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M Torres

Publications and source records attributed to M Torres.

At least 37 records · Page 2Linked to original sources
PubMed2003

Quasiperiodic Bloch-like states in a surface-wave experiment.

Bloch-like surface waves associated with a quasiperiodic structure are observed in a classic wave propagation experiment which consists of pulse propagation with a shallow fluid covering a quasiperiodically drilled bottom. We show that a transversal pulse propagates as a plane wave with quasiperiodic modulation, displaying the characteristic undulatory propagation in this quasiperiodic system and reinforcing the idea that analogous concepts to Bloch functions can be applied to quasicrystals under certain circumstances.

Journal Article↗
PubMed2002

A multigrid approach to the average lattices of quasicrystals.

An average structure associated with a given quasilattice is a system composed of several average lattices that in reciprocal space produces strong main reflections. The average lattice of a quasicrystal is a useful concept closely related to the geometric description of the quasicrystal to crystal transformation and has been proved to be structurally significant. Here we calculate average structures for arbitrary two- and three-dimensional quasilattices using the dual generalized method. Additionally, closed analytical expressions for the coordinates of the average structure, the quasiperiodic lattice and its diffraction pattern are given.

Journal Article↗
PubMed2002

Turing patterns with pentagonal symmetry.

We explore numerically the formation of Turing patterns in a confined circular domain with small aspect ratio. Our results show that stable fivefold patterns are formed over a well defined range of disk sizes, offering a possible mechanism for inducing the fivefold symmetry observed in early development of regular echinoids. Using this pattern as a seed, more complex biological structures can be mimicked, such as the pigmentation pattern of sea urchins and the plate arrangements of the calyxes of primitive camerate crinoids.

Journal Article↗
PubMed2002

Regularity in irregular echinoids.

Using the mathematical concept of eutactic star, we prove that it is possible to define a morphospace for irregular echinoids by using a single parameter. In particular, we have found an extraordinary geometric property in the flower-like patterns of the five ambulacral petals of these animals. This property is fulfilled with great accuracy for a large collection of fossil specimens and provides new insights in the study of the viable skeletal designs of extinct and/or living organisms.

Animals↗
PubMed2002

Analysis of BRCA1 and BRCA2 in breast and breast/ovarian cancer families shows population substructure in the Iberian peninsula.

An estimated 5-10% of all breast and ovarian cancers are due to an inherited predisposition, representing a rather large number of patients. In Spain 1/13-1/14 women will be diagnosed with breast cancer during their lifetime. Two major breast cancer genes, BRCA1 and BRCA2, have been identified. To date, several hundred pathogenic mutations in these two genes have been published or reported to the Breast Cancer Information Core, BIC database (http://www.nhgri.nih.gov/Intramural_research_Lab transfer/Bic/index.html). In the present study, 30 Spanish breast and breast/ovarian cancer families (29 from Galicia, NW Spain, and 1 from Catalonia, NE Spain) were screened for mutations in the BRCA1 and BRCA2 genes. The analysis of these genes was carried out by SSCP for shorter exons and direct sequencing in the case of longer ones. Mutations were found in 8 of the 30 families studied (26.66%). It is important to note that all mutations were detected within the BRCA1 gene: 330 A>G, 910_913delGTTC, 2121 C>T, 3958_3962delCTCAGinsAGGC, and 5530 T>A. The BRCA1 330 A>G mutation was found in four unrelated families and accounted for 50% of all identified mutations.

Adult↗
PubMed2002

[Acquired and inherited hypercoagulability among patients with cerebral venous thrombosis].

