Protective effects of differentiation inducers on natural killer sensitivity of K 562 cells: Analysis at a single-cell level

K 562 cells induced to differentiate by sodium butyrate (SB) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were studied for their capacities to be bound and killed by large granular lymphocytes (LGL) in a single-cell cytotoxicity assay in agarose. After SB treatment, K 562 cells were less efficient in binding to LGL, whereas the frequency of killer cells among bound LGL was unaffected. When TPA was used to induce K 562 differentiation, the binding of LGL to their target and the lytic efficiency of the bound LGL were both diminished when compared to control K 562 cells. It has been demonstrated that the expression of structures involved in the binding of natural killer (NK) effectors to their targets could be correlated with the target-differentiation stage. It is shown that phorbol-ester treatment can also affect NK target structures involved in the killing step.     

Drug action against intracellularly growingMycobacterium xenopi

The intracellular growth kinetics ofMycobacterium xenopi was studied in the murine J-774 macrophage cell line model. During the initial 4 days of infection, the bacilli divided about every 33 h. Electron microscopy of infected macrophages showed that bacteria inside phagosomes were surrounded by a protective electron-transparent zone (ETZ). This model was used for comparing the extracellular and intracellular activities of the following drugs: pristinamycin (PRISTINA), isoniazid (INH), clofazimine (CLOFA), rifabutin (=ansamycin; ANSA), rifampicine (RIFA), streptomycin (SM), ethambutol (EMB), and five fluoroquinolones, namely, ciprofloxacin (CIPRO), ofloxacin (OFLO), pefloxacin (PEFLO), enoxacin (ENOX) and norfloxacin (NORFLO). All the drugs were tested within their obtainable serum level concentrations in man. Under these conditions, CLOFA, SM, CIPRO, and OFLO were highly active against intracellularly growingM. xenopi, INH and RIFA were moderately active, whereas ANSA, PRISTINA, EMB, PEFLO, ENOX, and NORFLO were only growth inhibiting. The comparison of these data with extracellular activities of the same drugs underlined the discrepancies observed in test-tube drug activity evaluation and its correlation with results of chemotherapy in patients in whom the drug has essentially an intracellular bacterial killing role.     

The origin of kinetic cooperativity in prehiotic catalysts

A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C₁₂) may be able to catalyze the hydrolysis ofN-carbobenzoxy-l-alaninep-nitrophenyl ester (N-Cbz-Ala) as well asp-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state. After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis ofp-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate. Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst. When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady state to occur. This is precisely what takes place with N-Cbz-Ala. A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot follow classical Michaelis-Menten kinetics and displays positive cooperativity. It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze. Correspondence to: J. Ricard     

Production of flavor esters by lipases of Staphylococcus warneri and Staphylococcus xylosus

The present paper describes the potential of Staphylococcus warneri and Staphylococcus xylosus lipases in the production of a variety of flavor esters. Both immobilized lipases produced ethyl esters from hexanoic to oleic acids with an optimum at decanoic acid. They esterified aliphatic and branched chain primary alcohols from ethanol to hexanol. Under our standard conditions, acetic, butyric, 2-methyl butyric, 3-methyl butyric, and valeric acids underwent slight esterification.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

The Second Messenger, Cyclic AMP, Is Not Sufficient for Myelin Gene Induction in the Peripheral Nervous System

Abstract: The adenylyl cyclase-cyclic AMP (cAMP) second messenger pathway has been proposed to regulate myelin gene expression; however, a clear correlation between endogenous cAMP levels and myelin-specific mRNA levels has never been demonstrated during the induction or maintenance of differentiation by the myelinating Schwann cell. Endogenous cAMP levels decreased to 8–10% of normal nerve by 3 days after crush or permanent transection injury of adult rat sciatic nerve. Whereas levels remained low after transection injury, cAMP levels reached only 27% of the normal values by 35 days after crush injury. Because P₀ mRNA levels were 60% of normal levels by 14 days and 100% by 21 days after crush injury, cAMP increased only well after P₀ gene induction. cAMP, therefore, does not appear to trigger myelin gene induction but may be involved in myelin assembly or maintenance. Forskolin, an activator of adenylyl cyclase, increased endoneurial cAMP levels only in the normal nerve, and in the crushed nerve beginning at 16 days after injury, but at no time in the transected nerve. Only by treating transected nerve with 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cAMP phosphodiesterases, in combination with forskolin was it possible to increase cAMP levels. No induction of myelin genes, however, was observed with short- or long-term treatment with IBMX and forskolin in the transected nerve. A three-fold increase in phosphodiesterase activity was observed at 35 days after both injuries, and a nonmyelinated nerve was shown to have even higher activity. These experiments, therefore, suggest an important role for phosphodiesterase in the inactivation of this second messenger-dependent stimuli when Schwann cells are non-myelinating, such as after sciatic nerve injury or in the nonmyelinated nerve, which again implies that cAMP may be required for the maintenance of the myelin sheath.