X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Alternative routes for the establishment of surface polarity during compaction of the mouse embryo

During the process of compaction, mouse 8-cell blastomeres flatten upon each other and polarize along an axis perpendicular to cell contacts. If the process of flattening is prevented, polarization can still occur, but does so in a lower proportion of cells than for control populations, and without the normal contact-directed orientation. We compared contact-directed and noncontact-directed processes to see if they involve common mechanisms. In nonflattened cells, surface polarization was favored in cells with nuclei located close to the cell surface, and the positions of surface poles and of nuclei tended to coincide. We present evidence that microtubules are involved in the development of microvillous poles associated with nuclei. In contrast it is known that polarization of microvilli occurs in the absence of microtubules if blastomeres are allowed to flatten. We conclude that surface polarization of mouse blastomeres can be accomplished by at least two alternative routes. One requires flattening but is independent of microtubules, and another can occur without flattening but involves a microtubule-mediated interaction between the nucleus and the cell cortex. It seems that both these pathways operate in the undisturbed embryo.     

The cytoskeleton, endocytosis and cell polarity in the mouse preimplantation embryo

The process of cell polarization in mouse 8-cell embryos includes the formation of a polar cluster of cytoplasmic endocytotic organelles (endosomes) subjacent to an apical surface pole of microvilli. A similar polar morphology, supplemented by basally localized secondary lysosomes, is evident following division to the 16-cell stage in outside blastomeres, precursors of the trophectodermal lineage. The roles of microfilaments and microtubules in generating and stabilizing endocytotic and surface features of polarity (visualized by horseradish peroxidase incubation and indirect immunofluorescence labeling, respectively) have been evaluated by exposure of 8- and 16-cell embryos and 8-cell couplets to drugs (cytochalasin D, colcemid, nocodazole) that disrupt the cytoskeleton. The generation of endocytotic polarity is dependent upon intact microtubules and microfilaments, but the newly established endocytotic pole in blastomeres from compacted 8-cell embryos appears to be stabilized exclusively by microtubules. Polarized endocytotic organelles at the 16-cell stage are more resistant to drug treatment than at the 8-cell stage (probably due to microfilament interactions) indicating a maturation phase in the polar cell lineage. Microtubules are also responsible for the orientation of endocytotic clusters along the cell's axis of polarity. In contrast, the generation and stability of polarity at the cell surface appears relatively independent of cytoskeletal integrity. The results are discussed in relation to the mechanisms that may control the development and stabilization of polarization during cleavage.     

Comparison of health problems related to work and environmental measurements in two office buildings with different ventilation systems.

A cross sectional survey investigating "building sickness" was carried out in two buildings with similar populations of office workers but differing ventilation systems, one being fully air conditioned with humidification and the other naturally ventilated. The prevalence of symptoms related to work was assessed by a questionnaire administered by a doctor. A stratified, randomly selected sample of workers was seen (84% response). Building sickness includes several distinct syndromes related to work, most of which were significantly more common in the air conditioned building than the naturally ventilated building--namely, rhinitis (28% v 5%), nasal blockage and dry throat (35% v 9%), lethargy (36% v 13%), and headache (31% v 15%). The prevalence of work related asthma and humidifier fever was low and did not differ significantly between the two buildings. An environmental assessment of the offices was performed to attempt to identify possible factors responsible for the differences in the prevalence of disease. Globe temperature, dry bulb temperature, relative humidity, moisture content, air velocity, positive and negative ions, and carbon monoxide, ozone, and formaldehyde concentrations were all measured. None of these factors differed between the buildings, suggesting that building sickness is caused by other factors.     

Sequence variation in the outer-surface-protein genes of Borrelia burgdorferi

Borrelia burgdorferi is a spirochete pathogen transmitted among warm- blooded hosts by ixodid ticks. Frequency-dependent selection for variant outer-surface proteins might be expected to arise in this species, since rare variants are more likely to avoid immune surveillance in previously infected hosts. We sequenced the OspA and OspB genes of nine North American strains and compared them with nine strains previously described. For each gene, the mean number of synonymous substitutions per synonymous site and the mean number of nonsynonymous substitutions per nonsynonymous site show only a twofold excess of silent mutations. Synonymous rates vary widely along the OspB protein. Some regions show a significant excess of silent substitutions, while divergence in other regions is constrained by biased base composition or selection. The presence, in antigenically important regions of the protein, of significant variation among strains, as well as evidence for recombination among strains, should be considered in attempts to develop vaccines against this disease.      

