MRC OX-2 antigen: a lymphoid/neuronal membrane glycoprotein with a structure like a single immunoglobulin light chain.

The MRC OX-2 antigen is a rat cell surface glycoprotein of mol. wt. 41 000-47 000 found on neurones, thymocytes, B cells, follicular dendritic cells and endothelium. We now report the amino sequence for this antigen as deduced from the nucleotide sequence of cDNA clones detected by use of an oligonucleotide probe. The sequence contains 248 amino acid residues of which 202 residues are likely to be outside the cell with two domains that show homology with immunoglobulins. The N-terminal domain fits best with Ig V domains and Thy-1 antigen while the C-terminal part is like an Ig C domain. Thus the structure overall is similar to an Ig light chain or the T cell receptor beta chain. Three glycosylation sites are identified on each of the MRC OX-2 antigen domains.     

Effects of ischemia on VO2, tension, and vascular resistance in contracting canine skeletal muscle

This study examined the changes in O2 consumption (VO2), vascular resistance, and tension development during skeletal muscle contractions at reduced flow. We tested the hypothesis that when VO2 is limited by O2 supply, the skeletal muscle vasculature is not maximally dilated because of the fall in contractile force that accompanies the decrease in O2 supply. During 30 min of ischemic contractions, tension fell by 45 +/- 4% and VO2 fell 54 +/- 1% from preischemic levels. The O2 cost per unit tension did not change compared with nonischemic muscles. After the initial flow reduction, flow fell an additional 16 +/- 3% over 30 min. Adenosine infusion after 30 min of ischemic contractions increased flow by 42 +/- 3% but increased VO2 by only 9.8 +/- 2.3% and had no effect on tension development. When perfusion pressure was returned to normal after 30 min of ischemic contractions, twitch tension did not begin to recover within 20 min but tetanic tension showed a small improvement. VO2, although increased, remained well below the preischemic level. These results suggest that because of the reduced tension during ischemic contractions, the O2 supply-to-consumption ratio is nearly normal, which could explain the presence of the vasodilator reserve. The defect in tension development is long lived, producing a "stunned" muscle in which excess O2 supply does not restore function or VO2 to normal.     

Tryptophan Analog Resistance Mutations in Chlamydomonas Reinhardtii

Forty single gene mutations in Chlamydomonas reinhardtii were isolated based on resistance to the compound 5'-methyl anthranilic acid (5-MAA). In other organisms, 5-MAA is converted to 5'-methyltryptophan (5-MT) and 5-MT is a potent inhibitor of anthranilate synthase, which catalyzes the first committed step in tryptophan biosynthesis. The mutant strains fall into two phenotypic classes based on the rate of cell division in the absence of 5-MAA. Strains with class I mutations divide more slowly than wild-type cells. These 17 mutations map to seven loci, which are designated MAA1 to MAA7. Strains with class II mutations have generation times indistinguishable from wild-type cells, and 7 of these 23 mutations map to loci defined by class I mutations. The remainder of the class II mutations map to 9 other loci, which are designated MAA8-MAA16. The maa5-1 mutant strain excretes high levels of anthranilate and phenylalanine into the medium. In this strain, four enzymatic activities in the tryptophan biosynthetic pathway are increased at least twofold. These include the combined activities of anthranilate phosphoribosyl transferase, phosphoribosyl anthranilate isomerase, indoleglycerol phosphate synthetase and anthranilate synthase. The slow growth phenotypes of strains with class I mutations are not rescued by the addition of tryptophan, but the slow growth phenotype of the maa6-1 mutant strain is partially rescued by the addition of indole. The maa6-1 mutant strain excretes a fluorescent compound into the medium, and cell extracts have no combined anthranilate phosphoribosyl transferase, phosphoribosyl anthranilate isomerase and indoleglycerol phosphate synthetase activity. The MAA6 locus is likely to encode a tryptophan biosynthetic enzyme. None of the other class I mutations affected these enzyme activities. Based on the phenotypes of double mutant strains, epistatic relationships among the class I mutations have been determined.     

It's time to listen: there is much to be learned from the sounds of tropical ecosystems

Knowledge that can be gained from acoustic data collection in tropical ecosystems is low‐hanging fruit. There is every reason to record and with every day, there are fewer excuses not to do it. In recent years, the cost of acoustic recorders has decreased substantially (some can be purchased for under US$50, e.g., Hill et al. 2018) and the technology needed to store and analyze acoustic data is continuously improving (e.g., Corrada Bravo et al. 2017, Xie et al. 2017). Soundscape recordings provide a permanent record of a site at a given time and contain a wealth of invaluable and irreplaceable information. Although challenges remain, failure to collect acoustic data now in tropical ecosystems would represent a failure to future generations of tropical researchers and the citizens that benefit from ecological research. In this commentary, we (1) argue for the need to increase acoustic monitoring in tropical systems; (2) describe the types of research questions and conservation issues that can be addressed with passive acoustic monitoring (PAM) using both short‐ and long‐term data in terrestrial and freshwater habitats; and (3) present an initial plan for establishing a global repository of tropical recordings.     

