Isolation of anucleate cells using a fluorescence activated cell sorter (FACS II)

Human fibroblasts or mouse teratocarcinoma cells were enucleated by density gradient centrifugation in the presence of cytochalasin B (CB). The resulting mixed population of nucleated and anucleate cells was further purified by flow sorting, using the dye Hoechst 33342 as a fluorescent label for the nucleated cells. The purity of the anucleate cells obtained with this technique was at least 99%, as was shown by histological staining of the sorted fractions. Sorted enucleated fibroblasts were shown to have an intact cell membrane as indicated by their ability to convert fluorescein diacetate into fluorescein and to accumulate this product. They were found to attach and spread when cultured and showed protein synthesis immediately after enucleation, evidenced by the incorporation of [³H]leucine. Sorted enucleated teratocarcinoma cells also had an intact cell membrane, but they did not attach when cultured.     

'Receptor-independent' infection of Mu G(−) phage in Escherichia coli K-12

Abstract Bacteriophage Mu with its invertible G segment in G(−) orientation does not make plaques on Escherichia coli K-12, due to the absence of a suitable lipopolysaccharide receptor. Plaques formed by Mu G(−) were found, however, when the infected E. coli K-12 strain harbours a plasmid with the cloned DNA inversion function Gin which converts the infecting G(−) phage to G(+). Under overproducing conditions, where Gin expression is placed under the control of the tac promoter, the infectivity of Mu G(−) can be estimated as approximately 1% of that in the presence of the receptor. Furthermore, interaction of Mu G(−) with the E. coli K-12 cell wall leads to interference with the plating of a Mu G(+) variant which has the new phenotype Pen⁻ (penetration-negative).     

Transforming growth factor-beta (TGF beta) is chemotactic for human monocytes and induces their expression of angiogenic activity

TGF beta stimulates human blood monocyte migration, with peak migratory response occurring consistently at a concentration of 16-100 fg/ml. Checkerboard analysis revealed both chemotactic and chemokinetic components to this response. At higher concentrations (10-100 pg/ml), TGF beta stimulated expression of angiogenic activity by monocytes. While mRNA for TNF alpha was undetectable in resting monocytes, high steady state levels of TNF alpha mRNA were rapidly induced in TGF beta-treated monocytes. TGF beta is secreted by a number of neoplastic cells as well as normal cells such as platelets and lymphocytes. TGF beta may recruit monocytes from the circulation, and subsequently activate them to express angiogenic activities such as TNF alpha, thus playing an important role in wound repair, inflammation and tumor growth.     

A comparative fluorescence polarization study of cis-parinaroyl-phosphatidylcholine and diphenylhexatriene in membranes containing different amounts of cholesterol

The steady state fluorescence anisotropy (rs) of 1-acyl-2-cis parinaroyl phosphatidylcholine (PnPC) was compared with that of diphenylhexatriene (DPH) in a variety of model- and biological membrane systems. The fluorescence anisotropy of both probes responded similarly to temperature changes and variations in the acyl chain composition in phosphatidylcholine (PC) liposomes. The presence of proteins and cholesterol increased rs for both DPH and PnPC in the biological membranes as compared to the isolated polar membrane lipids. Comparison of DPH and PnPC in dipalmitoyl-PC-liposomes with and without 50 mol% cholesterol, showed at temperatures above the phase transition of pure dipalmitoyl-PC the presence of cholesterol increased the rs-value for DPH strongly, whereas the rs-value for PnPC was much less affected. In the cholesterol-rich erythrocyte membrane as well as in microsomes from Morris hepatoma 7787, which have an increased cholesterol content as compared to normal rat liver microsomes, the rs of DPH was higher than that of PnPC. No large differences between the rs-values of both probes were evident in the normal cholesterol-poor rat liver microsomes. These effects are discussed in terms of structural differences between the probes and variation of cholesterol content. Alterations in the fatty acid composition of PC present in human erythrocyte membranes were introduced with the aid of a PC-specific transfer protein. Fluorescence anisotropy values of both probes hardly changed upon enrichment of the red cell membrane with either dipalmitoyl PC or 1-palmitoyl-2-arachidonyl PC.     

Social insects with memory

The paper presents a mathematical model to investigate the collective behaviour of an ant colony when memory of the ants interferes with the usual interaction between individuals. The approach is developed in the framework of a simple situation consisting in tandem recruitment in a population of conservative ants, but it is susceptible to be applied also to a wider range of problems. The principle of the method is inspired by the work of Leuth?usser and Tarazona who developed the correspondence between a model for macromolecular time evolution and the equilibrium statistical mechanics of a higher-dimensional Ising system. Received: 18 March 1997 / Accepted in revised form: 30 July 1997