Why do microorganisms have aquaporins?

Aquaporins are channel proteins that enhance the permeability of cell membranes for water. They have been found in Bacteria, Archaea and Eukaryotes. However, their absence in many microorganisms suggests that aquaporins do not fulfill a broad role such as turgor regulation or osmoadaptation but, instead, fulfill a role that enables microorganisms to have specific lifestyles. The recent discovery that aquaporins enhance cellular tolerance against rapid freezing suggests that they have ecological relevance. We have identified several examples of large-scale freeze-thawing of microbes in nature and we also draw attention to alternative lifestyle-related functions for aquaporins, which will be a focus of future research.     

Why does a nematode have an invariant cell lineage?

C. elegans is renowned for its invariant embryogenesis and functions as a major paradigm for a mode of development coupled to an invariant lineage. Recent work, however, suggests that the embryogenesis of the nematode is much more flexible than anticipated. The invariant premorphogenetic stage is formed from variable earlier stages through a sorting of cells. Cells do not act as individuals but already early in embryogenesis a regionalization of the embryo occurs. Cells are diversified by a binary specification of 'abstract' blastomere (regional) identities. The determination of tissues may thus be a very late event. It appears that C. elegans, although assigning cell fates in an invariant lineage pattern, uses the same strategies and mechanisms for embryogenesis as organisms with variable lineages.     

Why does the brain (not) have glycogen?

In the present paper we formulate the hypothesis that brain glycogen is a critical determinant in the modulation of carbohydrate supply at the cellular level. Specifically, we propose that mobilization of astrocytic glycogen after an increase in AMP levels during enhanced neuronal activity controls the concentration of glucose phosphates in astrocytes. This would result in modulation of glucose phosphorylation by hexokinase and upstream cell glucose uptake. This mechanism would favor glucose channeling to activated neurons, supplementing the already rich neuron-astrocyte metabolic and functional partnership with important implications for the energy compounds used to sustain neuronal activity. The hypothesis is based on recent modeling evidence suggesting that rapid glycogen breakdown can profoundly alter the short-term kinetics of glucose delivery to neurons and astrocytes. It is also based on review of the literature relevant to glycogen metabolism during physiological brain activity, with an emphasis on the metabolic pathways identifying both the origin and the fate of this glucose reserve.     

Hawthorn special extract WS? 1442 increases red blood cell NO-formation without altering red blood cell deformability

WS(?) 1442 is a special extract of hawthorn leaves with flowers used for the treatment of mild cardiac failure. The activation of endothelial nitric oxide synthase (eNOS) has been shown to contribute to its vasodilating properties. Quite recently it has been demonstrated that red blood cells (RBCs) express a functional NO-synthase (rbcNOS) and rbcNOS activation has been associated with increased RBC deformability. The aim of the present study was to determine whether WS(?) 1442 is able to activate rbcNOS, to induce NO-formation in RBC and to alter RBC-deformability. Blood from healthy volunteers was incubated with WS(?) 1442 (25-100 μg/ml) for up to 30 min. RbcNOS activation was detected by immunohistochemical staining of phosphorylated rbcNOS and NO-formation was examined by diaminofluorescein (DAF) fluorescence. RBC deformability was measured by a laser assisted optical rotational cell analyzer. Serine 1177 of RbcNOS (rbcNOS Ser(1177)) was time- and concentration-dependently phosphorylated by WS(?) 1442. Rates of rbcNOS Ser(1177) phosphorylation were up to 149% higher in RBCs treated with WS(?) 1442 in comparison to control (DMSO 0.05%). WS(?) 1442 induced a time-dependent increase in NO-formation in RBCs which reached its maximum after 5 min. An increase in shear stress (0.3-50 Pa) caused an increase in RBC deformability. WS(?) 1442 did not change either basal or maximal RBC-deformability or shear stress sensitivity of RBC at normoxia. CONCLUSION: WS(?) 1442 activates rbcNOS and causes NO-formation in RBCs. WS(?) 1442-dependent NO-formation however does not affect RBC-deformability at normoxia.     

