Arachidonic acid-induced release of calcium in permeabilized human neutrophils

The addition of arachidonic acid to a suspension of digitonin-permeabilized human neutrophils was found to induce, in a dose-dependent manner (ED50 about 15 microM), the release of calcium from internal stores. Arachidic acid was without effect, while linoleic acid and linolenic acid were (on a concentration basis) at least 5-times less active than arachidonic acid. The activity of arachidonic acid appears to be due to the fatty acid itself and not to one of its metabolites. The pool of calcium mobilized by arachidonic acid includes that sensitive to inositol 1,4,5-triphosphate. These results demonstrate a significant intracellular role for arachidonic acid at the level of the internal mobilization of calcium in human neutrophils.     

Ciguatoxin and brevetoxins share a common receptor site on the neuronal voltage-dependent Na+ channel

Binding studies indicate that ciguatoxin and brevetoxin allosterically enhance in a very similar way the binding of [3H]batrachotoxinin A 20-alpha-benzoate to the neuronal Na+ channel protein. Moreover ciguatoxin competitively inhibits the binding of [3H]brevetoxin-3 to rat brain membranes. The affinity of ciguatoxin for the Na+ channel is at least 20-50-times higher than that of brevetoxin. These results indicate that ciguatoxin and brevetoxins act at the same binding site on the sodium channel.     

Molecular cloning of three homoeologous cDNAs encoding orthologs of the maize KNOTTED1 homeobox protein from young spikes of hexaploid wheat

The plant knotted1 (kn1)-like homeobox genes are known to play important roles in the maintenance of shoot apical meristem (SAM), determination of cell fate and differentiation of vegetative tissues. To study structural diversity of the three homologous loci encoding a KN1-like homeobox protein in the hexaploid wheat genome, we isolated clones from a cDNA library of young spikes of Japanese common wheat cultivar 'Norin 26'. Three different but highly homologous cDNAs were isolated and their sequences were determined. The mean homology of the deduced amino acid sequences was 96% as compared to the barley ortholog KNOX3. The wheat kn1-like homeobox proteins named WKNOX1 are encoded by a single set of homologous genes on the homologous group 4 chromosomes in the three component genomes of common wheat, i.e. 4A, 4B and 4D. The nucleotide sequence data and the Southern blot pattern suggested that the three homologous loci of wknox1 genes are highly conserved through polyploid evolution of wheat. They were expressed in SAM-containing shoots and young spikes but not in developed leaves, glumes and lemmas and callus tissues. The ectopic expression of the wknox1 was observed in lemma of wheat Hooded (Hd) mutants. The result suggested that the Hd gene is a dominant allele of the wknox1 locus on chromosome 4A.     

Tumor cells enhance their own CD44 cleavage and motility by generating hyaluronan fragments

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that interacts with cell-surface receptors, including CD44. Although HA usually exists as a high molecular mass polymer, HA of a much lower molecular mass that shows a variety of biological activities can be detected under certain pathological conditions, particularly in tumors. We previously reported that low molecular weight HAs (LMW-HAs) of a certain size range induce the proteolytic cleavage of CD44 from the surface of tumor cells and promote tumor cell migration in a CD44-dependent manner. Here, we show that MIA PaCa-2, a human pancreatic carcinoma cell line, secreted hyaluronidases abundantly and generated readily detectable levels of LMW-HAs ranging from approximately 10- to 40-mers. This occurred in the absence of any exogenous stimulation. The tumor-derived HA oligosaccharides were able to enhance CD44 cleavage and tumor cell motility. Inhibition of the CD44-HA interaction resulted in the complete abrogation of these cellular events. These results are consistent with the concept that tumor cells generate HA oligosaccha-rides that bind to tumor cell CD44 through the expression of their own constitutive hyaluronidases. This enhances their own CD44 cleavage and cell motility, which would subsequently promote tumor progression. Such an autocrine/paracrine-like process may represent a novel activation mechanism that would facilitate and promote the malignant potential of tumor cells.     

Multi-Stability and Multi-Instability Phenomena in a Mathematical Model of Tumor-Immune-Virus Interactions

Recent advances in virology, gene therapy, and molecular and cell biology have provided insight into the mechanisms through which viruses can boost the anti-tumor immune response, or can infect and directly kill tumor cells. A recent experimental report (Bridle et al. in Molec. Ther. 18(8):1430–1439, 2010) showed that a sequential treatment approach that involves two viruses that carry the same tumor antigen leads to an improved anti-tumor response compared to the effect of each virus alone. In this article, we derive a mathematical model to investigate the anti-tumor effect of two viruses, and their interactions with the immune cells. We discuss the conditions necessary for permanent tumor elimination and, in this context, we stress the importance of investigating the long-term effect of non-linear interactions. In particular, we discuss multi-stability and multi-instability, two complex phenomena that can cause abrupt transitions between different states in biological and physical systems. In the context of cancer immunotherapies, the transitions between a tumor-free and a tumor-present state have so far been associated with the multi-stability phenomenon. Here, we show that multi-instability can also cause the system to switch from one state to the other. In addition, we show that the multi-stability is driven by the immune response, while the multi-instability is driven by the presence of the virus.     

Chondroitin sulfates and their binding molecules in the central nervous system

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in the central nervous system (CNS) matrix. Its sulfation and epimerization patterns give rise to different forms of CS, which enables it to interact specifically and with a significant affinity with various signalling molecules in the matrix including growth factors, receptors and guidance molecules. These interactions control numerous biological and pathological processes, during development and in adulthood. In this review, we describe the specific interactions of different families of proteins involved in various physiological and cognitive mechanisms with CSs in CNS matrix. A better understanding of these interactions could promote a development of inhibitors to treat neurodegenerative diseases.     

