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Search Results: 1 - 10 of 512422 matches for " José A. Suja "
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Espinoza,Omar; Bustos-Obregón,Eduardo; Suja,José A;
Revista chilena de anatomía , 2002, DOI: 10.4067/S0716-98682002000100005
Abstract: chemical environmental pollution is a major problem at present. agropesticides are relevant in this regard, since they affect human and animal health (draper, 1985; rodríguez & bustos-obregón, 2000). parathion" (pt), an organophosphorate pesticide inhibits acetylcholinesterase and is metabolized in liver, lung and brain. it is transformed in paraoxon (po), its active metabolite (chambers & chambers, 1990 and siller et al., 1997). this work analizes the effect of a single dose of pt on the apoptotic index of cf1 mouse hepatocytes. male cf1 mice (8 to 10 weeks old, average weight of 30 g) were treated with a single injection of pt, of 20 mg/kg body weight (sobarzo & bustos-obregón, 2000). the animals were sacrificed at 1, 8, 16, 28 and 50 days after injection. histological analysis of hepatic tissue was done by light microscopy for counting of apoptotic (and binucleated) cells in he stained slides. it has been postulated that pt is carcinogenic and that it modifies the ability of hepatocytes to regenerate (metcalfe & streuli, 1997 and fausto, 2000). we conclude that pt is cytotoxic even at low concentrations, since it increases apoptosis and affects the normal homeostasis of the hepatic tissue
Omar Espinoza,Eduardo Bustos-Obregón,José A Suja
Revista chilena de anatomía , 2002,
Abstract: En las últimas décadas el uso masivo de agropesticidas órganofosforados, como Parathion y Malathion, ha permitido el control de plagas en la producción hortofrutícola, mejorando la productividad e incrementando la oferta de alimentos de mayor calidad. Sin embargo, pese a su efectividad, estos compuestos químicos son potenciales causantes de da os morfológicos y genéticos, de alto riesgo para la Salud Humana y animal (Draper, 1985; Rodríguez y Bustos-Obregón, 2000). El parathion" (PT), inhibidor de la acetilcolinesterasa, se metaboliza en hígado, pulmón y cerebro. El efecto tóxico se debe a un proceso de desulfuración oxidativa hepática, que transforma el PT en paraoxon (PO), siendo éste su metabolito activo (Chambers y Chambers, 1990; Siller et al., 1997). El objetivo del presente trabajo es evaluar los efectos de una dosis única de PT sobre los índices de apoptosis en hepatocitos de ratón CF1. Se usaron ratones macho CF1 de 8 a 10 semanas, con un peso promedio de 30 g, a los cuales se les aplicó una dosis intraperitoneal única de PT de 20 mg/Kg de peso (Sobarzo y Bustos-Obregón, 2000). Posteriormente fueron sacrificados a 1, 8, 16, 28 y 50 días postratamiento. El análisis histológico del hígado se realizó mediante microscopía óptica sobre cortes te idos con hematoxilina/eosina en que se analizó la presencia y frecuencia de hepatocitos apoptóticos. Los resultados obtenidos permiten demostrar el efecto del PT sobre el hepatocito con un aumento estadísticamente significativo de apoptosis. Se postula que el PT es carcinogénico, que bloquea o modifica la capacidad de replicación de los hepatocitos, alterando la susceptibilidad del tejido hepático (Fausto, 2000; Metcalfe y Streuli, 1997). Se concluye que el PT tiene un efecto tóxico, aún en dosis consideradas bajas, aumentando significativamente los índices de eventos apoptóticos, alterando el ciclo celular y afectando la histofisiología del tejido hepático Chemical environmental pollution is a major problem at present. Agropesticides are relevant in this regard, since they affect human and animal health (Draper, 1985; Rodríguez & Bustos-Obregón, 2000). Parathion" (PT), an organophosphorate pesticide inhibits acetylcholinesterase and is metabolized in liver, lung and brain. It is transformed in paraoxon (PO), its active metabolite (Chambers & Chambers, 1990 and Siller et al., 1997). This work analizes the effect of a single dose of PT on the apoptotic index of CF1 mouse hepatocytes. Male CF1 mice (8 to 10 weeks old, average weight of 30 g) were treated with a single injection of PT, of 20 mg/Kg body weight (
Condensin I Reveals New Insights on Mouse Meiotic Chromosome Structure and Dynamics
Alberto Viera, Rocío Gómez, María T. Parra, John A. Schmiesing, Kyoko Yokomori, Julio S. Rufas, José A. Suja
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000783
Abstract: Chromosome shaping and individualization are necessary requisites to warrant the correct segregation of genomes in either mitotic or meiotic cell divisions. These processes are mainly prompted in vertebrates by three multiprotein complexes termed cohesin and condensin I and II. In the present study we have analyzed by immunostaining the appearance and subcellular distribution of condensin I in mouse mitotic and meiotic chromosomes. Our results demonstrate that in either mitotically or meiotically dividing cells, condensin I is loaded onto chromosomes by prometaphase. Condensin I is detectable as a fuzzy axial structure running inside chromatids of condensed chromosomes. The distribution of condensin I along the chromosome length is not uniform, since it preferentially accumulates close to the chromosome ends. Interestingly, these round accumulations found at the condensin I axes termini colocalized with telomere complexes. Additionally, we present the relative distribution of the condensin I and cohesin complexes in metaphase I bivalents. All these new data have allowed us to propose a comprehensive model for meiotic chromosome structure.
