Oviposition strategies, host coercion and the stable exploitation of figs by wasps

A classic example of a mutualism is the one between fig plants (Ficus) and their specialized and obligate pollinating wasps. The wasps deposit eggs in fig ovules, which the larvae then consume. Because the wasps derive their fitness only from consumed seeds, this mutualism can persist only if the wasps are prevented from laying eggs in all ovules. The search for mechanisms that can limit oviposition and stabilize the wasp-seed conflict has spanned more than three decades. We use a simple foraging model, parameterized with data from two Ficus species, to show how fig morphology reduces oviposition rates and helps to resolve the wasp-seed conflict. We also propose additional mechanisms, based on known aspects of fig biology, which can prevent even large numbers of wasps from ovipositing in all ovules. It has been suggested that in mutualistic symbioses, the partner that controls the physical resources, in this case Ficus, ultimately controls the rate at which hosts are converted to visitors, regardless of relative evolutionary rates. Our approach provides a mechanistic implementation of this idea, with potential applications to other mutualisms and to theories of virulence.     

Downregulation of ENaC activity and expression by TNF-alpha in alveolar epithelial cells

Sodium absorption by an amiloride-sensitive channel is the main driving force of lung liquid clearance at birth and lung edema clearance in adulthood. In this study, we tested whether tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine involved in several lung pathologies, could modulate sodium absorption in cultured alveolar epithelial cells. We found that TNF-alpha decreased the expression of the alpha-, beta-, and gamma-subunits of epithelial sodium channel (ENaC) mRNA to 36, 43, and 16% of the controls after 24-h treatment and reduced to 50% the amount of alpha-ENaC protein in these cells. There was no impact, however, on alpha(1) and beta(1) Na(+)-K(+)-ATPase mRNA expression. Amiloride-sensitive current and ouabain-sensitive Rb(+) uptake were reduced, respectively, to 28 and 39% of the controls. A strong correlation was found at different TNF-alpha concentrations between the decrease of amiloride-sensitive current and alpha-ENaC mRNA expression. All these data show that TNF-alpha, a proinflammatory cytokine present during lung infection, has a profound influence on the capacity of alveolar epithelial cells to transport sodium.     

Antigenicity of recombinant proteins after regioselective immobilization onto polyanhydride-based copolymers

We previously demonstrated that the introduction of a tag consisting of several contiguous lysines at the N- or C-terminus of a recombinant protein greatly improved the covalent grafting of the protein onto negatively charged maleic anhydride-alt-methyl vinyl ether (MAMVE) copolymer, under many different experimental conditions (Ladavière, C., et al. (1998) Bioconjugate Chem. 9, 655; Allard, L., et al. (2002) Biotechnol. Bioeng. 80, 341). The grafting efficiency was dependent on the charge and amine density of the tag, characteristics which were determined by the tag composition. The six lysine tag (Lys6) was found to be the most efficient (Allard, L., et al. (2001) Bioconjugate Chem. 12, 972). In the present work, the biological activity of Lys6-proteins covalently bound to polymer was investigated. N- or C-terminal Lys6-tagged HIV-1 p24 recombinant proteins (RK24H and RH24K) were grafted onto MAMVE, and the antigenicity each of the bioconjugates was evaluated using six monoclonal antibodies that recognized different epitopes distributed along the protein. We demonstrate that the position of the tag and the hydrolysis rate of the anhydride moieties of the polymer are the two main parameters involved in the conservation of the biological activity of the immobilized protein. We thus present a process which allows an efficient oriented immobilization of proteins onto copolymers with optimal biological activity that is suitable for the controlled production of active bioconjugates.     

Monoubiquitination and endocytosis direct gamma-secretase cleavage of activated Notch receptor

Activation of mammalian Notch receptor by its ligands induces TNFalpha-converting enzyme-dependent ectodomain shedding, followed by intramembrane proteolysis due to presenilin (PS)-dependent gamma-secretase activity. Here, we demonstrate that a new modification, a monoubiquitination, as well as clathrin-dependent endocytosis, is required for gamma-secretase processing of a constitutively active Notch derivative, DeltaE, which mimics the TNFalpha-converting enzyme-processing product. PS interacts with this modified form of DeltaE, DeltaEu. We identified the lysine residue targeted by the monoubiquitination event and confirmed its importance for activation of Notch receptor by its ligand, Delta-like 1. We propose a new model where monoubiquitination and endocytosis of Notch are a prerequisite for its PS-dependent cleavage, and discuss its relevance for other gamma-secretase substrates.     

