Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation.

The Earth's inner core grows by the freezing of liquid iron at its surface. The point in history at which this process initiated marks a step-change in the thermal evolution of the planet. Recent computational and experimental studies have presented radically differing estimates of the thermal conductivity of the Earth's core, resulting in estimates of the timing of inner-core nucleation ranging from less than half a billion to nearly two billion years ago. Recent inner-core nucleation (high thermal conductivity) requires high outer-core temperatures in the early Earth that complicate models of thermal evolution. The nucleation of the core leads to a different convective regime and potentially different magnetic field structures that produce an observable signal in the palaeomagnetic record and allow the date of inner-core nucleation to be estimated directly. Previous studies searching for this signature have been hampered by the paucity of palaeomagnetic intensity measurements, by the lack of an effective means of assessing their reliability, and by shorter-timescale geomagnetic variations. Here we examine results from an expanded Precambrian database of palaeomagnetic intensity measurements selected using a new set of reliability criteria. Our analysis provides intensity-based support for the dominant dipolarity of the time-averaged Precambrian field, a crucial requirement for palaeomagnetic reconstructions of continents. We also present firm evidence for the existence of very long-term variations in geomagnetic strength. The most prominent and robust transition in the record is an increase in both average field strength and variability that is observed to occur between a billion and 1.5 billion years ago. This observation is most readily explained by the nucleation of the inner core occurring during this interval; the timing would tend to favour a modest value of core thermal conductivity and supports a simple thermal evolution model for the Earth.

Characterization and implications of intradecadal variations in length of day.

Variations in Earth's rotation (defined in terms of length of day) arise from external tidal torques, or from an exchange of angular momentum between the solid Earth and its fluid components. On short timescales (annual or shorter) the non-tidal component is dominated by the atmosphere, with small contributions from the ocean and hydrological system. On decadal timescales, the dominant contribution is from angular momentum exchange between the solid mantle and fluid outer core. Intradecadal periods have been less clear and have been characterized by signals with a wide range of periods and varying amplitudes, including a peak at about 6 years (refs 2-4). Here, by working in the time domain rather than the frequency domain, we show a clear partition of the non-atmospheric component into only three components: a decadally varying trend, a 5.9-year period oscillation, and jumps at times contemporaneous with geomagnetic jerks. The nature of the jumps in length of day leads to a fundamental change in what class of phenomena may give rise to the jerks, and provides a strong constraint on electrical conductivity of the lower mantle, which can in turn constrain its structure and composition.

Fatigue in patients with spinal muscular atrophy type II and congenital myopathies: evaluation of the fatigue severity scale.

PURPOSE: The aim of this study was to evaluate whether the fatigue severity scale (FSS) is an appropriate instrument to assess fatigue in patients with spinal muscular atrophy type II (SMA II) and congenital myopathies (CM). METHODS: FSS and visual analog scale (VAS) were administered to 33 SMA II- and 72 CM patients. The psychometric properties of the FSS were evaluated by means of classical test theories for each of the disease groups. If abnormal fatigue was present in the disease group, the construct of fatigue was evaluated by means of focus group interviews. RESULTS: Fatigue was rare in SMA II patients, but very frequent in patients with CM. The cut-off score designating abnormal fatigue (FSS score ≥ 4) was exceeded by 10% of the SMA II patients in contrast to 76% of the CM patients, of whom 52% suffered from severe fatigue (FSS score ≥ 5). Focus group interviews demonstrated that fatigue had an adverse effect on motor function, level of energy, social relations, and identity, four themes that could be captured by the FSS. The FSS and VAS were strongly correlated in SMA II patients, but only moderately in CM patients. The psychometric properties indicated that the original FSS with nine items measures more than one construct of fatigue, eliminating the first two items improved scale properties. CONCLUSION: This study demonstrates that fatigue is characteristic in patients with CM, but not in patients with SMA II, in whom fatigue does not seem to impact daily life. While fatigue in CM and SMA II can be captured by FSS, omitting the first two items of the scale will improve its properties and content validity, along with comprehension of the scale itself.

Mutations in Cdh23, encoding a new type of cadherin, cause stereocilia disorganization in waltzer, the mouse model for Usher syndrome type 1D.

