A stochastic model of a temperature-dependent population

The theoretical basis is developed for a population model which allows the use of constant temperature experimental data in predicting the size of an insect population for any variable temperature environment. The model is based on a stochastic analysis of an insect's mortality, development, and reproduction response to temperature. The key concept in the model is the utilization of a physiological time scale. Different temperatures affect the population by increasing an individual's physiological age by differing rates. Conditions for the temperature response properties are given which establish the validity of the model for variable temperature regimes. These conditions refer to the relationship between chronological and physiological age. Reasonable agreement between the model and field populations demonstrates the practicality of this approach.     

Genetic induction of bivalent interlocking in common wheat

The frequency of interlocking bivalents at first meiotic metaphase of common wheat Triticum aestivum L., which is normally very low, is significantly increased by raising the dosage (from two to three, four and six) of the Ph1 gene, located on the long arm of chromosome 5B (5BL). In several cells more than three bivalents were interlocked in one chain configuration indicating involvement of non-homoeologous bivalents. Plants with reduced dose (one or zero) of Ph1 also exhibited an increased frequency of interlocking but to a lesser extent than those with high gene dosage. However, chains of more than three interlocked bivalents were never observed in these plants, suggesting that with one or zero doses of Ph1 interlocking is restricted to homoeologous bivalents only. Chromosomal arm 5BS affected interlocking in an opposite manner to 5BL; namely, two and four doses of 5BS markedly reduced interlocking frequency. The modification in the frequency of interlocking bivalents by these genetic manipulations represents the first successful attempt to affect interlocking by genetic means. The results are explained on the basis of the hypothesis that this gene system controls somatic and premeiotic association of both homologous and homoeologous chromosomes.     

An ordered arrangement of chromosomes in the somatic nucleus of common wheat Triticum aestivum L.

Spatial relationships between chromosomes of the same genome, both homologous and non-homologous, were studied in root-tip cells of common wheat, Triticum aestivum (2n = 6x = 42). Mean distance between members of all the 21 homologous pairs (seven in each of the three genomes) and of 45 out of the 63 possible non-homologous combinations of two (21 in each genome) were determined. To minimize disruption of nuclear chromosomal arrangement, the cells were pretreated with cold temperature either in tap water or in a physiological medium (White solution) and distances between cytologically marked chromosomes were measured at metaphase. Comparison of distances for homologues with those for non-homologues indicated clearly that, within each genome, the homologous chromosomes were significantly closer to one another than were the non-homologues. Distances between homologues were similar in all three genomes, as were distances between non-homologues. The data are consistent with the hypothesis that the chromosomes of each genome of common wheat are arranged in the somatic nucleus in a highly specific ordered pattern. In this hypothetical arrangement, homologous chromosomes are closely associated, while the nonhomologues occupy definite positions with respect to one another. The universality of the phenomenon and its cellular mechanism and biological significance are discussed.     

Control of phosphatidylcholine synthesis in Hep G2 cells. Effect of fatty acids on the activity and immunoreactive content of choline phosphate cytidylyltransferase.

We examined the effect of fatty acids on phosphatidylcholine synthesis and cytidylyltransferase activity in Hep G2 cells. Treatment of Hep G2 cells with oleic acid caused an increase in the incorporation of [methyl-14C]choline into phosphatidylcholine and a corresponding decrease in radioactivity in choline phosphate using a pulse-chase procedure. This result is consistent with a fatty acid-induced increase in the cytidylyl-transferase step in the choline pathway. We measured cytidylyltransferase activity in membrane fractions and in cytosol (100,000 x g supernatant or soluble enzyme released by digitonin). The activity increased in both membrane and cytosol. Thus, an increase in total activity occurred. Cytidylyltransferase protein determined by Western blot immunoassay increased after oleic acid treatment. Immunotitration of cytidylyltransferase protein also indicated that an increase in enzyme protein resulted from oleic acid treatment. Cycloheximide did not prevent the oleic acid-induced increase in cytidylyltransferase activity. The increase in enzyme activity was apparent when we measured the activity in the presence or absence of lipid activators. Separation of cytosolic cytidylyltransferase into H- and L-forms showed that the increase in cytosolic activity was due to an increase in H-form. The amount of L-form did not change. We interpret these results to suggest that fatty acid treatment of Hep G2 cells promoted the formation of active cytidylyltransferase (H-form) from a preexisting inactive form. The increased activity was distributed between membranes and the lipoprotein form in cytosol (H-form).     

Lewontin and Kojima Meet Fisher: Linkage in a Symmetric Model of Sex Determination

The effect of linkage and epistasis on the evolution of the sex-ratio is studied in a symmetric two-locus model of autosomal sex determination closely related to the symmetric viability model of R. C. Lewontin and K. Kojima. R. A. Fisher's expectation of an even sex ratio for autosomal sex determination by a single gene governs the dynamics when the loci are tightly linked. However, recombination may preclude optimization of the sex ratio just as occurs in viability selection models. Many of the evolutionary phenomena known for the symmetric viability model also occur here. In addition, we exhibit a series of new phenomena related to the presence of surfaces of even sex ratio.     

