study were to determine, first, if estradiol, insulin, and/or FSH affect steroid production by equine granulosa cells (experiment 1) and, second, if the components of the IGF system are produced by equine granulosa cells in culture as well as whether estradiol, insulin, and/or FSH affects IGF and/or IGF-binding protein (IGFBP) production by equine granulosa cells (experiment 2). Granulosa cells from small (6-15 mm), medium (16-25 mm), and large (25-48 mm) follicles were collected from cyclic mares (n = 14), cultured for 2 days in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 days in serum-free medium with or without added hormones. In experiment 1, large-follicle granulosa cells produced less progesterone and more estradiol than did medium- and/or small-follicle granulosa cells (P < 0.05). Progesterone production was inhibited (P < 0.05) by FSH and insulin in small- and medium- but not in large-follicle granulosa cells; estradiol was without effect. Insulin increased (P < 0.05) estradiol production in small- and medium-follicle granulosa cells but had no effect in large-follicle granulosa cells. In experiment 2, IGF-I production was inhibited (P < 0.05) by insulin across all follicle sizes but was not affected by estradiol or FSH. Granulosa cells of medium and large follicles produced more IGF-II than did granulosa cells of small follicles (P < 0.05). Insulin and FSH inhibited (P < 0.05) IGF-II production by granulosa cells of large and medium but not of small follicles; estradiol was without effect. Only IGFBP-2 and -5 were produced by equine granulosa cells. Production of IGFBP-2 was less (P < 0.10) in granulosa cells of large versus those of small and medium follicles, whereas medium-follicle granulosa cells produced more (P < 0.05) IGFBP-5 than did small- or large-follicle granulosa cells. Averaged across follicle sizes, estradiol increased (P < 0.05) IGFBP-2 production, FSH increased (P < 0.10) IGFBP-2 and -5 production, and insulin was without effect. These results indicate that IGF-I, IGF-II, IGFBP-2, and IGFBP-5 are produced by equine granulosa cells and that insulin, FSH, and estradiol play a role in the regulation of steroidogenesis and the IGF system of equine granulosa cells.