Mouse chromosome 10 harbors several loci associated with hearing loss, including waltzer (v), modifier-of deaf waddler (mdfw) and Age-related hearing loss (Ahl). The human region that is orthologous to the mouse 'waltzer' region is located at 10q21-q22 and contains the human deafness loci DFNB12 and USH1D). Numerous mutations at the waltzer locus have been documented causing erratic circling and hearing loss. Here we report the identification of a new gene mutated in v. The 10.5-kb Cdh23 cDNA encodes a very large, single-pass transmembrane protein, that we have called otocadherin. It has an extracellular domain that contains 27 repeats; these show significant homology to the cadherin ectodomain. In v(6J), a GT transversion creates a premature stop codon. In v(Alb), a CT exchange generates an ectopic donor splice site, effecting deletion of 119 nucleotides of exonic sequence. In v(2J), a GA transition abolishes the donor splice site, leading to aberrant splice forms. All three alleles are predicted to cause loss of function. We demonstrate Cdh23 expression in the neurosensory epithelium and show that during early hair-cell differentiation, stereocilia organization is disrupted in v(2J) homozygotes. Our data indicate that otocadherin is a critical component of hair bundle formation. Mutations in human CDH23 cause Usher syndrome type 1D and thus, establish waltzer as the mouse model for USH1D.

Genes involved in deafness.

Remarkable progress has been made over the past few years in the field of hereditary deafness. To date, mutations in at least 35 genes are known to cause hearing loss. We are now beginning to understand the function of many of these genes, which affect diverse aspects of ear development and function.

Ectopic expression of Msx2 in chick retinal pigmented epithelium cultures suggests a role in patterning the optic vesicle.

During the initial stages of vertebrate retinogenesis, cells of the optic vesicle adopt one of two alternate cell fates. Cells in the distal-most part of the vesicle, immediately beneath the surface ectoderm, undergo neural differentiation; cells in the proximal part differentiate into retinal pigmented epithelial cells. The mechanisms that establish this pattern of differentiation are poorly understood. In the mouse embryo, Msx2, a homeobox-containing transcription factor, is expressed in cells of the optic vesicle that will form the neural retina, whilst the developing retinal pigmented epithelium (RPE) does not express this gene. Msx2 could therefore be involved in patterning the optic vesicle into neural and pigmented domains. To explore this possibility we ectopically expressed mouse Msx2 in cultures of chick RPE cells. Compared with cultures transfected with a control construct, Msx2-transfected cultures contained fewer cells expressing the RPE marker, Mitf, and more cells expressing class III beta-tubulin, a neuronal marker. In addition a small proportion of Msx2-transfected cells acquired a neural-like morphology. These results show that Msx2 can suppress the differentiated state of RPE cells and promote their differentiation into neural cell types. We suggest that Msx2 may pattern the optic vesicle into neural and pigmented domains by affecting the balance between RPE and neural retina differentiation.

In vitro interaction between cultured cells and human blood platelets.

The effects of washed human cultured cells (tumour cells and Chang liver cells) on human blood platelets in heparinized plasma were studied. Platelet aggregation was induced by suspensions of the tumour cells. Ultrastructural examination showed that the platelets, especially in the central regions of the aggregates, were tightly packed and the alpha-granules were mostly present. In the periphery of the aggregates the platelets appeared swollen and devoid of organelles, and fibrin strands were seen. The platelet aggregation was not completely abolished by incubation with apyrase. The washing fluids from the tumour cells also induced platelet aggregation, but the aggregation could be abolished by incubation with apyrase. When three different lines of the Chang cells were used, suspensions of two lines of these cells induced platelet aggregation, but the third line did not. Presence of ADP could be demonstrated in the washing fluids from the cultured cells, except for the one line of Chang cells which did not induce platelet aggregation. The experiments indicated that the platelet aggregation induced by the various types of cells was mediated via ADP, but with a possible additional effect of coagulation activity.

A comparison of en face and tangential wide-area excimer surface ablation in the rabbit.

We used an argon fluoride excimer laser (193 nm) to perform anterior corneal surface ablation in New Zealand white rabbits (25 eyes) using both en face and tangential methods. We followed up the animals for 90 days using slit-lamp photography and pachymetry at predetermined intervals. We also examined selected tissues with scanning electron microscopy and transmission electron microscopy. Immediate and subsequent examinations revealed significant differences in clarity between the two groups. When viewed through slit-lamp microscopy, the rabbits undergoing the en face method exhibited hazy corneas and irregular surfaces, whereas the corneas that underwent tangential keratectomy demonstrated less haze and fewer surface irregularities. Through histologic study and electron microscopy, we corroborated this finding. At 30 days, there was a statistically significant difference in clarity between en face--treated corneas and those treated tangentially.

