IgM rheumatoid factor autoantibody and immunoglobulin-producing precursor cells in the bone marrow of humans

The natures of the IgM rheumatoid factor (RF)-, IgM-, and IgG-secreting cells in the human bone marrow as compared to the peripheral blood, have been investigated by (1) response to the polyclonal B-cell activator, the Epstein-Barr virus (EBV), (2) sensitivity to the S-phase specific antimetabolite hydroxyurea, (3) presence of the BA-1 and Ia antigens on the cell surface, and (4) cell size, as determined by counter flow elutriation. The EBV-inducible bone marrow IgM-RF precursors derived from medium to large B cells that were inhibited by hydroxyurea pretreatment. The marrow total IgM response derived from small to medium size cells, and was only partially inhibited by hydroxyurea. Hydroxyurea had no effect on IgM-RF or IgM synthesis by peripheral blood cells. These results indicate that the marrow EBV-induced IgM-RF response is not representative of the response by peripheral blood cells, moreover; the marrow RF secreting response arises from a dividing cell pool that may represent newly generated autoreactive B cells.     

The effect of nectar guides on pollinator preference: experimental studies with a montane herb

Summary Rare albino morphs of the montane larkspur Delphinium nelsonii differ from common blue-flowered morphs in overall flower color, and in the strength of a contrasting color pattern at the center of the flower that presumably guides pollinators to concealed nectar. Previous studies showed that bumblebees and hummingbirds discriminate against albinos when presented with mixtures of the 2 morphs, and that it takes these pollinators longer to fly between successive flowers on albino than on blue-flowered inflorescences. To explore the link between these observations, we measured pollinator preferences and flower-to-flower flight times (handling times) before and after painting flowers in 2 alternative ways that enhanced albino nectar guides. In all of 16 experimental replicates discrimination against albinos was reduced or eliminated after painting, and albino handling times declined toward values for blue-flowered inflorescences. This consistent result indicates that an inferior nectar guide increases the energetic cost of foraging at albinos. Increased cost in turn explains discrimination, under the reasonable assumption that hummingbirds and bumblebees are sensitive to foraging economics.     

Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism

Branched-chain amino acid metabolism in skeletal muscte promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation.     

Dependence of phytoplankton assimilation quotients on light and nitrogen source: implications for oceanic primary productivity

Photosynthetic production of oxygen by phytoplankton assemblagedominated by Peridinium in Lake Kinneret, Israel, generallyexceeds the molar equivalent rate of carbon assimilation. Carbonassimilation occurs only if oxygenic photosynthesis exceedsa light-dependent threshold. Assimilation quotients (mol C molO₂^–1) are a variable function of irradiance, and typicallyonly about one-half of the photoreductant produced during oxygenicphotosynthesis is used for reduction of carbon dioxide. Mostof the residual oxygenic photoreductant probably is used forlight-dependent reduction of nitrate, which competes with carbondioxide for oxygenic photoreductant. Nitrate is an importantsource of nitrogen for this algal assemblage, and light-dependentnitrate reduction probably is much larger than carbon dioxidereduction at lowest irradiances in the euphotic zone. Oxygenproduction also may be much larger than carbon assimilationat low light levels in other environments where oxidized formsof nitrogen are important nitrogenous nutrients for phytoplankton,as in the lower euphotic zone of the sea, where low rates ofcarbon assimilation by phytoplankton have been thought to beinconsistent with the amount of oxygen that accumulates duringsummer.     

Leghemoglobin-like sequences in the DNA of four actinorhizal plants

Summary A cloned cDNA partial copy of a soybean leghemoglobin mRNA was used to probe genomic DNA of four species of actinorhizal plants. Southern blot hybridization revealed the presence of sequences with homology to the leghemoglobin probe in DNA from Alnus glutinosa, Casuarina glauca, Ceanothus americanus and Elaeagnus pungens. The hybridization patterns of the restriction fragments revealed some fragment size conservation between the DNA of soybean and the DNA of four actinorhizal plants which are taxonomically unrelated to soybean or to each other. The results presented here indicate that globin gene sequences are much more widely distributed in the plant kingdom than has previously been thought. Furthermore, if sequence conservation is actually as high as the restriction fragment patterns suggest, the evolution of the DNA surrounding the globin sequences has been highly constrained.     

