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Biomedical subjects

S Teixeira

Publications and source records attributed to S Teixeira.

13 recordsLinked to original sources
PubMed2006

Genetic structure at range edge: low diversity and high inbreeding in Southeast Asian mangrove (Avicennia marina) populations.

Understanding the genetic composition and mating systems of edge populations provides important insights into the environmental and demographic factors shaping species' distribution ranges. We analysed samples of the mangrove Avicennia marina from Vietnam, northern Philippines and Australia, with microsatellite markers. We compared genetic diversity and structure in edge (Southeast Asia, and Southern Australia) and core (North and Eastern Australia) populations, and also compared our results with previously published data from core and southern edge populations. Comparisons highlighted significantly reduced gene diversity and higher genetic structure in both margins compared to core populations, which can be attributed to very low effective population size, pollinator scarcity and high environmental pressure at distribution margins. The estimated level of inbreeding was significantly higher in northeastern populations compared to core and southern populations. This suggests that despite the high genetic load usually associated with inbreeding, inbreeding or even selfing may be advantageous in margin habitats due to the possible advantages of reproductive assurance, or local adaptation. The very high level of genetic structure and inbreeding show that populations of A. marina are functioning as independent evolutionary units more than as components of a metapopulation system connected by gene flow. The combinations of those characteristics make these peripheral populations likely to develop local adaptations and therefore to be of particular interest for conservation strategies as well as for adaptation to possible future environmental changes.

Australia↗
PubMed2005

Assessing genetic diversity in clonal organisms: low diversity or low resolution? Combining power and cost efficiency in selecting markers.

The increasing use of molecular tools to study populations of clonal organisms leads us to question whether the low polymorphism found in many studies reflects limited genetic diversity in populations or the limitations of the markers used. Here we used microsatellite datasets for two sea grass species to provide a combinatory statistic, combined with a likelihood approach to estimate the probability of identical multilocus genotypes (MLGs) to be shared by distinct individuals, in order to ascertain the efficiency of the markers used and to optimize cost-efficiently the choice of markers to use for deriving unbiased estimates of genetic diversity. These results strongly indicate that conclusions from studies on clonal organisms derived using markers showing low polymorphism, including microsatellites, should be reassessed using appropriate polymorphic markers.

Alismatales↗
PubMed2005

Effects of chronic heart disease on skeletal muscle fiber size.

Size changes in muscle fibers of subjects with chronic heart disease (CHD) have been reported, although a consensus has not been achieved. The aims of the present study were to investigate a possible association between CHD and fiber size changes in the brachial biceps compared to subjects without heart disease. Forty-six muscle samples were obtained in autopsies of individuals (13 to 84 years) without neuromuscular disorders, 19 (10 males and 9 females) with, and 27 (14 males and 13 females) without CHD. In all cases muscle sections were stained with hematoxylin and eosin and processed for the visualization of myofibrillar ATPase activity. The lesser diameter of type 1 and type 2 fibers was obtained tracing their outlines (at least 150 fibers of each type per sample) onto an image analyzer connected to a computer. The results were analyzed statistically comparing males and females with and without CHD. Type 1 fiber mean lesser diameters were 51.51 and 54.52 microm in males (normal range 34-71 microm) and 45.65 and 55.42 microm in females (normal range 34-65 microm) without and with CHD, respectively; type 2 fibers measured 54.31, 58.23, 41.15, and 49.57 microm, respectively (normal range 36-79 microm for males and 32-59 microm for females). No significant difference in fiber size was detected in 24 males with and without CHD, while in 22 females there was a significant increase in size in those with cardiomyopathy. We concluded that CHD does not determine significant changes in fiber size. However, in females, there is some hypertrophy which, despite within normal range, may reflect morphologic heterogeneity of the sample, or the daily life activities in the upper limbs as a compensatory mechanism to fatigability that affect predominantly the lower limbs in subjects with CHD.

Adolescent↗
PubMed2001

Tungsten-containing formate dehydrogenase from Desulfovibrio gigas: metal identification and preliminary structural data by multi-wavelength crystallography.

The tungsten-containing formate dehydrogenase (W-FDH) isolated from Desulfovibrio gigas has been crystallized in space group P2(1), with cell parameters a = 73.8 A, b = 111.3 A, c = 156.6 A and beta = 93.7 degrees. These crystals diffract to beyond 2.0 A on a synchrotron radiation source. W-FDH is a heterodimer (92 kDa and 29 kDa subunits) and two W-FDH molecules are present in the asymmetric unit. Although a molecular replacement solution was found using the periplasmic nitrate reductase as a search model, additional phasing information was needed. A multiple-wavelength anomalous dispersion (MAD) dataset was collected at the W- and Fe-edges, at four different wavelengths. Anomalous and dispersive difference data allowed us to unambiguously identify the metal atoms bound to W-FDH as one W atom with a Se-cysteine ligand as well as one [4Fe-4S] cluster in the 92 kDa subunit, and three additional [4Fe-4S] centers in the smaller 29 kDa subunit. The D. gigas W-FDH was previously characterized based on metal analysis and spectroscopic data. One W atom was predicted to be bound to two molybdopterin guanine dinucleotide (MGD) pterin cofactors and two [4Fe-4S] centers were proposed to be present. The crystallographic data now reported reveal a selenium atom (as a Se-cysteine) coordinating to the W site, as well as two extra [4Fe-4S] clusters not anticipated before. The EPR data were re-evaluated in the light of these new results.

