Do ants make direct comparisons?

Many individual decisions are informed by direct comparison of the alternatives. In collective decisions, however, only certain group members may have the opportunity to compare options. Emigrating ant colonies (Temnothorax albipennis) show sophisticated nest-site choice, selecting superior sites even when they are nine times further away than the alternative. How do they do this? We used radio-frequency identification-tagged ants to monitor individual behaviour. Here we show for the first time that switching between nests during the decision process can influence nest choice without requiring direct comparison of nests. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies chose the good nest. Switching by ants that had the opportunity to compare nests had little effect on nest choice. We suggest a new mechanism of collective nest choice: individuals respond to nest quality by the decision either to commit or to seek alternatives. Previously proposed mechanisms, recruitment latency and nest comparison, can be explained as side effects of this simple rule. Colony-level comparison and choice can emerge, without direct comparison by individuals.     

Do frogs make good canaries?

Coal miners used to take canaries with them into coal mines; more sensitive than humans to poisonous gases, they provided a living early-warning system. Are recent population declines among the world's frogs warning us of an environmental catastrophe to come?     

The choline transporter resurfaces: new roles for synaptic vesicles?

Presynaptic choline uptake is vital to sustained neuronal acetylcholine (ACh) release; however, only with the recent cloning of choline transporters (CHTs) (i.e., SLC5A7), has a picture emerged of the regulatory pathways supporting CHT modulation. Studies arising from the development of CHT-specific antibodies reveal a large, intracellular reserve of CHT proteins, localized to ACh-containing, synaptic vesicles. The intersection of mechanisms supporting vesicular ACh release and choline uptake demonstrates an elegant mechanism for linking regulation of CHT membrane density to rates of ACh release. Furthermore, these studies point to control of the CHT endocytic process as an important target for novel therapeutics that could offset functional deficits in disorders bearing diminished cholinergic tone, including myasthenias and dementias.     

Do mitochondria make nitric oxide? no?

Several papers have claimed that mitochondria contain nitric oxide synthase (NOS) and make nitric oxide (NO*) in amounts sufficient to affect mitochondrial respiration. However, we found that the addition of L-arginine or the NOS inhibitor L-NMMA to intact rat liver mitochondria did not have any effect on the respiratory rate in both State 3 and State 4. We did not detect mitochondrial NO* production by the oxymyoglobin oxidation assay, or electrochemically using an NO* electrode. An apparent NO* production detected by the Griess assay was identified as an artifact. NO* generated by eNOS added to the mitochondria could easily be detected, although succinate-supplemented mitochondria appeared to consume NO*. Our data show that NO* production by normal rat liver mitochondria cannot be detected in our laboratory, even though the levels of production claimed in the literature should easily have been measured by the techniques used. The implications for the putative mitochondrial NOS are discussed.     

Isoprenoid biosynthesis in bacteria: Two different pathways?

Abstract The biosynthesis of isopentenylpyrophosphate, a central intermediate of isoprenoid formation, was investigated in six different bacterial organisms. Cell-free extracts of Myxococcus fulvus, Staphylococcus carnosus, Lactobacillus plantarum and Halobacterium cutirubrum converted [¹⁴C]acetyl-CoA or [¹⁴C]hydroxymethylglutaryl-CoA to [¹⁴C]mevalonic acid. Furthermore, [¹⁴C]mevalonic acid, [¹⁴C]mevalonate-5-phosphate and [¹⁴C]mevalonate-5-pyrophosphate were metabolized to [¹⁴C]isopentenylpyrophosphate in bacteria. In contrast, no intermediates of this reaction sequence could be detected using cell-free extracts of Zymomonas mobilis and Escherichia coli . These results indicate that at least two different pathways for the biosynthesis of isopentenylpyrophosphate are present in bacteria.     

Do personal computers make doctors less personal?

Ten months after the installation of a computer in a general practice surgery a postal survey (piloted questionnaire) was sent to 390 patients. The patients'' views of their relationship with their doctor after the computer was introduced were compared with their view of their relationship before the installation of the computer. More than 96% of the patients (n=263) stated that contact with their doctor was as easy and as personal as before. Most stated that the computer did not influence the duration of the consultation. Eighty one patients (30%) stated, however, that they thought that their privacy was reduced.Unlike studies of patients'' attitudes performed before any actual experience of use of a computer in general practice, this study found that patients have little difficulty in accepting the presence of a computer in the consultation room. Nevertheless, doctors should inform their patients about any connections between their computer and other, external computers to allay fears about a decrease in privacy.     

