Interfacial instability and the agglutination of erythrocytes by polylysine

Human erythrocytes have been exposed to poylysine of molecular weight range 4 to 220 kDa and concentration range 0.5 to 2,000 /ml at 37°C. Threshold concentrations for cell agglutination by the polycation have been determined for the samples of different molecular weight. Light and electron micrographs show that, in the erythrocyte agglutinates, cell-cell contact is generally made only at discrete, spatially periodic, regions which are distributed over a significant part of the cell surface. The average spacing between contact regions is 0.83 m. The cell membrane has a wavy profile between contact regions. Agglutination occurs only in cell samples whose electrophoretic mobility is significantly altered by polylysine and, in agreement with a previous report, occurs even when the electrophoretic mobility reaches high positive values. The electrophoretic mobility data implies that agglutination requires some protrusion of polylysine from the cell glycocalyx. We discuss how a resulting net attractive intercellular force could act to destabilize the aqueous layer between two cells, allowing surface wave growth which results in spatially periodic contact regions. Examples of situations where cell and membrane contact might be explained by the general concept of interfacial instability are discussed.     

Inbreeding alters intersexual fitness correlations in Drosophila simulans.

Intralocus sexual conflict results from sexually antagonistic selection on traits shared by the sexes. This can displace males and females from their respective fitness optima, and negative intersexual correlations (r_mf) for fitness are the unequivocal indicator of this evolutionary conflict. It has recently been suggested that intersexual fitness correlations can vary depending on the segregating genetic variation present in a population, and one way to alter genetic variation and test this idea is via inbreeding. Here, we test whether intersexual correlations for fitness vary with inbreeding in Drosophila simulans isolines reared under homogenous conditions. We measured male and female fitness at different times following the establishment of isofemale lines and found that the sign of the association between the two measures varied with time after initial inbreeding. Our results are consistent with suggestions that the type of genetic variation segregating within a population can determine the extent of intralocus sexual conflict and also support the idea that sexually antagonistic alleles segregate for longer in populations than alleles with sexually concordant effects.     

Tissue culture adherence and haemagglutination characteristics of Moraxella (Branhamella) catarrhalis

The haemagglutination and tissue culture adherence properties of 20 isolates of Moraxella catarrhalis obtained from the sputum of elderly patients with lower respiratory tract infections were compared with those of 20 isolates of M. catarrhalis obtained from the nasopharynx of elderly persons colonised by the organism. Eighty percent of isolates from the infected group as opposed to 5% of isolates from the colonised group haemagglutinated human erythrocytes (P < 0.001), indicating that the haemagglutinin might be a marker of pathogenicity for M. catarrhalis. There was a significant difference in the adherence to HEp-2 cells of isolates from the infected group in comparison to isolates from the colonised group (P = 0.03). Haemagglutination and tissue culture adherence properties were unrelated, indicating that separate adhesin systems are involved. The adherence of M. catarrhalis to HEp-2 cells was unaffected following pronase and trypsin treatment, however, sodium periodate pre-treatment of the bacteria significantly reduced the tissue culture adherence index, indicating that the adhesin by which the bacteria bind to HEp-2 cells may have a carbohydrate moiety. Transmission electron microscopy studies revealed that adherence of M. catarrhalis to HEp-2 cells was mediated by trypsin-resistant 'tack-/spicule-like' structures protruding from the surface of the bacteria.     

Interfacial instability and membrane internalization in human erythrocytes heated in the presence of serum albumin

The dynamics of morphological change, when human erythrocytes are heated through the spectrin denaturation temperature in the presence of bovine serum albumin, has been studied using differential interference contrast optics and a television video analysis system. Most washed (control) cells developed a wavy disturbance, with an average of $\text{6.6 ± 0.4}$ (2 S.E.) waves per cell rim, when heated. The average number of waves per cell rim decreased and the percentage of heated cells showing morphological changes in the dimple region increased with increasing serum albumin concentration, reaching 100% at 1.0 g/l. The change in the dimple region of cells heated in the presence of serum albumin involved the growth of a regular wavy disturbance around the cell dimple rim. The development of the wavy disturbance on the dimple, which resulted in the internalization of membrane, has been examined as an example of an interfacial instability on a biological membrane. Scanning and transmission electron micrographs confirm membrane internalization.     