Crystallography, X-Ray↗
PubMed2001

Anisotropic refinement of the structure of Thermoascus aurantiacus xylanase I.

The isotropic crystallographic model of the structure of xylanase I from Thermoascus aurantiacus (TAXI) has now been refined anisotropically at 1.14 A resolution to a standard residual of R = 11.1% for all data. TAXI is amongst the five largest proteins deposited in the Protein Data Bank to have been refined with anisotropic displacement parameters (ADPs) at this level of resolution. The anisotropy analysis revealed a more isotropic distribution of anisotropy than usually observed previously. Adding ADPs resulted in high-quality electron-density maps which revealed discrepancies from the previously suggested primary sequences for this enzyme. Side-chain conformational disorder was modelled for 16 residues, including Trp275, a bulky residue at the active site. An unrestrained refinement was consistent with the protonation of the catalytic acid/base glutamate and the deprotonation of the nucleophile glutamate, as required for catalysis. The thermal stability of TAXI is reinterpreted in the light of the new refined model.

Amino Acid Sequence↗
PubMed2000

Crystallization and preliminary X-ray analysis of a membrane-bound nitrite reductase from Desulfovibrio desulfuricans ATCC 27774.

Nitrite reductase from the sulfate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 is a multihaem (type c) membrane-bound enzyme that catalyzes the dissimilatory conversion of nitrite to ammonia. Crystals of the oxidized form of this enzyme were obtained using PEG and CaCl(2) as precipitants in the presence of 3--(decylmethylammonium)propane-1-sulfonate and belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 78.94, b = 104.59, c = 143.18 A. A complete data set to 2.30 A resolution was collected using synchrotron radiation at the ESRF. However, the crystals may diffract to beyond 1.7 A and high-resolution data will be collected in the near future.

Bacterial Proteins↗
PubMed1999

Structural studies by X-ray diffraction on metal substituted desulforedoxin, a rubredoxin-type protein.

Desulforedoxin (Dx), isolated from the sulfate reducing bacterium Desulfovibrio gigas, is a small homodimeric (2 x 36 amino acids) protein. Each subunit contains a high-spin iron atom tetrahedrally bound to four cysteinyl sulfur atoms, a metal center similar to that found in rubredoxin (Rd) type proteins. The simplicity of the active center in Dx and the possibility of replacing the iron by other metals make this protein an attractive case for the crystallographic analysis of metal-substituted derivatives. This study extends the relevance of Dx to the bioinorganic chemistry field and is important to obtain model compounds that can mimic the four sulfur coordination of metals in biology. Metal replacement experiments were carried out by reconstituting the apoprotein with In3+, Ga3+, Cd2+, Hg2+, and Ni2+ salts. The In3+ and Ga3+ derivatives are isomorphous with the iron native protein; whereas Cd2+, Hg2+, and Ni2+ substituted Dx crystallized under different experimental conditions, yielding two additional crystal morphologies; their structures were determined by the molecular replacement method. A comparison of the three-dimensional structures for all metal derivatives shows that the overall secondary and tertiary structures are maintained, while some differences in metal coordination geometry occur, namely, bond lengths and angles of the metal with the sulfur ligands. These data are discussed in terms of the entatic state theory.

Amino Acid Sequence↗
PubMed1993

Interleukin-2-dependent transcriptional and post-transcriptional regulation of transferrin receptor mRNA.

Interleukin-2 (IL-2) controls the proliferation of the murine T cell line B6.1 and induces transferrin receptor (TfR) mRNA steady-state levels 50-fold when added to arrested, IL-2-deprived cells. In addition, TfR mRNA is post-transcriptionally regulated by intracellular iron. Low iron levels activate a cytoplasmic RNA-binding protein, called iron regulatory factor (IRF) or iron-responsive element-binding protein, which coordinately stabilizes TfR mRNA and inhibits ferritin mRNA translation. Since ferritin expression is known to be modulated by cytokines, we decided to investigate the mechanism by which IL-2 activates TfR gene expression in B6.1 cells. Induction by IL-2 of both nuclear and cytoplasmic TfR RNA was compared with run-on transcription rates in isolated nuclei. The results revealed a 3-fold increase in TfR gene transcription and a 6-fold rise in nuclear TfR RNA reaching its steady-state level within 2 h. The main accumulation of mature mRNA in the cytoplasm occurred after 6 h in parallel with the activation of IRF. However, stimulation of IRF binding activity by the iron chelator desferrioxamine, in the absence of IL-2, failed to induce TfR mRNA. Moreover, deprivation of growing B6.1 cells of IL-2 resulted in cell arrest and a rapid decay of TfR mRNA, which was not prevented by the activation of IRF with desferrioxamine. TfR mRNA stabilization appears, therefore, to depend on IL-2. We conclude that TfR mRNA expression is controlled by at least three steps at the onset of cell proliferation: (i) the growth factor-dependent activation of transcription; (ii) mRNA stabilization by IRF in the cytoplasm; and (iii) an additional IL-2-dependent activity which prevents TfR mRNA degradation. Our results indicate that expression of TfR, like ferritin, is controlled by both iron and cytokines.