BACKGROUND: Cerebral venous thrombosis (CVT) is considered to be a relative unusual pathology, probably underdiagnosed. Many acquired and inherited hypercoagulability states (HS) have been described as cause of CVT. OBJECTIVE: [corrected] We evaluated the incidence of acquired and inherited thrombophilic risk factors in a population of CVT patients. METHODS: Hypercoagulability studies were to carried out for patients suffering from radiologically confirmed CVT during a 3 year period (1998-2000). Prothrombin time, aPTT, protein C, protein S and antithrombin III activities, screening and confirmatory tests for lupus anticoagulant (LA), and activated protein C resistance (APCR) were tested. Genetic tests for G1691A factor V (Factor V Leiden), G20210A prothrombin and C677T methylentetrahidrofolate reductase (MTHFR) were performed. Computer database was used for descriptive statistics. RESULTS: 16 patients with CVT (M/F, 6/10) were screened for inherited and acquired coagulation disorders. Mean age of 23.66 years with standard desviation of 19.74 years. Two older patients had antecedents of thrombosis (ischemic stroke and deep-vein thrombosis in leg). We found 1 heterocygosis factor V Leiden associated to LA, 2 heterocygosis G20210A prothrombin (one associated to LA), 2 homocygosis C677T MTHFR, 1 hereditary antithrombin III deficiency and 4 LA. COMMENTS: Although this is a small series, we found a high incidence of hereditary (37.5%) and acquired (37.5%) thrombophilia in patients with CVT.

Adolescent↗
PubMed2001

Chromosome-12 mapping of late-onset Alzheimer disease among Caribbean Hispanics.

Linkage to chromosome 12p for familial Alzheimer disease (AD) has been inconsistent. Using 35 markers near the centromere of chromosome 12, we investigated 79 Caribbean Hispanic families with AD. Two-point linkage analysis using affected sib pairs yielded LOD scores of 3.15 at D12S1623 and 1.43 at D12S1042. The LOD score at D12S1623 decreased to 1.62 in families with late-onset (age >65 years) AD (LOAD), but the LOD score at D12S1042 was unchanged. Among families negative for the apolipoprotein E (APOE-epsilon 4) allele, the LOD score for D12S1623 was lower (1.01), whereas that for D12S1042 increased to 1.73. Among families positive for the APOE-epsilon 4 allele, none of the LOD scores reached 1. Multipoint affected-relative-pair analysis showed peaks at D12S1623 (nonparametric linkage [NPL] score 1.52; P=.028) and near D12S1042, at D12S1057 (NPL score 1.57; P=.027). NPL scores for both D12S1623 and D12S1057 increased in families affected with LOAD, but, in APOE-epsilon 4-negative families, only scores for the region flanking D12S1623 remained elevated (NPL score 1.74; P=.013). This study of Caribbean Hispanics with familial AD extends and provides modest evidence of linkage to loci on chromosome 12p. Linkage varied by age at onset of AD and by the presence or absence of the APOE-epsilon 4 allele.

Adult↗
PubMed2001

A founder mutation in presenilin 1 causing early-onset Alzheimer disease in unrelated Caribbean Hispanic families.

CONTEXT: Genetic determinants of Alzheimer disease (AD) have not been comprehensively examined in Caribbean Hispanics, a population in the United States in whom the frequency of AD is higher compared with non-Hispanic whites. OBJECTIVE: To identify variant alleles in genes related to familial early-onset AD among Caribbean Hispanics. DESIGN AND SETTING: Family-based case series conducted in 1998-2001 at an AD research center in New York, NY, and clinics in the Dominican Republic. PATIENTS: Among 206 Caribbean Hispanic families with 2 or more living members with AD who were identified, 19 (9.2%) had at least 1 individual with onset of AD before the age of 55 years. MAIN OUTCOME MEASURE: The entire coding region of the presenilin 1 gene and exons 16 and 17 of the amyloid precursor protein gene were sequenced in probands from the 19 families and their living relatives. RESULTS: A G-to-C nucleotide change resulting in a glycine-alanine amino acid substitution at codon 206 (Gly206Ala) in exon 7 of presenilin 1 was observed in 23 individuals from 8 (42%) of the 19 families. A Caribbean Hispanic individual with the Gly206Ala mutation and early-onset familial disease was also found by sequencing the corresponding genes of 319 unrelated individuals in New York City. The Gly206Ala mutation was not found in public genetic databases but was reported in 5 individuals from 4 Hispanic families with AD referred for genetic testing. None of the members of these families were related to one another, yet all carriers of the Gly206Ala mutation tested shared a variant allele at 2 nearby microsatellite polymorphisms, indicating a common ancestor. No mutations were found in the amyloid precursor protein gene. CONCLUSIONS: The Gly206Ala mutation was found in 8 of 19 unrelated Caribbean Hispanic families with early-onset familial AD. This genetic change may be a prevalent cause of early-onset familial AD in the Caribbean Hispanic population.