Do mitochondria in Dendrobium petal mesophyll cells form vacuole-like vesicles?

Using transmission electron microscopy, we investigated the ultrastructure of mitochondria in petal mesophyll cells of the orchid Dendrobium cv. Lucky Duan, from the time of floral opening to visible petal senescence. Cells close to the vascular bundle contained many mitochondria, some of which showed internal degeneration. This inner mitochondrial breakdown was accompanied by an eightfold increase in mitochondrial volume. Small electron-dense granules (approximately 0.04 μm in diameter) at the periphery of the mitochondrial matrix remained. These granules were used as an indicator of still later stages of mitochondrial development in these cells. The apparent final stage of mitochondrial degeneration was a single-membrane-bound vesicle, resembling a vacuole. No evidence was found for the idea that mitochondria became transferred (intact or degenerated) into a lytic vacuole. Taken together, the data suggest the hypotheses that (a) mitochondria in cells close to the vascular bundle in petals of open Dendrobium cv. Lucky Duan flowers undergo large-scale internal degeneration and that (b) such degenerating mitochondria form vacuole-like vesicles.     

Do mammals make all their own inositol hexakisphosphate?

A highly specific and sensitive mass assay for inositol hexakisphosphate (InsP6) was characterized. This centres around phosphorylating InsP6 with [32P]ATP using a recombinant InsP6 kinase from Giardia lambia, followed by HPLC of the 32P-labelled products with an internal [3H]InsP7 standard. This assay was used to quantify InsP6 levels in a variety of biological samples.Concentrations of InsP6 in rat tissues varied from 10-20 microM (assuming 64% of wet weight of tissue is cytosol water), whereas using the same assumption axenic Dictyostelium discoideum cells contained 352 +/- 11 microM InsP6. HeLa cells were seeded at low density and grown to confluence, at which point they contained InsP6 levels per mg of protein similar to rat tissues. This amounted to 1.952 +/- 0.117 nmol InsP6 per culture dish, despite the cells being grown in serum shown to contain no detectable(less than 20 pmol per dish) InsP6. These results demonstrate that mammalian cells synthesize all their own InsP6. Human blood was analysed, and although the white cell fraction contained InsP6 at a concentration comparable with other tissues, in serum and platelet-free plasma no InsP6 was detected (<1 nM InsP6). Human urine was also examined, and also contained no detectable (<5 nM) InsP6. These results suggest that dietary studies purporting to measure InsP6 at micromolar concentrations in human plasma or urine may not have been quantifying this inositol phosphate. Therefore claims that administrating InsP6 in the diet or applying it topically can produce health benefits by increasing extracellular InsP6 levels may require reassessment.     

Do different surrogate methods detect lateral genetic transfer events of different relative ages?

Non-tree-based ("surrogate") methods have been used to identify instances of lateral genetic transfer in microbial genomes but agreement among predictions of different methods can be poor. It has been proposed that this disagreement arises because different surrogate methods are biased towards the detection of certain types of transfer events. This conjecture is supported by a rigorous phylogenetic analysis of 3776 proteins in Escherichia coli K12 MG1655 to map the ages of transfer events relative to one another.     

Do different branching epithelia use a conserved developmental mechanism?

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine-collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best-studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt.     

Do single mitochondria contain zones with different membrane potential?

