Comparative study of the milk fat globule membrane and the mouse mammary tumour virus prepared from the milk of an infected strain of Swiss albino mice.

Milk fat globule membranes and mammary tumour virus particles (d=1.17 g/cm3) have been obtained from the milk of a Swiss albino mice strain. Comparative biochemistry shows that these two structures differ significantly in the phospholipid, polypeptide and glycopolypeptide patterns and enzymatic activities. However, the lipid profile and the morphology of both structures suggest a filiation with the plasma membrane. Density fractions obtained from the crude virus preparation have been thoroughly investigated. The results suggest that most of these fractions represent degraded virus and/or atypical virus assembly.     

The dipeptide repeat region of the fibrinogen-binding protein (clumping factor) is required for functional expression of the fibrinogen-binding domain on the Staphylococcus aureus cell surface

Clumping factor of Staphylococcus aureus is a fibrinogen-binding protein that is located on the bacterial cell surface. The protein has an unusual repeat domain (region R) comprising mainly the dipeptide aspartate and serine. To determine if region R has a role in the surface display of the fibrinogen-binding region A domain, deletions lacking the region R encoding region of the clfA gene were generated. To determine the minimum length of region R required for wild-type levels of ClfA expression, variants with truncated region R domains were constructed. S. aureus cells expressing mutated clfA genes were tested for (i) proteins released by lysostaphin treatment that reacted with antisera specific for region A, (ii) clumping in soluble fibrinogen, (iii) adherence to immobilized fibrinogen and (iv) expression of the ClfA antigen on the cell surface by fluorescent activated cell sorting analysis. Each construct expressed three major immunoreactive proteins, two of which were putative N-terminal degradation products. Region R residues greater than 40 were required between region A and W (72 residues between region A and the LPDTG sorting signal) for wild-type levels of clumping in fibrinogen. A stepwise decrease in clumping titre was observed as the distance between region A and LPDTG was decreased from 72 to 4 residues. Similarly, a decrease in binding of anti-ClfA serum and in binding to fibrinogen-coated plastic surfaces was observed with cells expressing ClfA with 40 region R residues or less. Nevertheless, low levels of adherence to fibrinogen and binding to anti-ClfA serum occurred with ClfA derivatives that lacked region R altogether. This indicates that a small proportion of the ClfA molecules are linked to peptidoglycan very close to the cell surface but that residues greater than 72 are needed to allow sufficient ClfA molecules to span the entire cell wall and to display the biologically active A domain in a form that can participate fully in fibrinogen binding.     

Effects of dietary manipulations and glucose infusion on glucagon response during exercise in rats

Tadjoré, Maurice, Raynald Bergeron, Martin Latour,François Désy, Claude Warren, and Jean-Marc Lavoie.Effects of dietary manipulations and glucose infusion on glucagonresponse during exercise in rats. J. Appl.Physiol. 83(1): 148-152, 1997.The purpose of thepresent investigation was to test the hypothesis that blood glucoseconcentration is not always related to glucagon response duringexercise. Three groups of rats were submitted to a prolonged (3-h)swimming exercise. Two groups of rats had their normal food intakerestricted by 50% the night before the experiment. One of these twogroups of rats was intravenously infused with glucose throughoutexercise to maintain euglycemia. The third group of rats swam whileunder normal dietary conditions. Plasma glucose, sampled in arterialblood, was reduced (P < 0.05) at 75, 105, 150, and 170 min of exercise (from ~130 to 110 mg/dl) in thefood-restricted animals without glucose infusion, whereas a significant(P < 0.05) increase was measured inthe two other groups during exercise. A significant(P < 0.01) difference in the meanintegrated areas under the glucose-concentration curve was found onlybetween the fed and the two food-restricted groups. Plasma insulinconcentrations decreased (P < 0.05)similarly in all groups during exercise, whereas plasma epinephrine andnorepinephrine concentrations increased significantly(P < 0.01) in all groups. Despitedifferences between groups in plasma glucose response during exercise,and despite the absence of any decrease in exercising blood glucoselevels in at least two of the three groups, plasma glucagon responseswere increased (P < 0.05) similarlyin all groups (from ~250 to 550 pg/ml) at the end of the exerciseperiod. The increase in glucagon was significant after 90 min ofexercise in the food-restricted groups, with or without glucoseinfusion, but only after 140 min in the fed group. These resultsindicate that the glucagon response during exercise is not alwayslinked to the decrease in plasma glucose.

     

Dynamics of female choice for parental care in a fish species where care is facultative

In the peacock wrasse (Symphodus tinca), females either placetheir eggs in a nest under the care of a male or disperse theireggs widely so that they receive no protection. The same femalecan spawn in both modes. Females appear to prefer males withnests early in the nesting cycle, and they spawn less oftenthan expected in late-cycle nests and with non-nesting males.Survival and hatching success are consistently higher for eggsplaced in early nests, particularly in mid-season when egg predationis intense and hatching times are relatively long. Nevertheless,30%-80% of females place their eggs outside nests, even whenhatching success is more than four times greater with care.A model incorporating search time for nests correctly predictedthe qualitative changes in the tendency of females to choosecare or no care over the course of the mating season. Extensionsof the model suggest that in the early part of the season, whennests are rare and the relative survival advantage of parentalcare is small, females should sample no more than one nest beforeopting for no care. In mid-season, when the advantages of careare highest and between-nest travel times are low, females areestimated to visit at least 8 nests before abandoning the effort,corresponding to a giving-up time of about 43 min of search.Later in the season, when short hatching times reduce the relativebenefit of care, females are estimated to visit between 4 and5 nests before giving up, corresponding to about 31 min of search.We suggest that the variability in parental care in this speciesarises from seasonal changes in relative costs and benefitsof care for the two sexes.     