Age of Onset↗
PubMed2001

ADP stimulates the respiratory burst without activation of ERK and AKT in rat alveolar macrophages.

Alveolar macrophages (AM) are the first line of defense against infection in the lungs. We previously showed that the production of superoxide and hydrogen peroxide, i.e., the respiratory burst, is stimulated by adenine nucleotides (ADP >> ATP) in rat AM through signaling pathways involving calcium and protein kinase C. Here, we further show that ADP induces a rapid increase in the tyrosine phosphorylation of several proteins that was reduced by the tyrosine kinase inhibitor genistein, which also inhibited the respiratory burst. Interestingly, ADP did not trigger the activation of the mitogen-activated protein kinases ERK1 and ERK2, or that of protein kinase B/AKT, a downstream target of the phosphatidylinositol 3-kinase (PI3K) pathway. This is in contrast to another stimulus of the respiratory burst, zymosan-activated serum (ZAS), which activates both the ERK and PI3K pathways. Thus, this study demonstrates that the receptor for ADP in rat AM is not coupled to the ERK and AKT pathways and, that neither the ERK pathway nor AKT is essential to induce the activation of the NAPDH oxidase by ADP in rat AM while tyrosine kinases appeared to be required. The rate and amount of hydrogen peroxide released by the ADP-stimulated respiratory burst was similar to that produced by ZAS stimulation. The absence of ERK activation after ADP stimulation therefore suggests that hydrogen peroxide is not sufficient to activate the ERK pathway in rat AM. Nonetheless, as hydrogen peroxide was necessary for ERK activation by ZAS, this indicates that, in contrast to ADP, ZAS stimulates a pathway that is targeted by hydrogen peroxide and leads to ERK activation.

Adenosine Diphosphate↗
PubMed2001

Ribosomal protein S4 is a transcription factor with properties remarkably similar to NusA, a protein involved in both non-ribosomal and ribosomal RNA antitermination.

Escherichia coli ribosomal RNA (rRNA) operons contain antitermination motifs necessary for forming terminator-resistant transcription complexes. In preliminary work, we isolated 'antiterminating' transcription complexes and identified four new proteins potentially involved in rRNA transcription antitermination: ribosomal (r-) proteins S4, L3, L4 and L13. We show here that these r-proteins and Nus factors lead to an 11-fold increase in terminator read-through in in vitro transcription reactions. A significant portion of the effect was a result of r-protein S4. We show that S4 acted as a general antitermination factor, with properties very similar to NusA. It retarded termination and increased read-through at Rho-dependent terminators, even in the absence of the rRNA antiterminator motif. High concentrations of NusG showed reduced antitermination by S4. Like rrn antitermination, S4 selectively antiterminated at Rho-dependent terminators. Lastly, S4 tightly bound RNA polymerase in vivo. Our results suggest that, like NusA, S4 is a general transcription antitermination factor that associates with RNA polymerase during normal transcription and is also involved in rRNA operon antitermination. A model for key r-proteins playing a regulatory role in rRNA synthesis is presented.

Bacterial Proteins↗
PubMed2001

Evaluation of three-dimensional microchannel glass biochips for multiplexed nucleic acid fluorescence hybridization assays.

Three-dimensional, flow-through microchannel glass substrates have a potential for enhanced performance, including increased sensitivity and dynamic range, over traditional planar substrates used in medium-density microarray platforms. This paper presents a methodology for the implementation of multiplexed nucleic acid hybridization fluorescence assays on microchannel glass substrates. Fluorescence detection was achieved, in a first instance, using conventional low-magnification microscope objective lenses, as imaging optics whose depth-of-field characteristics match the thickness of the microchannel glass chip. The optical properties of microchannel glass were shown, through experimental results and simulations, to be compatible with the quantitative detection of heterogeneous hybridization events taking place along the microchannel sidewalls, with detection limits for oligonucleotide targets in the low-attomole range.

Base Sequence↗
PubMed2001

Pituitary adenylyl cyclase-activating polypeptide stimulates DNA synthesis but delays maturation of oligodendrocyte progenitors.