Suppression of bacterial cell wall-induced polyarthritis by recombinant gamma interferon

Group A streptococcal cell wall fragments (SCW) induce erosive polyarthritis, characterized by synovial cell hyperplasia and intense mononuclear cell infiltration, in susceptible rats. Because of the known antiproliferative and immunomodulatory effects of interferon (IFN), we evaluated the effect of systemically administered alpha, beta and gamma IFN on the evolution of these destructive lesions. Treatment with gamma IFN not only reduced the acute response, but had an even greater suppressive effect on the chronic mononuclear cell-mediated destructive phase of the disease (articular index 10.2 +/- 1.2 for SCW only versus 3.8 +/- 0.7 for SCW + gamma IFN; p less than 0.01). Treatment with gamma IFN was more effective in the suppression of the arthritis than alpha, beta IFN. Histopathologic evaluation of the joints demonstrated that gamma IFN-treated animals had significantly fewer inflammatory cells, and less synovial hyperplasia and erosions than the SCW controls. gamma IFN suppression of mononuclear cell prostaglandin synthesis and synovial fibroblast proliferation was consistent with its anti-arthritic effects. These data indicate that the pathophysiology of SCW-induced erosive polyarthritis is subject to regulatory control by gamma IFN and that the mechanisms of suppression may be relevant in the treatment of rheumatoid arthritis.     

A sensitive method for the detection of beta-galactosidase in transfected mammalian cells.

A sensitive method has been developed for the detection of E. coli beta-galactosidase in transfected HeLa cells. The chromogenic substrate, CPRG (chlorophenol red-beta-D-galactopyranoside), was compared with ONPG (o-nitrophenyl-beta-D-galactopyranoside) by kinetic analysis with purified beta-galactosidase. The Km for CPRG was 1.35 mM and the Vmax was 21.4, whereas the Km for ONPG was 2.42 and the Vmax was 41.1. CPRG at 8.0 mM (6-fold Km) gave 86% of the Vmax and was used as the standard concentration for quantitation of enzyme levels. The Vmax for CPRG was half that for ONPG, and chlorophenol red has an extinction coefficient that is 21-fold higher than o-nitrophenol; these factors make CPRG about 10-fold greater in sensitivity for the quantitation of enzyme levels. The use of Nonidet P-40 to lyse the cells and the use of CPRG as substrate permitted the rapid detection of low levels of enzyme production from transfected human cells that could not be detected using ONPG.     

Purification and characterization of the bombesin/gastrin-releasing peptide receptor from Swiss 3T3 cells

The bombesin/gastrin-releasing peptide (GRP) receptor was solubilized from Swiss mouse 3T3 cell membranes in an active form and was purified about 90,000-fold to near homogeneity by a combination of wheat germ agglutinin-agarose and ligand affinity chromatography. The purified receptor displayed a single diffuse band with a Mr of 75,000-100,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After treatment of the receptor with N-glycanase, removing N-linked oligosaccharide moieties, the protein yielded a Mr = 38,000 band. These results agree with the Mr value estimated for the GRP receptor that was labeled on Swiss 3T3 cells by cross-linking to 125I-GRP1-27. GRP1-27 bound to the purified receptor with a Kd of 0.038 +/- 0.019 nM. By comparison, the soluble receptor in unfractionated extracts and intact membranes displayed a Kd for GRP1-27 of 0.036 +/- 0.003 nM and 0.13 +/- 0.04 nM, respectively. The relative potencies of a series of GRP analogs for the soluble receptor and intact membranes indicated that the extraction procedure did not significantly alter the receptor's ligand binding specificity. However coupling of the receptor to its guanyl nucleotide regulatory protein was not maintained in the soluble extract, and a G-protein did not co-purify with the receptor. Physiological concentrations of NaCl greatly inhibited the binding of some GRP analogs to the receptor, while the binding of other analogs was not affected. A domain on the GRP molecule involving Lys-13 or Arg-17 was identified which promoted binding to the GRP receptor under conditions of low ionic strength. These findings aided the development of an effective ligand affinity resin for the purification of the GRP receptor.     

Electrochemical cells for voltammetry, coulometry, and protein activity assays of small-volume biological samples

Cell designs, experimental protocols, and results for electrochemical investigation of small quantitites of biological materials under anaerobic conditions are reported. Three types of electrochemical experiments are considered: (i) cyclic voltammetry of 20- to 100-microliters samples; (ii) direct coulometry of 0.5- to 1.5-ml samples; and (iii) an electrochemically initiated protein activity assay which includes provision for analysis of gaseous reaction products and correlation with electron flux. The first two procedures are illustrated by measurement of the formal electrode potential (E0') and number of electrons transferred (n) in redox reactions of small quantities of biological and inorganic materials. The third procedure is illustrated by assaying the activity of the MoFe protein plus Fe protein complex from Azotobacter vinelandii nitrogenase for reduction of C2H2 to C2H4.