Direct selective techniques for the isolation of pyrimidine auxotrophs in yeast

Summary Selective techniques have been developed to obtain auxotrophic mutants in four of the five loci controlling the enzymes involved in Yeast pyrimidine biosynthesis. These loci are thus available for mutagenic studies requiring numerous forward as well as backward mutations.     

Non-Mendelian Mutation Allowing Ureidosuccinic Acid Uptake in Yeast

Mutants of Saccharomyces cerevisiae capable of growth on a minimal medium supplemented with ureidosuccinic and glutamic acids have been isolated from a pyrimidineless strain. One of these mutants consistently yielded a non-Mendelian meiotic segregation. Moreover, the mitotic transmission of the mutation was very high. It is suggested that the mutation is nonchromosomal and could be mitochondrial. However, this mutation behaves very differently from other mitochondrial mutations.     

Self-pollination,style length development and seed set in self-compatible Asteraceae: evidence from Senecio vulgaris L.

Background: Variation in style length has been reported in Senecio vulgaris and has been associated with outcrossing rate.

Aims: To determine if (i) long styles lack germinated pollen on stigmas left to self-pollinate, (ii) successful self-pollination causes styles to stop elongating and shrink in length and (iii) seed set increases with the amount of pollen deposited on stigmas.

Methods: Determined germinated self-pollen on stigmas of long and short styles after auto-self-pollination; scored style length over 48 h in self-pollinated and non-pollinated florets; recorded seed set after placing different amounts of pollen on stigmas.

Results: Most long-styled florets had zero or low amounts of germinated pollen on stigmas in contrast to most short-styled florets. Styles initially elongated to the same length in self-pollinated and non-pollinated florets, then shrank in length in self-pollinated florets while continuing to elongate in non-pollinated florets. Seed set increased with number of pollen grains deposited on stigmas.

Conclusions: Successful self-pollen deposition and/or germination on stigmas of S. vulgaris are indicated by presence of short styles, whereas the opposite is indicated by presence of long styles in florets left to self-pollinate. Self-pollination causes styles to shrink after initially elongating. Seed set is dependent on the amount of pollen deposited on stigmas.     

Conserving a variety of ancient forest patches maintains historic arthropod diversity

Forests are naturally extensive tracts. However, in South Africa natural fires over many millennia have reduced forested areas into small remnants spread throughout a grassland matrix. Small patches, especially distant patches, are generally considered to be adverse for forest specialists, owing to decreased forest interior and increased edge. Here we test this assumption by determining the impact of forest interpatch distance and patch size on epigaeic arthropod diversity in this globally rare vegetation type. Forty patches were selected: ten large (100–435 m diameter) that are distant (500–645 m) from other patches, ten large that are close to other patches (38–97 m), ten small (30–42 m) that are distant, and ten small-close patches. Each patch had two plots: edge and interior. Arthropods were sampled using pitfall traps, Berlese-Tullgren funnels and active searches. Interiors and edges had similar species richness and composition, excluding spiders, which were richer in interiors. Patch size significantly influenced species richness of predatory beetles and arthropod assemblages, excluding spiders. Effect of the interaction between patch size and interpatch distance on species richness and composition varied among taxa. Furthermore, large patches supported similar assemblages regardless of interpatch distance. Arthropod response, particularly ants to patch size and interpatch distance, was partly shaped by the matrix type. The percentage of surrounding grassland had little effect on arthropod diversity. We can conclude that large and close patches are important for arthropod conservation. Nevertheless, it is also important to conserve a variety of patch sizes at various distances to maximize overall arthropod composition.     

Massively parallel sequencing of single cells by epicPCR links functional genes with phylogenetic markers

Many microbial communities are characterized by high genetic diversity. 16S ribosomal RNA sequencing can determine community members, and metagenomics can determine the functional diversity, but resolving the functional role of individual cells in high throughput remains an unsolved challenge. Here, we describe epicPCR (Emulsion, Paired Isolation and Concatenation PCR), a new technique that links functional genes and phylogenetic markers in uncultured single cells, providing a throughput of hundreds of thousands of cells with costs comparable to one genomic library preparation. We demonstrate the utility of our technique in a natural environment by profiling a sulfate-reducing community in a freshwater lake, revealing both known sulfate reducers and discovering new putative sulfate reducers. Our method is adaptable to any conserved genetic trait and translates genetic associations from diverse microbial samples into a sequencing library that answers targeted ecological questions. Potential applications include identifying functional community members, tracing horizontal gene transfer networks and mapping ecological interactions between microbial cells.