Predicting the consequences of species loss using size‐structured biodiversity approaches

Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait‐free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size‐spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re‐assess three classic debates on the relationships between biodiversity and (i) food‐web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size‐structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body‐mass distributions maintaining food‐web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock‐on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size‐structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss.     

Methylenetetrahydrofolate reductase 677C-->T polymorphism affects DNA methylation in response to controlled folate intake in young women

DNA methylation is critical for normal genomic structure and function and is dependent on adequate folate status. A polymorphism (677C-->T) in a key folate enzyme, methylenetetrahydrofolate reductase (MTHFR), may impair DNA methylation when folate intake is inadequate and may increase the risk of reproductive abnormalities. The present study was designed to evaluate the effect of the MTHFR 677C-->T polymorphism on changes in global DNA methylation in young women consuming a low folate diet followed by repletion with the current Recommended Dietary Allowance (RDA). Women (age 20-30 years) with the TT (variant; n = 19) or CC (n = 22) genotype for the MTHFR 677C-->T polymorphism participated in a folate depletion-repletion study (7 weeks, 115 microg DFE/day; 7 weeks, 400 microg DFE/day). DNA methylation was measured at baseline, week 7, and week 14 using a [3H]methyl acceptance assay and a novel liquid chromatography tandem mass spectrometry assay of the DNA bases methylcytosine and cytosine. [3H]Methyl group acceptance tended to increase (P = 0.08) during depletion in all subjects, indicative of a decrease in global DNA methylation. During repletion, the raw change and the percent change in the methylcytosine/total cytosine ratio increased (P = 0.03 and P = 0.04, respectively) only in the subjects with the TT genotype. Moderate folate depletion in young women may cause a decrease in overall DNA methylation. The response to folate repletion suggests that following folate depletion women with the MTHFR 677 TT genotype have a greater increase in DNA methylation with folate repletion than women with the CC genotype.     

A comprehensive classification system for lipids

Lipids are produced, transported, and recognized by the concerted actions of numerous enzymes, binding proteins, and receptors. A comprehensive analysis of lipid molecules, "lipidomics," in the context of genomics and proteomics is crucial to understanding cellular physiology and pathology; consequently, lipid biology has become a major research target of the postgenomic revolution and systems biology. To facilitate international communication about lipids, a comprehensive classification of lipids with a common platform that is compatible with informatics requirements has been developed to deal with the massive amounts of data that will be generated by our lipid community. As an initial step in this development, we divide lipids into eight categories (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, saccharolipids, and polyketides) containing distinct classes and subclasses of molecules, devise a common manner of representing the chemical structures of individual lipids and their derivatives, and provide a 12 digit identifier for each unique lipid molecule. The lipid classification scheme is chemically based and driven by the distinct hydrophobic and hydrophilic elements that compose the lipid. This structured vocabulary will facilitate the systematization of lipid biology and enable the cataloging of lipids and their properties in a way that is compatible with other macromolecular databases.     

Molecular adhesion development in a neural cell monolayer forming in an ultrasound trap

A 2-dimensional aggregate of C6 neural cells was formed rapidly (within 30 s) in suspension in a recently developed 1.5 MHz ultrasound standing wave trap. A typical 1 mm diameter aggregate contained about 3,500 cells. Spreading of membrane occurred between the aggregated cells. The rate of spreading of the tangentially developing intercellular contact area was 0.19 microm/min. The form of the suspended aggregate changed from one of a hexagonal arrangement of cells to one of a cell-monolayer-like continuous sheet of mostly quadrilateral and pentagonal cells as in a cell monolayer on a solid substratum. A range of fluorescent indicators showed that the >99% viability of the cells did not change during 1 h exposures; therefore cell viability was not compromised during the monolayer development. The average integral intensities from stained actin filaments at the spreading cell-cell interfaces after 1, 8 and 30 min were 14, 25 and 46 microm(2) respectively. The cells in this work progressed from physical aggregation, through molecular adhesion, to displaying the intracellular consequences of receptor interactions. The ability to form mechanically strong confluent monolayer structures that can be monitored in situ or harvested from the trap provides a technique with general potential for monitoring the synchronous development of cell responses to receptor-triggered adhesion.