Animals↗
PubMed1991

Post-transcriptional regulation of the transferrin receptor and 4F2 antigen heavy chain mRNA during growth activation of spleen cells.

The expression of several cell surface proteins including the transferrin receptor and 4F2 antigen is induced when quiescent cells are activated and proliferate. We have studied this induction in mouse spleen cells after stimulation with 4 beta-phorbol 12-myristate 13-acetate (PMA), the Ca(2+)-ionophore, ionomycin and recombinant interleukin-2 (IL-2). The 4F2 antigen heavy chain and transferrin receptor mRNA were barely detectable in resting cells, but increased 60-fold within 4 h of growth stimulation. The corresponding proteins became measurable at the cell surface after 6 h, prior to the S phase. In run-on transcription assays the transferrin receptor gene was transcribed to almost the same extent in resting and growth-stimulated cell populations and the 4F2 antigen heavy chain gene was induced fivefold. This suggests that post-transcriptional control mechanisms are mainly responsible for the accumulation of the respective mRNA at the onset of cell proliferation. In the case of the transferrin receptor, the induction correlated with an activation of the mRNA-binding iron-regulatory factor which is known to increase the stability of the cytoplasmic transferrin receptor mRNA.

Animals↗
PubMed1991

Frequent detection of Epstein-Barr virus DNA by the polymerase chain reaction in lymph node biopsies from patients with Hodgkin's disease without genomic evidence of B- or T-cell clonality.

This study of 52 Swiss patients with Hodgkin's disease (HD), including 17 cases with a high content of Sternberg-Reed (SR) and Hodgkin (H) cells, was performed to determine the percentage of cases harboring Epstein-Barr virus (EBV) DNA and/or clonal rearrangements of Ig and T-cell antigen receptor (TcR) genes in diagnostic lymph node biopsies. Special attention was drawn to the heavily infiltrated cases to detect a possible relationship between clonality and EBV DNA identification. EBV DNA was detected by the polymerase chain reaction (PCR) using three different sets of specific primers. The viral origin of the amplification products was confirmed by hybridization with a radiolabeled internal probe or demonstration of a specific Sma I restriction site. Genomic rearrangement of Ig and TcR genes was studied by Southern blot analysis. EBV DNA was identified by PCR in 38 of 48 cases (79%). Clonal rearrangements were identified in only 4 of 52 cases (Ig genes) and were independent of the degree of infiltration by SR cells and the presence of EBV DNA. The absence of EBV DNA in three cases with numerous SR cells (only one of them showed clonal rearrangement) and the presence of only a few viral copies in four further cases with numerous SR cells (semiquantitative analysis of viral DNA by PCR was performed in 26 EBV-positive cases) suggests that this virus is modulating rather than an etiologic agent in a considerable proportion of HD cases.

B-Lymphocytes↗
PubMed1987

Primary structure of the human 4F2 antigen heavy chain predicts a transmembrane protein with a cytoplasmic NH2 terminus.

The human cell surface antigen 4F2 is a disulfide-linked heterodimer consisting of a glycosylated heavy chain and a nonglycosylated light chain. The antigen is ubiquitously expressed on proliferating cells but only in resting cells from certain tissues. Its function has been proposed to relate to cellular Ca2+/Na+ exchange. We describe the molecular cloning of the 4F2 heavy chain gene and cDNA by a gene transfer approach. Part of the gene was isolated from a genomic lambda library constructed with DNA of a secondary transfectant L cell line that expresses 4F2 antigen. A gene-specific probe derived from the phage inserts was used to isolate two full length cDNA clones. Both cDNA clones directed the expression of 4F2 antigen in transfected mouse L cells. The 4F2 antigen heavy chain gene specifies a 2.1-kilobase mRNA with an open reading frame coding for a 529-residue protein of 58 kDa. The protein lacks an NH2-terminal signal peptide but contains an internal transmembrane-spanning region and four potential glycosylation sites in its COOH-terminal domain. We predict that the 4F2 antigen heavy chain is a transmembrane protein with a cytoplasmic NH2 terminus of 81 amino acids. The antigen shows no homology to known protein sequences.

Amino Acid Sequence↗