Wnt signaling involvement in beta-amyloid-dependent neurodegeneration

Alzheimer's disease (AD) is a progressive dementia paralleled by selective neuronal death, which is probably caused by the cytotoxic effects of the amyloid-beta peptide (Abeta). We have observed that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and that activation of this signaling cascade prevent such cytotoxic effects. Therefore we propose that compounds which mimic this signaling cascade may be candidates for therapeutic intervention in Alzheimer's patients.     

Membrane topology of the acyl-lipid desaturase from Bacillus subtilis

The Bacillus subtilis acyl-lipid desaturase (Delta5-Des) is an iron-dependent integral membrane protein, able to selectively introduce double bonds into long chain fatty acids. Structural information on membrane-bound desaturases is still limited, and the present topological information is restricted to hydropathy plots or sequence comparison with the evolutionary related alkane hydroxylase. The topology of Delta5-Des was determined experimentally in Escherichia coli using a set of nine different fusions of N-terminal fragments of Delta5-Des with the reporter alkaline phosphatase (Delta5-Des-PhoA). The alkaline phosphatase activities of cells expressing the Delta5-Des-PhoA fusions, combined with site-directed mutagenesis of His residues identified in most desaturases, suggest that a tripartite motif of His essential for catalysis is located on the cytoplasmic phase of the membrane. These data, together with surface Lys biotinylation experiments, support a model for Delta5-Des as a polytopic membrane protein with six transmembrane- and one membrane-associated domain, which likely represents a substrate-binding motif. This study provides the first experimental evidence for the topology of a plasma membrane fatty acid desaturase. On the basis of our results and the presently available hydrophobicity profile of many acyl-lipid desaturases, we propose that these enzymes contain a new transmembrane domain that might play a critical role in the desaturation of fatty acids esterified in glycerolipids.     

Partial cloning and expression of the cyclin B gene in the ovary of the bullseye puffer (Sphoeroides annulatus)

The bullseye puffer is a marine fish species with great potential for aquaculture in Mexico, and the understanding of its reproductive physiology at every level of biological organization is essential in order to succeed. Several molecules orchestrate the complex process of oocyte maturation and spawning. One of these molecules is cyclin B, which is the regulatory subunit of the maturation-promoting factor. In this study, a fragment of the cyclin B gene was isolated from the ovary of the bullseye puffer using an RT-PCR approach. The gene fragment was homologous to the cyclin B2 gene of other vertebrate species. Similar levels of cyclin B gene expression were detected in ovaries at different developmental stages, except for atretic ovaries from captive fish which did not spawn. However, cyclin B gene expression was maintained in captive fish treated with LHRH-a to induce spawning, and appeared to be similar to the pattern observed in wild fish. It is possible that the reduced expression of cyclin B in atretic ovaries is the result of mRNA degradation during atresia. Alternatively, reduced gene expression could be a controlling factor in the process of oocyte reabsorption since cyclin B is required for final oocyte maturation and ovulation.     

Lack of arginine decarboxylase in Trypanosoma cruzi epimastigotes

The presence of arginine decarboxylase (ADC) enzymatic activity in Trypanosoma cruzi epimastigotes is still a matter of controversy due to conflicting results published during the last few years. We have investigated whether arginine might indeed be a precursor of putrescine via agmatine in these parasites. We have shown that wild-type T. cruzi epimastigotes cultivated in a medium almost free of polyamines stopped their growth after several repeated passages of cultures in the same medium, and that neither arginine nor omithine were able to support or reinitiate parasite multiplication. In contrast, normal growth was quickly resumed after adding exogenous putrescine or spermidine. The in vivo labelling of parasites with radioactive arginine showed no conversion of this amino acid into agmatine, and attempts to detect ADC activity measured by the release of CO2 under different conditions in T. cruzi extracts gave negligible values for all strains assayed. The described data clearly indicate that wild-type T. cruzi epimastigotes lack ADC enzymatic activity.     

