Chromosome 17 abnormalities and lack of TP53 mutations in paediatric central nervous system tumours

Central nervous system (CNS) tumours are the most common solid tumours in children. Cytogenetic and molecular genetic studies of these neoplasms have previously shown abnormalities of chromosome 17, implicating genes on this autosome in tumorigenesis. To identify mutations in the TP53 tumour suppressor gene (17p13.1), we have sequenced the five highly conserved regions of this gene in 29 mixed paediatric CNS tumors. No mutations were detected by this analysis. In order to identify other candidate disease loci on chromosome 17, we have carried out a detailed deletion mapping analysis using 16 polymorphic DNA markers on 19 of the above tumours and an additional four cases. Abnormalities of chromosome 17 occurred in nine cases (39%), six of which were primitive neuroectodermal tumour (PNET)-medulloblastomas. These findings suggest that it is unlikely that the TP53 gene is directly involved in the development of common paediatric brain tumours. This is in contrast to findings from adult brain and other tumour types. Moreover, the frequency of chromosome 17 aberrations, especially in PNET-medulloblastomas, suggests that other genes on this chromosome contribute to tumourigenesis.     

Purification and characterization of the catabolic α-acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris

The -acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris was purified to homogeneity in SDS-PAGE. The enzyme is a trimer of 3×55,000 Da. It was unstable but could be preserved by addition of pyruvate and thiamine pyrophosphate in the buffer. The enzyme exhibits Michaelis-Menten kinetics, and K _m for pyruvate is 10 mM. Three intermediates in glucose metabolism (ATP, 3-phosphoglycerate, and phosphoenolpyruvate) exhibit a noncompetitive inhibition towards the enzyme. This enzyme does not require any divalent metal ion for activity. The -acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris is not inhibited by the branched-chain amino acids (valine, leucine, and isoleucine), is FAD independent, and displays an optimal activity at pH 5.3. Therefore, it can be concluded that the purified enzyme belongs to the catabolic -acetolactate synthases, involved in the 2,3-butanediol pathway but not in branchedchain amino acids biosynthesis.     

Reproductive ecology of five pipefish species in one eelgrass meadow

Synopsis Synopsis Pipefishes have rarely been watched in the wild and have never before been followed in their common seagrass habitats. This study explores the reproductive ecology of five species of pipefishes living in a Swedish eelgrass meadow during parts of four breeding seasons, tagging four of the species. Pipefish are remarkable for their specialised paternal care: only males aerate, osmoregulate and nourish the developing embryos. Two of the species (Entelurus aequoreus andNerophis ophidion) have simple ventral gluing of eggs on the trunk while three species (Syngnathus acus, S. rostellatus andS. typhle) have fully enclosed brood pouches on their tails. Males of the former species receive eggs from one female while males of the genusSyngnathus receive partial clutches from several females. Sex ratios of adults on the site differed from equal to male-biased to female-biased, according to species.S. typhle were most numerous and were resighted most often. They were present throughout the breeding season whereas there were temporal shifts in the presence of the other species on the meadow and in some sex ratios. Most species occurred in the deeper, denser part of the meadow but there was some habitat separation by species and sex. All species tended to stay low in the eelgrass, primarily coming up above the eelgrass to display and mate. No species showed site fidelity either to a home range or to the meadow, withE. aequoreus adults spending least time on the meadow. Sexual size dimorphism differed: males were larger inS. rostellatus, the same size inS acus and smaller in the other species. Although the species overlap in habitat requirements and breeding season, the only observed interspecific interactions were abortive courtships betweenSyngnathus species.     

Cell lineage patterns and homeotic gene activity during Antirrhinum flower development

Background: Homeotic genes controlling the identity of flower organs have been characterized in several plant species. To determine whether cells expressing these genes are specified to follow particular developmental fates, we have studied the pattern of cell lineages in developing flowers of Antirrhinum. Each flower has four whorls of organs, and progenitor cells of these can be marked at particular stages of development using a temperature-sensitive transposon. This allows the cell lineages in the flower to be followed, as well as giving information about rates of cell division.Results We show here that, prior to the emergence of organ primordia, cells in the floral meristem have not been allocated organ identities. After this time, lineage restrictions arise between whorls, correlating with the onset of expression of genes that control organ identity. A further lineage restriction appears slightly later on, between the dorsal and ventral surfaces of the petal. Our results further suggest that the rates of cell division fluctuate during key stages of meristem development, perhaps as a consequence of meristem-identity gene expression.Conclusion The patterns of lineage restriction and organ-identity gene expression in early floral meristems are consistent with some cells being allocated specific identities at about this stage of development. Plant cells cannot move relative to each other, so lineage restrictions in plants may reflect particular orientations and/or rates of growth at boundary regions.     

Stability in an evolutionary game

A behavior or strategy which is evolutionarily stable must be both optimal and stable. The strategy must be optimal in that it maximizes the expected fitness of all the individuals using it. In addition, the strategy must be resistant to invasion by a mutant. The difference between the Nash solution of game theory and the ESS used in ecology is that the Nash solution only satisfies an optimality criterion and not an evolutionary stability criterion. We extend the ESS definition of Maynard Smith and Price so that it can be applied directly to two-strategy evolutionary games. The concept of a balanced game is introduced, and necessary conditions are derived which are similar to the Nash necessary conditions. The balanced game necessary conditions may be used for direct calculation of ESS candidates. These results are used to examine the optimal flowering time of an annual plant experiencing competition from neighboring plants. The plant competition model is general, and the results may be applied to a wide range of interference competition problems.     