Restriction fragment polymorphisms as probes for plant diversity and their development as tools for applied plant breeding

Summary Maize and tomato cDNA clones have been hybridized in Southern blotting experiments to plant genomic DNA prepared from different lines to detect restriction fragment polymorphisms (RFPs). In maize we have found that a high degree of genetic variability is present, even among domestic inbred lines. Most randomly chosen maize cDNA clones can be used to detect elements of this variability. Similar levels of polymorphism are observed when genomic DNA is digested with any of a number of different restriction enzymes and probed with individual clones. When a clone is hybridized to genomic DNAs prepared from several different maize lines, a number of different alleles are often detected at a single locus. At the same time one clone can often detect more than one independently segregating locus by cross hybridization to related sequences at other loci. As expected these markers are inherited as simple codominant Mendelian alleles from one generation to the next and colinkage of these markers can be demonstrated in the progeny from a heterozygous parent. In similar studies with tomato, remarkably different results were found. Few RFPs were demonstrable among domestic Lycopersicon esculentum lines although a higher level of variability could be detected when comparing esculentum with its wild Lycopersicon relatives. These results are discussed in relation to the applied uses of RFPs in plant breeding as well as the inherent variability of different plant genomes.This work was supported in part by funds from Sandoz Ltd. (Basel, Switzerland) and its subsidiary company, Northrup King Co. (Minneapolis, Minn., U.S.A.) as well as by NSF SBIR grant #BSR-8360870.     

Interactions betweenAcyrthosiphon kondoi [Homoptera: Aphidoidea] andAphelinus asychis [Hymenoptera: Chalcidoidea] and other parasites and hosts

In laboratory trials to investigate the parasite/host spectra of certain aphid pests and hymenopterous parasites, the aphidAcyrthosiphon kondoi Shinji encapsulated the egg of the aphelinid parasiteAphelinus asychis Walker. The resultant brown, sclerotic capsule was formed within 24 h of exposure of the aphid to parasitization and as far as is known prevented the development of the parasite to the larval stage. The capsule remained throughout the life of the aphid, whose longevity and fecundity were apparently not seriously impaired. A small number ofAphelinus escaped encapsulation, especially in aphids already containing capsule(s), and developed into normal, reproductive adults.A. kondoi did not encapsulate, andA. asychis was not encapsulated by any other species. However, thoughA. asychis readily parasitizedAphis citricola van der Goot,A. nerii Boyer de Fonscolombe andToxoptera citricidus (Kirkaldy), most of its progeny ceased development in these aphids before reaching the mummification stage, and died within the dead or dying, non-mummified aphid host.     

Comparison of patterns of hybrid resistance to the BALB/c plasmacytomas LPC-1 and MPC-11

Summary Patterns of genetic control of hybrid resistance to the BALB/c plasmacytoma LPC-1 were studied for comparison with those to MPC-11, a plasmacytoma investigated previously. The overall patterns of hybrid resistance to the two tumors were similar, i.e., hybrids between BALB/c and BALB congenic resistant (CR) strains, A and A CR strains, SJL and DBA/2 were as susceptible to LPC-1 as BALB/c mice themselves, whereas hybrids between BALB/c and AKR, C57BL/Ks, DBA/1, C57BL/6 (B6), C57BL/10 (B10) and B10 CR strains were resistant to LPC-1 as previously shown with MPC-11. Heterozygosity within the H-2 complex alone was insufficient for resistance to either tumor. Among hybrids between BALB/c and the B10 CR strains, however, the presence of certain H-2 haplotypes influenced the degree of resistance seen and this H-2 effect was different for the two tumors. A sex effect on resistance to LPC-1, but not to MPC-11, was seen among F₁ hybrids between BALB/c and DBA/1 although not in any other F₁ hybrids. Among ((B10×BALB/c)F₁×BALB/c) and (BALB/c×(B10×BALB/c)F₁) and ((BALB/c×B10)F₁×BALB/c) and ((BALB/c×B10)F₁×BALB/c) backcross mice, however, significantly more males than females were resistant to LPC-1 and the results of this study are compatible with the idea that in F₁ hybrids between BALB/c and B10, resistance to LPC-1 is controlled by two dominant autosomal genes, one of which is sex-limited and neither of which is linked to H-2. In contrast, hybrid resistance to MPC-11 in this cross is controlled by a single gene. Cross-protection experiments indicated that the two tumors share at least one tumor-associated transplantation antigen.     

Identification of a deletion in the low density lipoprotein (LDL) receptor gene in a patient with familial hypercholesterolaemia

Summary DNA samples from 60 unrelated UK patients with familial hypercholesterolaemia (FH) were screened by Southern blot hybridisation to detect gross alterations in the low density lipoprotein (LDL) receptor gene. One patient was found to have a 2kb deletion in the 3 part of the gene. The deletion cosegregates with the FH phenotype in his family. This finding is compatible with the deletion being the cause of FH in this case and makes a presymptomatic test based on DNA analysis available for this family. The defects in most of the other patients are likely to be due to point mutations.