Models for mating disruption by means of pheromone for insect pest control

Models are presented to investigate the population dynamic behavior of a pest population with the release of pheromone for mating disruption. Three mechanisms of mating disruption are considered: (i) confusion of males, (ii) competition with female pheromone trails yielding false trail following, (iii) emigration of males prior to mating. In addition, several refinements to confusion are considered. Confusion and emigration of males were found to be very similar both quantitatively and dynamically; also, a combination of both mechanisms was very little more efficient than either one separately. False trail following is difficult to compare with the other two, since competition with wild females is involved and thus the total population size enters the equations. Density dependence of the action of pheromones results in some cases in which mating disruption cannot control the pest population. Similarly, aggregation of the pest population decreases the efficiency of the method unless the pheromone action is density independent. Delayed mating of females makes control easier, and may constitute one mechanism for mating disruption.     

Role of CD4 epitopes outside the gp120-binding site during entry of human immunodeficiency virus type 1.

CD4 is the primary receptor for human immunodeficiency virus (HIV). The binding site for the surface glycoprotein of HIV type 1 (HIV-1), gp120, has been mapped to the C'-C" region of domain 1 of CD4. Previously, we have shown that a mutant of rat CD4, in which this region was exchanged for that of human CD4, is able to mediate infection of human cells by HIV-1, suggesting that essential interactions between HIV and CD4 are confined to this region. Our observations appeared to conflict with mutagenesis and antibody studies which implicate regions of CD4 outside the gp120-binding site in postbinding events during viral entry. In order to resolve this issue, we have utilized a panel of anti-rat CD4 monoclonal antibodies in conjunction with the rat-human chimeric CD4 to distinguish sequence-specific from steric effects. We find that several antibodies to rat CD4 inhibit HIV infection in cells expressing the chimeric CD4 and that this is probably due to steric hinderance. In addition, we demonstrate that replacement of the rat CDR3-like region with its human homolog does not increase the affinity of the rat-human chimeric CD4 for gp120 or affect the exposure of gp41 following binding to CD4, providing further evidence that this region does not play a crucial role during entry of virus.     

Immobilization of Burkholderia cepacia in polyurethane-based foams: embedding efficiency and effect on bacterial activity

Immobilization of the trichloroethylene-degrading bacterium Burkholderia cepacia was evaluated using hydrophilic polyurethane foam. The influence of several foam formulation parameters upon cell retention was examined. Surfactant type was a major determinant of retention; a lecithin-based compound retained more cells than pluronic- or silicone-based surfactants. Excessive amounts of surfactant led to increased washout of bacteria. Increasing the biomass concentration in the foam from 4.8 to 10.5% dry weight per wet weight of foam resulted in fewer cells being washed out. Embedding at reduced temperature did not significantly affect retention, while the use of a silane binding agent gave inconsistent results. The optimal formulation retained all but 0.2% of total embedded cells during passage of 2 L of water through columns containing 2 g of foam. All foam formulations tested reduced the culturability of embedded cells by several orders of magnitude, but O₂ consumption and CO₂ evolution rates of embedded cells were never less than 50% of those of free cells. Nutrient amendments stimulated an increase in cell volume and ribosomal activity in immobilized cells as indicated by hybridization studies using fluorescently labeled ribosomal probes. These results indicate that, although immobilized cells were mostly nonculturable, they were metabolically active and thus could be used for biodegradation of toxic compounds. Received 23 December 1996/ Accepted in revised form 13 March 1997     

Restriction-map variation associated with the G6PD polymorphism in natural populations of Drosophila melanogaster

Restriction-map variation was studied in 126 copies of the G6pd region in X chromosome lines of Drosophila melanogaster from North America, Europe, and Africa. Special attention was focused on the distribution of variation relative to the geographically variable polymorphism for two electrophoretic variants. Nucleotide heterozygosity as determined by eight six-cutter restriction enzymes for the 13-kb region is estimated, on the basis of the worldwide sample, to be 0.065%, which is the lowest value reported for any comparable region in the D. melanogaster genome. Significant linkage disequilibrium between electrophoretic alleles and restriction-site variation is observed for several sites. In contrast to published studies of other genetic regions, there are large insertions that reach significant frequencies and are found across considerable geographic distances. There is a clustering of this variation inside the first large intervening sequence of the G6PD gene.