Observations of Lan Bo Chen’s group using a mitochondria-selective fluorochrome 5,5’,6,6’- tetrachloro- 1,1’,3,3’- tetraethylbenzimidazolocarbocyanine iodide (JC-1) indicate that mitochondria in situ may have zones of different electrochemical potential along their length. This was indicated by the formation of J-aggregates of this dye at distinct sites along a single mitochondrion. Also, intensity variations along single mitochondria were found with diamino-styryl-pyridinium methiodide (DASPMI), another fluorochrome that selectively stains mitochondria depending on their electrochemical potential. DASPMI exchanges easily with the cytoplasm and changes its quantum yield when bound to mitochondrial membranes. Therefore, fluorescence intensity is primarily controlled by the membrane environment rather than by mass accumulation. Two possible explanations of intramitochondrial fluorescence intensity variations have to be discussed: variations in the amount of mitochondrial inner membrane per unit of projection area (or voxel), and differences in the electrochemical gradient. This problem has been approached by comparing fluoro-micrographs of mitochondria in endothelial cells stained with either JC-1 or DASPMI with electron micrographs of the same mitochondria after fixation with glutardialdehyde and osmium tetroxide and ultrathin sectioning. JC-1 red fluorescence (revealing J-aggregate formation) as well as high-intensity staining with DASPMI correlate roughly with the local thickness of mitochondria; no differences in the crista organization are revealed for those areas or mitochondria exhibiting red JC-1 fluorescence and those with green fluorescence. The distance between red fluorescing areas in a single mitochondrion seem to be caused by competition for dye molecules placed in between centres of JC-1 aggregation. Isolated mitochondria are of uniform small size and spherical shape; therefore, no differences in shape interfere with JC-1 staining. Thus JC-1 may be an appropriate indicator of membrane potential in isolated mitochondria. In living cells mitochondria often are large and elongated, and thus the situation is not straightforward to interpret. However, evidence is provided that there are submitochondrial zones, which differ in membrane potential from one adjacent area to another, because DASPMI staining of intramitochondrial zones reveals differences in fluorescence intensity and preferred photodamage of these areas. In some cases separation of the zones of higher membrane potential by cristae traversing the whole diameter of a mitochondrion has been observed. Local photobleaching of stained mitochondria results in a loss of fluorescence along the total length of a mitochondrion. However, this type of bleaching develops over tens of seconds, not in the very short time range (e.g. ms) expected from the discharge of all the membranes if they were electrically coupled.     

Do rodent and human brains have different N-glycosylation patterns?

A large number of studies on the structure of N-glycosidically linked oligosaccharides from glycoproteins of different organs and/or different species have been carried out in the past using various combinations of techniques such as monosaccharide analysis, permethylation, peracteylation, exoglycosidase sequencing, normal and reversed phase HPLC, mass spectrometry and nuclear magnetic resonance spectroscopy. Although it is widely accepted that the processing of N-glycans in the ER and Golgi of mammalian cells follows the same principal metabolic rules, analyses have revealed that the glycosylation pattern of a particular protein may differ depending on the cell type in which it is expressed. N-glycans from brain glycoproteins have been shown to include a variety of hybrid- and complex-type structures with structural features that are not so commonly found on glycoproteins from other organs and which have, therefore, been classified as 'brain-specific'. Comparison of the N-glycans of glycoproteins from homogenates of rat, mouse and human brains confirm that, in general, glycoproteins from human brain show a similar profile of brain-specific N-glycans as glycoproteins from mouse and rat brain.     

Do parasitoid preferences for different host species match virulence?

Abstract.  Leptopilina boulardi is a parasitoid wasp specialist of Drosophila larvae of the melanogaster subgroup. In Mediterranean areas, natural populations are highly virulent against their main host Drosophila melanogaster . In Congo, populations are less virulent against D. melanogaster but are able to develop successfully inside the tropical African species Drosophila yakuba . Host preferences are compared between two laboratory isofemale lines of L. boulardi , obtained from populations of Congo and Tunisia, respectively, and differing in virulence levels against D. melanogaster and D. yakuba . Host selection is studied by offering female parasitoids a choice between larvae of the two host species. In agreement with optimal foraging models, the line highly virulent against D. melanogaster shows a clear preference for this host species. The other line, less virulent against D. melanogaster but more virulent against D. yakuba , prefers to oviposit on D. yakuba . Such preferences can be observed after a period of host-patch exploitation only, suggesting that experience plays an important role in the host-selection process. These results evidence the existence of intraspecific variability in preference between two host species in L. boulardi , a major requisite in theoretical models of parasite specialization by the host. They also sustain the hypothesis that intraspecific variation in parasitoid preferences between host species might mirror intraspecific variation in virulence.     