Reproductive significance of feeding on saprobic and arbuscular mycorrhizal fungi by the collembolan, Folsomia candida

1. Collembolans have often been credited with negatively affecting arbuscular mycorrhizal (AM) symbioses, mainly by grazing and severing the associated external fungal network from host roots. However, most previous experiments were performed using relatively 'clean' systems where other, non-mycorrhizal, fungi were largely excluded. Yet, plant rhizospheres harbour a wide variety of highly palatable non-AM fungi, most of which have saprobic lifestyles.
2. In this study we isolated and cultured several rhizosphere fungi, and the collembolan , Folsomia candida , from the Long-Term Mycorrhiza Research Site, University of Guelph, Canada, to test the hypothesis that, given a choice, collembolans would prefer to feed on saprobic fungi and that such a choice is of adaptive significance to the animals.
3. A laboratory food preference experiment revealed that F. candida favours common saprobic fungi over a variety of AM fungi. Coincidentally, fecundity levels across two Folsomia generations were higher when animals fed exclusively on the preferred fungus, Alternaria alternata . When fed less palatable fungi, fecundity was greatly reduced; in fact animals from the F1 generation were unable to produce any eggs when placed on an exclusive diet of one of the following three AM fungi, Acaulospora spinosa, Scutellospora calospora and Gigaspora gigantea .
4. These results indicate that a strict diet of AM fungi by collembolans has reproductive consequences. Therefore, we propose that under natural conditions these animals spend more time feeding on common saprobic fungi rather than their AM counterparts. This suggests that previous 'clean' studies that investigated the interactions between collembolans and AM fungi may have reported exaggerated effects of animal grazing. The influence of collembolans on the functioning of AM symbioses, under more natural conditions, remains not well understood.     

Further improvements to the photoelectric method for measuring motile responses of chromatophores

With the intention of simplifying construction and operation, improvements have now been made to a photoelectric system for measuring the motile responses of chromatophores. Introduction of chop-per-stabilized operational amplifiers with a complimentary metal-oxide semiconductor (C-MOS) input has brought about a much improved stability of the electronics. Such a feature has been found to be especially suitable for measurements requiring higher amplification and longer periods of time, e.g., the detection of the effects of various factors on bright-colored chromatophores. The use of appropriate color filters that limit the spectral range of light used for measurement has also proven to be important. By installing a small filter close to the photosensor, we can now record the responses of particular types of chromatophores more selectively, while visually monitoring the states of all kinds of chromatophores in natural color. To minimize the influence of motile activities of xanthophores and/or erythrophores, the use of an orange-to-red long-pass filter is appropriate to optimize recording the melanophore responses. By contrast, the responses of xanthophores or erythrophores can be recorded more easily by employing a violet-to-blue band-pass filter, because that increases the contrast of images of these cells against the background. Using an orange-red variety of the medaka Oryzias, we have also recorded photometrically the responses of leucophores, whose organelles are light-scattering. A long-pass filter was efficient in excluding the influences of co-existing xanthophores.     

Ultrastructure of the Circulatory System of the Phoronid Phoronopsis harmeri Pixell, 1912. 2. Main vessels

The ultrastructure of the wall of the main blood vessels of the phoronid Phoronopsis harmeri is described. The walls of the lophophoral and left lateral vessels consist of myoepithelial cells of the coelomic lining (peritoneal cells), a thin basal lamina, and an incomplete endothelial lining. In the head region of the body, the wall of the medial vessel consists of myoepithelial cells of the coelomic lining (peritoneal cells), a basal lamina, and true muscular endothelial cells. The anterior part of the medial vessel functions as the heart. In the anterior part of the body, the medial vessel wall consists of five layers: the external nonmuscular coelothelium, a layer of the extracellular matrix, the internal muscular coelothelium, an internal layer of the extracellular matrix, and an incomplete endothelial lining. The complicated structure of the medial vessel wall may be explained by the superimposition of the lateral mesentery on the ordinary vessel wall.     

Photosynthetic responses of Eucalyptus nitens (Deane and Maiden) Maiden to green pruning

 Three-year-old Eucalyptus nitens (Deane and Maiden) Maiden trees and 1-year-old ramets of a single clone of E. nitens were pruned to remove 0, 50% or 70% of the green crown length. This was equivalent to removal of 0, 55% or 88% of foliage area of trees, and 0, 77% or 94% of foliage area of ramets. CO₂ assimilation (A) and stomatal conductance (g_s) were measured at constant illumination in five height zones and three foliage-age classes of trees over a 16-month period following pruning. Foliar nitrogen (N) and phosphorus (P) concentrations were determined for each measurement time during the first 12 months of the experiment. In ramets A and g_s were measured in four height zones and two foliage-age classes over a six-week period, and N and P concentrations were measured only once, at the end of the experiment. Rates of A increased by up to 175% following pruning. This response occurred throughout the canopy irrespective of position in the crown or foliage age. The magnitude of the response was generally greater in ramets than in trees, and increased with increasing severity of pruning. The initiation of the response was later, and the duration of the response was longer, in trees than ramets. In the lower crown of trees there was evidence of delayed senescence following pruning. Photosynthetic enhancement was not related to changes in foliar N concentrations. The ratio of A/N increased in many zones following pruning, especially after more severe defoliation. There was no evidence that changes in P concentrations were responsible for the result. The increases in A may have been related to changes in g_s, as maximum values of g_s were greater, and the ratio of A/g_s was generally lower, in pruned than unpruned plants. Received: 31 December 1996 / Accepted: 19 August 1997