The charge-heterogeneity of human fibrinogen as investigated by 2D electrophoresis.

The charge-heterogeneity of human plasma fibrinogen subunit chains was characterized by two-dimensional electrophoresis (2DE). Western blotting with antibodies specific for the gamma-chain demonstrated that the gamma-chains focus at varying isoelectric points (pI). This microheterogeneity was also observed in fibrinogen secreted from hepatocytic cells and in recombinant fibrinogen expressed in Chinese hamster ovary (CHO) cells. Further, covalent gammagamma-dimerization by FXIIIa was not influenced by the charge-heterogeneity, and removal of the carbohydrate did not reduce the number of gamma-chain pI variants. These observations suggest that the microheterogeneity of the gamma-chain is a multifactorial phenomenon that is not due to physiologic modification of the glycoprotein in circulation.

Triglyceride lipase activity in postheparin plasma and plasma lipoproteins in liver disease.

Hepatic lipase activity and lipoprotein lipase activity were studied in postheparin plasma from 14 patients with various liver disorders. Plasma lecithin: cholesterol acyltransferase (LCAT) activity and lipoprotein composition and structure were also estimated. Five patients had lower hepatic lipase activity than the lowest control value, and in three of these no hepatic lipase activity was detected. Lipoprotein lipase was low in 5 patients, but in only one of them was hepatic lipase activity also low. Hepatic lipase was not significantly correlated to the concentration of plasma triglycerides, either in controls or in patients, whereas lipoprotein lipase was negatively correlated with plasma triglycerides both in controls and patients. Lipoprotein lipase and LCAT activity, but not hepatic lipase, was negatively correlated to the triglyceride content of the low density lipoproteins (density 1.019-1.063 g/ml) from the patients. No specific lipid or lipoprotein pattern was found in plasma from the patients with a low or without any hepatic lipase activity. The results suggest an important role of lipoprotein lipase and LCAT, for the increased content of triglycerides in the low density lipoproteins in patients with liver disease. The role of hepatic lipase remains unclear.

The effect of lipoprotein lipase and hepatic lipase on the electrophoretic mobility of lipoprotein-X.

Lipoprotein-X containing plasma from a patient with familial lecithin:cholesterol acyltransferase (LCAT) deficiency, was used as substrate and incubated with postheparin plasma or partly purified lipases. LP-X could not be demonstrated by agar gel electrophoresis after incubation with postheparin plasma from a healthy subject, from a patient with chronic active hepatitis deficient in hepatic lipase, or with partly purified lipoprotein lipase. After incubation a marked increase in free fatty acids (FFA) was observed. In contrast LP-X was still present after incubation when postheparin plasma deficient in lipoprotein lipase or partly purified hepatic lipase was added to the substrate. Only minor changes in the concentration of FFA occurred. After addition of oleic acid to the substrate LP-X could not be demonstrated by agar gel electrophoresis. However, in the isolated low density lipoproteins, LP-X like particles were still present as viewed by electron microscopy. Our results strongly suggest that the change in electrophoretic mobility of LP-X was induced by the release of FFA. This was achieved by lipoprotein lipase, but not by hepatic lipase.

The electrophoretic mobility of lipoprotein X in postheparin plasma.

After incubation whole plasma and low density lipoproteins (LDL) taken before and 10 min after intravenous administration of heparin, from a patient with primary biliary cirrhosis and a patient with familial lecithin:cholesterol acyltransferase (LCAT) deficiency, have been tested for the presence of lipoprotein X (LP-X) by agar gel electrophoresis. LP-X was present in preheparin whole plasma and LDL. No precipitation lines on the cathodal side of the wells, indicating the absence of LP-X, were seen after electrophoresis of postheparin plasma and LDL. Immunodiffusion revealed the presence of apo-beta-lipoproteins and LP-X in preheparin as well as postheparin LDL. After gel filtration three subfractions and similar patterns were observed in the preheparin and postheparin LDL. Electronmicroscopical examination of the intermediate subfractions showed LP-X-like particles in preheparin and postheparin samples. These observations indicate a changed electrophoretic mobility in agar gel of postheparin LP-X, giving a false negative LP-X test by the conventional agar gel electrophoresis.

Familial lecithin:cholesterol acyltransferase deficiency. Further studies on plasma lipoproteins and plasma postheparin lipase activity of a patient with normal renal function.