Do beef cattle react consistently to different handling situations?

Beef cattle responses to handling depend partly on the genetic characteristics of the animals. However, the various methods used in order to assess these responses differ to a great extent. The purpose of this work is to study the relationship between two different situations extensively used to evaluate cattle reactions to handling. Moreover, the genetic variability of cattle responses to these two handling situations was investigated. Behavioural reactions of 245 Limousine heifers, from 10 sires, were evaluated both in a docility test and in a crush test. In the docility test, a human tried to lead and then to maintain the animal in the corner of a pen during 30 consecutive seconds, with a maximum duration of the test of 3.5min. A docility score summarised the animal's behavioural reactions to the test. The crush test procedure consisted of social isolation of the animal in a crush, with the head maintained in a head gate (5min), then exposure to a stationary human (30s), and finally stroking on the forehead (30s). An agitation index for each part of this test was computed from PCA analyses based on agitation behaviours. Sire effect was significant for every part of both tests (P<0.05). Heifers' behavioural responses to the docility test were significantly correlated with their responses to the crush test, when the animals were in isolation (r=0.29; P<0.001), when the human stood motionless in front of the animals (r=0.37; P<0.001), and when the human stroked them (r=0.28; P<0.001). Sires' behavioural reactions to the docility test (computed from their daughters' scores) were correlated with their reactions to the crush test only when the human was present, both when motionless (r=0.88; P<0.001) and when stroking the heifer (r=0.81; P<0.05). No relationship appeared between sires' behavioural reactions to the docility test and their responses to restraint in the crush when the human was absent (P=0.17). Furthermore, the crush test did not reveal the animals which presented aggressive reactions to handling in the docility test. The results exposed in this paper pointed out the existence of a general reactivity of beef cattle to handling, whether the animals are restrained or not, which appears influenced by the sire. Such reactivity is suggested to be mainly a consequence of the animals reactions to humans. The human environment needs to be precisely defined in the handling test procedures before using them as a selection criteria.     

Cl−, Na+, and H+ fluxes during the acidification of rabbit reticulocyte endocytic vesicles

The ionic fluxes associated with the ATP-dependent acidification of endocytic vesicles were studied in a preparation isolated from rabbit reticulocytes enriched for transferrin-transferrin receptor complexes. No vesicle acidification was observed in the absence of intra- and extravesicular ions (sucrose_in/sucrose_out), while maximal acidification was observed with NaCl_in/KCl_out·K _in ⁺ was a poor substitute for Na _in ⁺ , and Cl _out ^– could be replaced by other anions with the following efficacy of acidification: Cl^–>Br^–>I^–>PO ₄ ^3– >gluconate>SO ₄ ^2– . Flux studies using³⁶Cl^– and²²Na⁺ showed that the vesicles had a permeability for Cl^– and Na⁺, and that ATP-dependent H⁺ pumping was accompanied by a net influx of Cl^– and a net efflux of Na⁺ provided that there was a Na⁺ concentration gradient. After 3 mins, the time necessary to maximal acidification, the electrical charge generated by the entrance of H⁺ was countered to about 45% by the Cl^– influx and to about 42% by the Na⁺ efflux. These studies demonstrated that both Cl^– and Na⁺ fluxes are necessary for optimal endocytic vesicle acidification.     

Gas vesicles in actinomycetes?

Gas vesicles encoded by gvp genes provide buoyancy in many prokaryotes. In a recent Trends in Microbiology article entitled 'Gas vesicles in actinomycetes: old buoys in novel habitats?' van Keulen et al. documented the occurrence of gvp genes in soil-inhabiting actinomycetes but questioned whether any of them produce gas vesicles. We suggest that the protein encoded by gvpA in actinomycetes might be incompatible with the structure of the standard gas vesicle. Perhaps it has another role associated with the air-water interface.     

Salmonella entry into mammalian cells: different yet converging signal transduction pathways?

Salmonella bacteria have evolved means to subvert host cell signal transduction pathways to induce their uptake. Recently, progress has been made towards defining those pathways. Although it is clear that Salmonella evoke different signalling pathways in different cell lines, it is possible that these responses may be triggered by a common mechanism and that the diverse pathways may converge downstream in common effector molecules.