Where does blood go? Prospective observational study of red cell transfusion in north England

ObjectiveTo collect population based information on transfusion of red blood cells.DesignProspective observational study over 28 days.SettingHospital blood banks in the north of England (population 2.9 million).ParticipantsAll patients who received a red cell transfusion during the study period. Data completed by hospital blood bank staff.ResultsThe destination of 9848 units was recorded (97% of expected blood use). In total 9774 units were transfused: 5047 (51.6%) units were given to medical patients, 3982 (40.7%) to surgical patients, and 612 (6.3%) to obstetric and gynaecology patients. Nearly half (49.3%) of all blood is given to female recipients, and the mean age of recipients of individual units was 62.7 years. The most common surgical indications for transfusion were total hip replacement (4.6% of all blood transfused) and coronary artery bypass grafting (4.1%). Haematological disorders accounted for 15.5% of use. Overall use was 4274 units per 100 000 population per year.ConclusionIn the north east of England more than half of red cell units are transfused for medical indications. Demand for red cell transfusion increases with age. With anticipated changes in the age structure of the population the demand for blood will increase by 4.9% by 2008.

What is already known on this topic

There have been no systematic population based surveys on use of red cells in the United KingdomStudies in France and the United States have shown that more than half of transfused red cells go to surgical patients

What this study adds

In the north of England over half of red cells are given for medical indicationsRates of red cell transfusion rise steeply with advancing ageSmall increases in the number of elderly people will have large effects on demand     

How many pathways for invasion of the red blood cell by the malaria parasite?

Merozoites of the malaria parasite Plasmodium falciparum use several receptors for cellular engagement when they invade human red blood cells. Recently, a merozoite erythrocyte-binding protein, EBA-140, has been identified that specifically binds to glycophorin C on red blood cells. Up to 50% of Melanesians have a deletion in this gene, and the resultant Gerbich-negative red blood cells are relatively resistant to invasion. While discovery of multiple pathways for invasion could confound the search for suitable vaccine targets, they could also be considered in the design of therapeutic interventions that prevent malaria parasites entering red blood cells.     

Motile systems in malaria merozoites: how is the red blood cell invaded?

The ability of the malaria parasite to invade erythrocytes is central to the disease process, but is not thoroughly understood. In particular, little attention has been paid to the motor systems driving invasion. Here, Jennifer Pinder, Ruth Fowler and colleagues review motility in the merozoite. The components of an actomyosin motor are present, including a novel unconventional class XIV myosin, now called Pfmyo-A, which, because of its time of synthesis and location, is likely to generate the force required for invasion. In addition, there is a subpellicular microtubule assemblage in falciparum merozoites, the f-MAST, the integrity of which is necessary for invasion.     

Why does the biota of the Madagascar region have such a strong Asiatic flavour?

A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite Madagascar’s extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post‐date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea‐level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota. © The Willi Hennig Society 2009.     

How should the optical tweezers experiment be used to characterize the red blood cell membrane mechanics?

Stretching red blood cells using optical tweezers is a way to characterize the mechanical properties of their membrane by measuring the size of the cell in the direction of the stretching (axial diameter) and perpendicularly (transverse diameter). Recently, such data have been used in numerous publications to validate solvers dedicated to the computation of red blood cell dynamics under flow. In the present study, different mechanical models are used to simulate the stretching of red blood cells by optical tweezers. Results first show that the mechanical moduli of the membranes have to be adjusted as a function of the model used. In addition, by assessing the area dilation of the cells, the axial and transverse diameters measured in optical tweezers experiments are found to be insufficient to discriminate between models relevant to red blood cells or not. At last, it is shown that other quantities such as the height or the profile of the cell should be preferred for validation purposes since they are more sensitive to the membrane model.     

Why does mitochondrial complex I have so many subunits?

The prokaryotic and eukaryotic homologues of complex I (proton-pumping NADH:quinone oxidoreductase) perform the same function in energy transduction, but the eukaryotic enzymes are twice as big as their prokaryotic cousins, and comprise three times as many subunits. Fourteen core subunits are conserved in all complexes I, and are sufficient for catalysis - so why are the eukaryotic enzymes embellished by so many supernumerary or accessory subunits? In this issue of the Biochemical Journal, Angerer et al. have provided new evidence to suggest that the supernumerary subunits are important for enzyme stability. This commentary aims to put this suggestion into context.     

Why does the species problem still persist?

Despite many years of discussion, the species problem has still not been adequately resolved. Why is this the case? Here I discuss two recent suggested answers to this question that place the blame on the species problem's empirical aspects or on its philosophical aspects. In contrast, I argue that neither of these two faces of the species problem constitute the principal cause of the species problem's persistence. Rather, they are merely symptoms of the real cause: the species problem has not yet gone away because of a failure to recognize that not one but a number of distinct concepts are at the heart of the problem. To illustrate this point, a recently proposed solution to the problem is examined: the suggestion to understand the concept of species as a family resemblance concept. BioEssays 26:300–305, 2004. © 2004 Wiley Periodicals, Inc.