Primates as pets in Mexico City: an assessment of the species involved, source of origin, and general aspects of treatment

The large human populations in cities are an important source of demand for wildlife pets, including primates, and not much is known about the primate species involved in terms of their general origin, the length of time they are kept as pets, and some of the maintenance problems encountered with their use as pets. We report the results of a survey conducted in Mexico City among primate pet owners, which was aimed at providing some of the above information. We used an ethnographic approach, and pet owners were treated as informants to gain their trust so that we could enter their homes and learn about the life of their primate pets. We surveyed 179 owners of primate pets, which included 12 primate species. Of these, three were native species (Ateles geoffroyi, Alouatta pigra, and A. palliata). The rest were other neotropical primate species not native to Mexico, and some paleotropical species. Spider monkeys and two species of howler monkeys native to Mexico accounted for 67% and 15%, respectively, of the primate cases investigated. The most expensive primate pets were those imported from abroad, while the least expensive were the Mexican species. About 45% of the native primate pets were obtained by their owners in a large market in Mexico City, and the rest were obtained in southern Mexico. Although they can provide companionship for children and adults, primate pets are subject to a number of hazards, some of which put their lives at risk. The demand by city dwellers for primate pets, along with habitat destruction and fragmentation, exerts a significant pressure on wild populations in southern Mexico.     

D4 Dopamine and Metabotropic Glutamate Receptors in Cerebral Cortex and Striatum in Rat Brain

The characterization of the functional interactions between the metabotropic glutamate receptors (mGluR) and the dopaminergic (DR) receptors in the corticostriatal projections may provide a possible interpretation of synaptic events in the basal ganglia. It has been suggested that presynaptic D2-type receptor located on glutamatergic corticostriatal neurons regulates the release of glutamate. In a first approach we have studied the cellular distribution of the D4R and the mGluRs in cerebral cortex and striatum employing immunocytochemistry. D4R positive neurons were particularly numerous in medial prefrontal cortex mainly occupying layers II and III. An even distribution was found on small round-shaped neurons in the striatum. Group I mGluR1-like immunoreactivity (mGluR1-LI) was found in medial and deep layers of the cerebral cortex while group III mGluR4a labeled more superficial layers; group II mGluR2/3 signal was intense on fine fibers with a punctate appearance. In the striatum, mGluR1 and mGluR2/3 stained mainly fibers while mGluR4a labeled round shaped cell bodies. After lateral ventricular injection of colchicine, an axonal transport and firing activity blocker, D4R labeling significantly increased in cerebral cortex and decreased in the striatum. mGluR1 and mGluR4a signal decreased in cerebral cortex and only mGluR4a signal decreased in the striatum. These results support previous reports indicating a presynaptic localization of D4R in the striatum. In contrast, striatal mGluR1 appears to be a postsynaptic receptor probably synthesized in situ. Our results do not support the hypothesis of a colocalization of D4 receptor and one or more of the metabotropic glutamatergic receptors studied here.     

Flunitrazepam partitioning into natural membranes increases surface curvature and alters cellular morphology

In recent studies, we showed that flunitrazepam (FNTZ) and other benzodiazepines interact with artificial phospholipid membranes locating at the polar head group region, inducing a membrane expansion, reducing the molecular packing and reorganising molecular dipoles. In the present paper we investigated the possibility that those phenomena could be transduced into changes in the curvature of membranes from natural origin. Hence we studied the effect of FNTZ on cellular morphology using human erythrocyte as a natural assay system. Shape changes of erythrocytes were evaluated by light microscopy and expressed as a morphological index (MI). FNTZ induced echinocytosis in a time-dependent manner with MI values significantly higher than those of control (without drug) or DMSO (vehicle) samples. Lidocaine, a local anesthetic known to induce stomatocytosis by incorporating in the inner monolayer, counterbalanced the concentration-dependent FNTZ crenating effects. FNTZ induced protective effects, compared with control and DMSO, against time-dependent hemolysis. Hypotonic-induced hemolysis, was also lowered by FNTZ in a concentration-dependent manner. Both antihemolytic effects suggested a drug-induced membrane expansion allowing a greater increase in cell volume before lysis. In such a complex system like a cell, curvature changes triggered by drug partitioning towards the plasma membrane, might be an indirect effect exerted through modifications of ionic-gradients or by affecting cytoskeleton-membrane linkage. In spite of that, the curvature changes can be interpreted as a mechanism suitable to relieve the tension generated initially by drug incorporation into the bilayer and may be the resultant of the dynamic interactions of many molecular fluxes leading to satisfy the spontaneous membrane curvature.     