Again on language of biology]

Some time ago I proposed in an Editorial in this journal some considerations on the language of biology. I concluded that, to realize an autonomy of such a language (and therefore of biology), we have to develop a valid language for biology. In such a context, it seemed to me that the term "metaphors" referred to the concepts concerning the information carried by genetic code, was a reasonable one. However, Barbieri's article in this issue of Rivista di Biologia / Biology Forum calls for a reply. Of course, we do not know very much in this field, even if we have some evidence that a sequence of bases on a DNA is not determined only by chance. In any case we can exclude that nature in this occasion has "invented" a code. Nature doesn't "invent" anything: it only follows its rules, that we name "laws of nature". Barbieri quotes the Morse code, but forgets to say that such a code is "conventional" in the sense that it is valid only because it is the result of an "agreement" between Morse and the users of that code. There is nothing more unnatural than a "code": with whom nature should actually have to "reach an agreement"? As a matter of fact, we interpret as "information" what happens by law of nature. Also Barbieri's thesis that genes and proteins are molecular artifacts, assembled by external agents, whereas generally molecules are determined by their bonds, i.e. by internal factors, is a disputable one. It is examined how much an external structure plays a role in ordinary chemical reactions. The "information" of physics is not a semantic information. For such information we can refer to history of literature, telegraphic offices, genetics or biochemistry.     

Design of mineral medium for growth of <Emphasis Type="Italic">Actinomadura</Emphasis> sp. ATCC 39727, producer of the glycopeptide A40926: effects of calcium ions and nitrogen sources

Actinomadura sp. ATCC 39727 produces the glycopeptide antibiotic A40926, structurally similar to teicoplanin, with significant activity against Neisseria gonorrhoeae and precursor of the semi-synthetic antibiotic dalbavancin. In this study the production of A40926 by Actinomadura under a variety of growth conditions was investigated. The use of chemically defined mineral media allowed us to analyze the influence of carbon and nitrogen sources, phosphate, ammonium and calcium on the growth and the antibiotic productivity of Actinomadura. We confirm recent data [Gunnarsson et al. (2003) J Ind Microbiol Biotechnol 30:150–156] that low initial concentrations of phosphate and ammonium are beneficial for growth and A40926 production, and we provide new evidence that the production of A40926 is depressed by calcium, but promoted when l-glutamine or l-asparagine are used as nitrogen sources instead of ammonium salts.     

Endothelin 1 and 3 enhance neuronal nitric oxide synthase activity through ETB receptors involving multiple signaling pathways in the rat anterior hypothalamus

We have previously reported that endothelin 1 and 3 (ET-1, ET-3) through the ETB receptor decrease norepinephrine release in the anterior hypothalamus and activate the nitric oxide (NO) pathway. In the present work we sought to establish the receptors and intracellular mechanisms underlying the increase in nitric oxide synthase (NOS) activity stimulated by ET-1 and ET-3 in the rat anterior hypothalamus. Results showed that ETs-stimulated NOS activity was inhibited by a selective ETB antagonist (BQ-788), but not by a selective ETA antagonist (BQ-610). In addition, NOS activity was not altered in the presence of an ETA agonist (sarafotoxin 6b), but it was enhanced in the presence of a ETB agonist (IRL-1620). Both Nomega-nitro-L-arginine methyl ester (NOS inhibitor), and 7-nitroindazole (neuronal NOS inhibitor) diminished ETs-stimulated NOS activity. The stimulatory effect of ETs on NOS activity was inhibited in the presence of PLC, PKC, PKA and CaMK-II inhibitors (U-73122, GF-109203X, H-89 and KN-62, respectively), and the IP3 receptor selective antagonist, 2-APB. Our results showed that both ET-1 and ET-3 modulate neuronal NOS activity through the ETB receptor in the rat anterior hypothalamus involving the participation of the PLC-PKC/IP3 pathway as well as PKA and CaMK-II.     

Mutations of the CK2 phosphorylation site of Sic1 affect cell size and S-Cdk kinase activity in Saccharomyces cerevisiae

By sequence analysis we found an amino acid stretch centred on Serine201 matching a stringent CK2 consensus site within the C-terminal, inhibitory domain of Sic1. Here we show by direct mass spectrometry analysis that Sic1, but not a mutant protein whose CK2 phospho-acceptor site has been mutated to alanine, Sic1S201A, is actually phosphorylated in vitro by CK2 on Serine 201. Mutation of Serine 201 alters the coordination between growth and cell cycle progression. A significant increase of average protein content and of the average protein content at the onset of DNA synthesis is observed for exponentially growing cells harbouring the Sic1S201A protein. A strong reduction of the same parameters is observed in cells harbouring Sic1S201E. The deregulated coordination between cell size and cell cycle is also apparent at the level of S-Cdk activity.