The neuropeptide pituitary adenylyl cyclase-activating peptide (PACAP) and one of its receptors (PAC(1)) are expressed in embryonic neural tube, where they appear to regulate neurogenesis and patterning. We now show that PAC(1) gene expression is also present in neonatal rats in the ventricular and subventricular zones and in the optic chiasm, areas that are rich in oligodendrocyte (OL) progenitors (OLP). Because actions of PACAP on OLP have not been reported, we examined the effects of PACAP on the proliferation of purified OLP in culture and on myelinogenesis in cerebellar slices. Northern analyses on total RNA from purified glial cell subtypes revealed an abundant 7 kb hybridizing transcript in OLP, which was confirmed to correspond to the PAC(1) receptor by reverse transcription-PCR. The presence of this receptor was also corroborated by radioligand binding and cAMP assay. In cultured OL, receptor density decreased during maturation but was partially counterbalanced by the appearance of sites that bound both PACAP and the related peptide vasoactive intestinal peptide. PACAP increased DNA synthesis in OLP cultures almost twofold and increased the bromodeoxyuridine-labeling index in O4-positive OLP. PACAP treatment also resulted in decreased sulfate incorporation into sulfatide in cultures of differentiating OL. The PACAP effect on sulfatide synthesis was fully reproduced in a cerebellar explant model. These findings indicate that PACAP may act at two stages during OL development to (1) stimulate proliferation and (2) delay maturation and/or myelinogenesis.

Animals↗
PubMed2001

Mice deficient for spermatid perinuclear RNA-binding protein show neurologic, spermatogenic, and sperm morphological abnormalities.

Spermatid perinuclear RNA-binding protein (SPNR) is a microtubule-associated RNA-binding protein that localizes to the manchette in developing spermatids. The Spnr mRNA is expressed at high levels in testis, ovary, and brain and is present in these tissues in multiple forms. We have generated a gene trap allele of the murine Spnr, named Spnr(+/GT). Spnr(GT/GT) mutants show a high rate of mortality, reduced weight, and an abnormal clutching reflex. In addition to minor anatomical abnormalities in the brain, males exhibit defects in spermatogenesis that include a thin seminiferous epithelium and disorganization of spermatogenesis. Most of the sperm from mutant males display defects in the flagellum and consequently show decreased motility and transport within the oviducts. Furthermore, sperm from mutant males achieve in vitro fertilization less frequently. Our findings suggest that SPNR plays an important role in normal spermatogenesis and sperm function. Thus, the Spnr(GT/GT) mutant male mouse provides a unique model for some human male infertility cases.

Alleles↗
PubMed2001

Assembly of vault-like particles in insect cells expressing only the major vault protein.

Vaults are the largest (13 megadalton) cytoplasmic ribonucleoprotein particles known to exist in eukaryotic cells. They have a unique barrel-shaped structure with 8-fold symmetry. Although the precise function of vaults is unknown, their wide distribution and highly conserved morphology in eukaryotes suggests that their function is essential and that their structure must be important for their function. The 100-kDa major vault protein (MVP) constitutes approximately 75% of the particle mass and is predicted to form the central barrel portion of the vault. To gain insight into the mechanisms for vault assembly, we have expressed rat MVP in the Sf9 insect cell line using a baculovirus vector. Our results show that the expression of the rat MVP alone can direct the formation of particles that have biochemical characteristics similar to endogenous rat vaults and display the distinct vault-like morphology when negatively stained and examined by electron microscopy. These particles are the first example of a single protein polymerizing into a non-spherically, non-cylindrically symmetrical structure. Understanding vault assembly will enable us to design agents that disrupt vault formation and hence aid in elucidating vault function in vivo.

Animals↗
PubMed2001

Ultrasonic wedges for elastic wave bending and splitting without requiring a full band gap.

We present a novel twinned-square periodic structure for ultrasonic wave bending and splitting that does not require the existence of a complete band gap and plays the role of an ultrasonic wedge. The device allows 45 degrees bending of waves and by adequately switching the twinned structure to an ultrasonic crystal 90 degrees bending is achieved. An extreme refraction law at the grain boundaries is experimentally observed.

Journal Article↗