Plasma lipoproteins and postheparin plasma were investigated in a patient with familial LCAT deficiency with normal renal function and without proteinuria. As revealed by gelfiltration the large molecular weight LDL2 was not present, and myelin structures were not found in LDL1 or LDL2 when she was on her ordinary diet. After 60--65% fat diet for one week the large molecular LDL2 was found, but only in low concentration. We have no explanation for the difference in the lipoprotein abnormalities of this patient and others with this disease. There is no major difference in the fat content in the ordinary diet of the Norwegian patients with familial LCAT deficiency, nor has our patient any clinical signs of malabsorption. Furthermore, there was no difference in lipoprotein lipase or hepatic lipase activity in postheparin plasma between our patient and others with the same disease. However, whereas hepatic lipase activity was within the reference values, lipoprotein lipase activity was rather low in all patients investigated. We suggest that impaired VLDL catabolism in plasma, because of LCAT deficiency and low lipoprotein lipase activity, may partly explain the low HDL concentration consistently found in patients with familial LCAT deficiency.

Drinking water contamination in Walkerton, Ontario: positive resolutions from a tragic event.

In May 2000, Escherichia coli O157:H7 and Campylobacter jejuni contaminated the drinking water supply in Walkerton, Ontario. Seven people died and over 2,000 were ill as a result. The Ontario Provincial Government set up a judicial Inquiry into the circumstances surrounding the outbreak and also moved quickly to introduce a new Drinking Water Regulation that incorporated some significant requirements for drinking water providers. The Inquiry itself was in three parts: (a) part 1 related to the events that occurred in Walkerton and why the water contamination occurred; (b) part 1A related specifically to the role of the Provincial Government in the event; and (c) part 2 related to the future of drinking water safety in Ontario with potential to influence regulation on a wider basis. A number of other actions were taken after Walkerton. In August 2000, the Ontario Government, through the Regulatory body, the Ontario Ministry of the Environment (MOE) (a) re-issued and revised the Ontario Drinking Water Objectives (ODWO) as the Ontario Drinking Water Standards (ODWS) and (b) introduced new regulations governing drinking water in Ontario--the Ontario Drinking Water Protection Regulation. One of the key features of the Drinking Water Protection Regulation was the requirement to produce an independent Engineers' Report on all water systems. This paper provides a unique perspective on the Walkerton tragedy and its aftermath. The author was active in many aspects of the resulting activity (Chair of the Ontario Water Works Association's (a section of the AWWA) Special Committee involved in Part 2 of the Walkerton Inquiry; author of several of the Engineers' Reports mandated by Regulation; reviewer on behalf of the Regulator of Engineers' Reports submitted by others). The Engineers' Reports were of interest because (1) the drinking water providers (mostly municipalities) were mandated by regulation to complete the Reports by specific dates and are paying for the Reports, (2) the work had to be done by a registered professional engineer who is not an employee of the owner or the operator if a different entity and (3) the engineer had to sign a declaration that the Regulator could rely on the accuracy of the Report. In other words, the Municipality retained the Engineer and paid them to produce the Report--the Engineer essentially carried the liability while the Regulator had the final say in the acceptability of the Report, a sort of eternal triangle of responsibilities. The paper will outline how the drinking water profession in North America worked together to provide the Walkerton Inquiry with the benefit of its experience and knowledge of best practices to the benefit of consumers and the drinking water providers. It will also outline the procedures adopted to produce the independent Engineers' Reports and how the findings are being applied to further improve drinking water safety in Ontario, across Canada and in similar situations around the world.

Effect of high-density lipoproteins on cholesterol efflux and esterification in lipid-enriched human skin fibroblasts.

The ability of high-density lipoprotein (HDL) to reduce the cholesterol content was studied in cultured fibroblasts enriched with cholesterol esters. Incubation of cholesterol-enriched cells with HDL in a final concentration of 1 g protein/l for 24 h reduced the total and esterified cholesterol content by 23% as compared with control fibroblasts incubated with albumin. Similar cholesterol efflux was obtained with HDL isolated from lecithin:cholesterol acyltransferase (LCAT)-deficient plasma. The HDL3 subfraction isolated by rate-zonal ultracentrifugation contained the major part of the cholesterol-depleting effect. HDL or HDL3 decreased CoA:cholesterol acyltransferase (ACAT) activity to 5% of the level found in control fibroblasts within 8 h of incubation. These findings suggest that ACAT activity is sensitive to a pool of intracellular cholesterol, which can be mobilized by the addition of HDL to the culture medium, and that ACAT activity is a useful measure of cholesterol efflux from cultured fibroblasts.