Characterisation of a 34 kD protein from potato cyst nematodes, using monoclonal antibodies with potential for species diagnosis

Two monoclonal antibodies, which differentially recognise the two species of potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, are described. They have been shown to have potential for quantification of these two species, recognising proteins of the same molecular weight (34 kD) in both species. Further investigation showed these proteins to have isoelectric points at pH values of 5.7 in G. pallida and 5.9 in G. rostochiensis, in common with the proteins used by Fleming & Marks (1983) to differentiate the species of PCN. They are likely to be structurally very similar, with the same physiological function (and therefore similar concentrations) in the two species. In cross-reactivity tests with a wide range of soil nematode species, the antibodies reacted strongly only with species of the genus Globodera, and thereby confirmed their potential as the basis of a quantitative immunoassay likely to be useful in management of PCN populations.     

Effects of endurance training on the cardiovascular system and water compartments in elderly subjects

Pickering, Gisèle P., Nicole Fellmann, BéatriceMorio, Patrick Ritz, Aimé Amonchot, Michel Vermorel, and JeanCoudert. Effects of endurance training on the cardiovascularsystem and water compartments in elderly subjects. J. Appl. Physiol. 83(4): 1300-1306, 1997.Theeffects of endurance training on the water compartments and thecardiovascular system were determined in 10 elderly subjects [age62 ± 2 yr, pretraining maximal oxygen consumption(O_{2 max})/kg = 25 ± 2 ml · min¹ · kg¹body wt]. They trained on a cycloergometer 3 times/wk for 16 wk(50-80%O_{2 max},then 80-85%O_{2 max}). They werechecked at 8 wk, 16 wk, and 4 mo after detraining. Training improvedO_{2 max} (+16%) andinduced plasma volume expansion (+11%). No change in total body water,extracellular fluid, interstitial and intracellular fluid volumes,fat-free mass, and body weight was detected in this small sample withtraining. Body fat mass decreased (2.1 ± 2.2 kg).Echocardiography at rest showed increased fractional shortening andejection fraction and decreased left ventricular end-systolic dimension(P < 0.05). Blood volume expansioncorrelates with cardiac contractility and has an impact on cardiacfunction. These improvements are precarious, however, and arecompletely lost after 4 mo of detraining, when elderly subjects losethe constraints and the social stimulation of the imposed protocol.

     

The sick building syndrome: prevalence studies.

Random samples or the entire workforce in nine offices in which similar clerical work was being performed were studied using a doctor administered questionnaire that inquired into symptoms that have been linked with the "sick building syndrome." Five of the offices were fully air conditioned, one had recirculation of air and mechanical ventilation, and three were naturally ventilated. Workers in three air conditioned and three naturally ventilated buildings were interviewed blind. Seven of the buildings were studied at our request in the absence of any known problem. Comparison of prevalences of symptoms between the naturally ventilated and the other buildings showed a repeated pattern of nasal, eye, and mucous membrane symptoms with lethargy, dry skin, and headaches. There were highly significant excesses of these six symptoms in the air conditioned buildings when compared by chi 2 tests with the naturally ventilated buildings. It is suggested that these six symptoms represent the sick building syndrome and that the size of the problem is probably greater than is currently recognised. Possible causes are discussed.     

Gap junction structures: Analysis of the x-ray diffraction data

Models for the spatial distribution of protein, lipid and water in gap junction structures have been constructed from the results of the analysis of X-ray diffraction data described here and the electron microscope and chemical data presented in the preceding paper (Caspar, D. L. D., D. A. Goodenough, L. Makowski, and W.C. Phillips. 1977. 74:605-628). The continuous intensity distribution on the meridian of the X-ray diffraction pattern was measured, and corrected for the effects of the partially ordered stacking and partial orientation of the junctions in the X-ray specimens. The electron density distribution in the direction perpendicular to the plane of the junction was calculated from the meridional intensity data. Determination of the interference function for the stacking of the junctions improved the accuracy of the electron density profile. The pair-correlation function, which provides information about the packing of junctions in the specimen, was calculated from the interference function. The intensities of the hexagonal lattice reflections on the equator of the X-ray pattern were used in coordination with the electron microscope data to calculate to the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profile and equatorial projections were shown to be correlated to changes in lattice constant. The parts of the junction structure which are variable have been distinguished from the invariant parts by comparison of the X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low resolution three- dimensional representations of the structures of gap junctions.