Characterization of neurotensin binding to rat gastric smooth muscle receptor sites

The binding of monoiodo 125I-Trp11-neurotensin to purified rat gastric fundus smooth muscle plasma membranes was characterized. Specific binding of ligand in subcellular fractions from rat fundus smooth muscle showed a distribution that paralleled that of several plasma membrane marker enzymes. 125I-Trp11-neurotensin binding to smooth muscle plasma membranes at 25 degrees C was maximal at 30 min, reversible and saturable. Scatchard analysis of equilibrium data indicated the existence of two classes of binding sites with dissociation constants (Kd) of 56 pmol and 1.92 nM, and corresponding binding capacities (Bmax) of 6.6 fmol/mg and 11.4 fmol/mg of membrane protein. Analogues and fragments of neurotensin competed for 125I-Trp11-neurotensin binding with a rank order of potency similar to that previously reported for their contracting effect in rat fundus strips. Na+ decreased in a concentration dependent manner the binding of labelled ligand to the high affinity site. At 100 mM, Na+ induced a 6-fold increase in the IC50 of neurotensin for inhibition of 125I-Trp11-neurotensin binding. At this concentration of Na+, the IC50 for neurotensin was 1 nM, a value close to the Kd of the low affinity site.     

A role for ornithine in the regulation of putrescine accumulation and ornithine decarboxylase activity in Reuber H35 hepatoma cells

We investigated the ability of intracellular ornithine to alter both the biosynthesis of putrescine and the activity of ornithine decarboxylase in Reuber H35 hepatoma cells in culture incubated with 12-O-tetradecanoylphorbol 13-acetate (TPA). In confluent cultures of H35 cells, the addition of TPA (1.6 μM) caused the activity of ornithine decarboxylase to increase by more than 100-fold within 4 h. When exogenous ornithine (0.1–1.0 mM) was added to the culture medium with TPA, a marked dose-dependent increase in the production of putrescine was observed. The activity of ornithine decarboxylase in the same cultures incubated with ornithine decreased in a similar dose-dependent manner. The addition of arginine (0.1–1.0 mM) (but not lysine or histidine) to the H35 cells in culture concomitant with TPA also led to a relative increase in putrescine biosynthesis and a decrease in ornithine decarboxylase activity compared to cultures not receiving the amino acids. A similar response to exogenous ornithine and TPA was observed in a series of less confluent rapidly growing cultures which were in culture for a shorter period of time. The confluent cultures possessed a basal level of arginase (55 units/mg protein) which increased approx. 2-fold upon treatment with TPA. The intracellular concentration of ornithine in the unstimulated cells was in the order of 0.02–0.03 mM. Upon incubation of the cells with exogenous ornithine or arginine, the intracellular pools of these amino acids increased 4- to 8-fold.     

Effect of puromycin on cartilage proteoglycan structure and capacity to bind hyaluronic acid

Rat chondrosarcoma chondrocytes were cultured in the presence of puromycin to induce premature termination of core protein precursor. The structure and function of intracellular and extracellular proteoglycans were assessed by molecular sieve chromatography and polyacrylamide gel electrophoresis. [³H]Serine incorporation was maximally inhibited by 3 × 10^?4m puromycin but unaffected by 10 ^?5m puromycin. Proteoglycans synthesized in the presence of puromycin exhibited increased monomer size due to increased chondroitin sulfate chain size, typical of proteoglycans synthesized in the presence of protein synthesis inhibitors, but no loss in ability to bind to hyaluronic acid; and no loss in core protein size was observed after treatment with chondroitinase. These data suggest that chondrocytes select only completed or nearly completed core protein molecules to process into proteoglycans.     

Initial evaluation of the non-sulfhydryl-containing converting enzyme inhibitor MK-521 in hypertensive humans

MK-521 is a new orally active, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor. Single doses of 2.5, 5.0, 10.0, and 20.0 mg were administered to nine hypertensive patients alternating with placebo. All doses of MK-521 caused profound suppression of ACE activity for more than 24 h and decreased standing diastolic blood pressure for more than 12 h without changes in pulse rate. Although there was no further reduction in blood pressure with doses above 5.0 mg, the duration of action was prolonged for more than 24 h with the higher doses. Serum MK-521 concentrations increased with dosage, and ACE was inhibited maximally at concentrations above 10 ng/ml. In this initial study, MK-521 was well tolerated and proved to be a potent and long-acting antihypertensive agent.     

β-1-4-and β-1-3-glucan synthases are associated with the plasma membrane of the fungus Saprolegnia

Cytoplasmic membranes from mycelium or protoplasts of Saprolegnia monoica (a cellulosic cell-wall fungus) were separated by continuous sucrose-density-gradient centrifugation. Glucan synthases assayed at low (micromolar uridine 5-diphosphate (UDP) glucose for -1-4-glucan synthase) and high (millimolar UDP glucose for -1-3-glucan synthase) substrate concentrations were associated with membranes exhibiting vanadate-sensitive, oligomycin-insensitive ATPase and equilibrating at density 1.16 g cm^-3. Synthase activities were also bound to membranes of lower density (1.10 and 1.145 g cm^-3). Plasma membranes were stabilized by coating protoplasts with concanavalin A. After lysis of the protoplasts, plasma membranes recovered by low centrifugal forces were isolated in continuous isopycinic gradients. Both synthase activities peaked with [³H]concanavalin A and Na-vanadate ATPase indicating that the synthetases are located at the plasma membrane. Treatments of intact protoplasts with cold glutaraldehyde or proteases before disruption lead to a diminution of glucan-synthase activities indicating that at least part of the enzymes of plasma membrane face the outside of the cell.Abbreviations ConA concanavalin A - ER endoplasmic reticulum - GSI -1,4-glucan synthase - GSH -1,3-glucan synthase - UDP uridine 5-diphosphate