Three maize root-specific genes are not correctly expressed in regenerated caps in the absence of the quiescent center

The quiescent center is viewed as an architectural template in the root apical meristem of all angiosperm and gymnosperm root tips. In roots of Arabidopsis thaliana (L.) Heynh., the quiescent center inhibits differentiation of contacting initial cells and maintains the surrounding initial cells as stem cells. Here, the role of the quiescent center in the development of the maize (Zea mays L.) root cap has been further explored. Three maize root-specific genes were identified. Two of these were exclusively expressed in the root cap and one of them encoded a GDP-mannose-4,6-dehydratase. Most likely these two genes are structural, tissue-specific markers of the cap. The third gene, a putative glycine-rich cell wall protein, was expressed in the cap and in the root epidermis and, conceivably is a positional marker of the cap. Microsurgical and molecular data indicate that the quiescent center and cap initials may regulate the positional and structural expression of these genes in the cap and thereby control root cap development. Received: 22 September 1999 / Accepted: 9 November 1999     

Woody vegetation structure of xeric forest stands under different edaphic site conditions and disturbance histories in the Biosphere Reserve 'Parque Costero del Sur', Argentina

We studied stand structures and soil properties in an old-growth forest and two 30-yr-old second-growth stands. In the old-growth forest, the total density and basal area average 1566 trees > 1.25 m height ha^-1 and 46.73 m² ha^-1. The dominant trees are Scutia buxifolia and Celtis tala. Using multivariate techniques we distinguished three stands: PS1, dominated by S. buxifolia, is 1000 m far from the river. Its soil is shallow and loamy. PS2 and PS3, co-dominated by S. buxifolia and C. tala, are over 1200 m distant from the river. There the soil is deeper and has thicker texture and higher phosphorus and calcium concentrations than the near-the-river forest soil. Scutia buxifolia shows reverse J-shaped size-distributions and has morphological features of stress-tolerant species. Celtis tala shows oscillating decay size-curves that suggest recruitment pulses related to small gaps and it has morphological features of competitive species. Celtis tala was selectively cut in the past in the second-growth stands SNRD and SRD. The stand SNRD, 1000 m far from the river, is dominated by S. buxifolia. The second species is Schinus polygamus which presents the bell-shaped size-structure of the pioneer species. SNRD does not differ from its old-growth counterpart PS1 in total tree density, basal area and tree branching. The stand SRD, over 1200 m distant from the river, is co-dominated by S. buxifolia and by C. tala trees regenerated from stumps. SRD does not differ from its old-growth counterparts PS2 and PS3 in total tree density and basal area. As to tree branching, it does not differ from PS3, but differs from PS2. All the stands are being invaded by the exotic tree Ligustrum lucidum.The differences between the old-growth stands seem to be related to the gradients of soil texture and nutrient concentrations raising edaphic stress towards the river. In SNRD, the stress, the stress-tolerance of S. buxifolia, and the aptitude of S. polygamus to recruit in disturbed habitats seem to have prevented the post-logging recruitment of C. tala. In SRD, C. tala regenerated possibly due to a better competitive performance in a more favorable site. Under protection the second-growth stands recovered the old-growth quantitative features. We recommend the restoration of the qualitative features and the control of L. lucidum.     

Amyloidogenic Propensity of a Natural Variant of Human Apolipoprotein A-I: Stability and Interaction with Ligands

A number of naturally occurring mutations of human apolipoprotein A-I (apoA-I) have been associated with hereditary amyloidoses. The molecular mechanisms involved in amyloid-associated pathology remain largely unknown. Here we examined the effects of the Arg173Pro point mutation in apoA-I on the structure, stability, and aggregation propensity, as well as on the ability to bind to putative ligands. Our results indicate that the mutation induces a drastic loss of stability, and a lower efficiency to bind to phospholipid vesicles at physiological pH, which could determine the observed higher tendency to aggregate as pro-amyloidogenic complexes. Incubation under acidic conditions does not seem to induce significant desestabilization or aggregation tendency, neither does it contribute to the binding of the mutant to sodium dodecyl sulfate. While the binding to this detergent is higher for the mutant as compared to wt apoA-I, the interaction of the Arg173Pro variant with heparin depends on pH, being lower at pH 5.0 and higher than wt under physiological pH conditions. We suggest that binding to ligands as heparin or other glycosaminoglycans could be key events tuning the fine details of the interaction of apoA-I variants with the micro-environment, and probably eliciting the toxicity of these variants in hereditary amyloidoses.