Sequential Assembly of Centromeric Proteins in Male Mouse Meiosis
María Teresa Parra ,Rocío Gómez,Alberto Viera,Elena Llano,Alberto M. Pendás,Julio S. Rufas,José A. Suja
PLOS Genetics , 2009, DOI: 10.1371/journal.pgen.1000417
Abstract: The assembly of the mitotic centromere has been extensively studied in recent years, revealing the sequence and regulation of protein loading to this chromosome domain. However, few studies have analyzed centromere assembly during mammalian meiosis. This study specifically targets this approach on mouse spermatocytes. We have found that during prophase I, the proteins of the chromosomal passenger complex Borealin, INCENP, and Aurora-B load sequentially to the inner centromere before Shugoshin 2 and MCAK. The last proteins to be assembled are the outer kinetochore proteins BubR1 and CENP-E. All these proteins are not detected at the centromere during anaphase/telophase I and are then reloaded during interkinesis. The loading sequence of the analyzed proteins is similar during prophase I and interkinesis. These findings demonstrate that the interkinesis stage, regularly overlooked, is essential for centromere and kinetochore maturation and reorganization previous to the second meiotic division. We also demonstrate that Shugoshin 2 is necessary for the loading of MCAK at the inner centromere, but is dispensable for the loading of the outer kinetochore proteins BubR1 and CENP-E.
A Perikinetochoric Ring Defined by MCAK and Aurora-B as a Novel Centromere Domain
María Teresa Parra ,Rocío Gómez,Alberto Viera,Jesús Page,Adela Calvente,Linda Wordeman,Julio S Rufas,José A Suja
PLOS Genetics , 2006, DOI: 10.1371/journal.pgen.0020084
Abstract: Mitotic Centromere-Associated Kinesin (MCAK) is a member of the kinesin-13 subfamily of kinesin-related proteins. In mitosis, this microtubule-depolymerising kinesin seems to be implicated in chromosome segregation and in the correction of improper kinetochore-microtubule interactions, and its activity is regulated by the Aurora-B kinase. However, there are no published data on its behaviour and function during mammalian meiosis. We have analysed by immunofluorescence in squashed mouse spermatocytes, the distribution and possible function of MCAK, together with Aurora-B, during both meiotic divisions. Our results demonstrate that MCAK and Aurora-B colocalise at the inner domain of metaphase I centromeres. Thus, MCAK shows a “cone”-like three-dimensional distribution beneath and surrounding the closely associated sister kinetochores. During the second meiotic division, MCAK and Aurora-B also colocalise at the inner centromere domain as a band that joins sister kinetochores, but only during prometaphase II in unattached chromosomes. During chromosome congression to the metaphase II plate, MCAK relocalises and appears as a ring below each sister kinetochore. Aurora-B also relocalises to appear as a ring surrounding and beneath kinetochores but during late metaphase II. Our results demonstrate that the redistribution of MCAK at prometaphase II/metaphase II centromeres depends on tension across the centromere and/or on the interaction of microtubules with kinetochores. We propose that the perikinetochoric rings of MCAK and Aurora-B define a novel transient centromere domain at least in mouse chromosomes during meiosis. We discuss the possible functions of MCAK at the inner centromere domain and at the perikinetochoric ring during both meiotic divisions.
Meiotic Pairing and Segregation of Achiasmate Sex Chromosomes in Eutherian Mammals: The Role of SYCP3 Protein
Roberto de la Fuente,María Teresa Parra,Alberto Viera,Adela Calvente,Rocío Gómez,José ángel Suja,Julio S Rufas,Jesús Page
PLOS Genetics , 2007, DOI: 10.1371/journal.pgen.0030198
Abstract: In most eutherian mammals, sex chromosomes synapse and recombine during male meiosis in a small region called pseudoautosomal region. However in some species sex chromosomes do not synapse, and how these chromosomes manage to ensure their proper segregation is under discussion. Here we present a study of the meiotic structure and behavior of sex chromosomes in one of these species, the Mongolian gerbil (Meriones unguiculatus). We have analyzed the location of synaptonemal complex (SC) proteins SYCP1 and SYCP3, as well as three proteins involved in the process of meiotic recombination (RAD51, MLH1, and γ-H2AX). Our results show that although X and Y chromosomes are associated at pachytene and form a sex body, their axial elements (AEs) do not contact, and they never assemble a SC central element. Furthermore, MLH1 is not detected on the AEs of the sex chromosomes, indicating the absence of reciprocal recombination. At diplotene the organization of sex chromosomes changes strikingly, their AEs associate end to end, and SYCP3 forms an intricate network that occupies the Y chromosome and the distal region of the X chromosome long arm. Both the association of sex chromosomes and the SYCP3 structure are maintained until metaphase I. In anaphase I sex chromosomes migrate to opposite poles, but SYCP3 filaments connecting both chromosomes are observed. Hence, one can assume that SYCP3 modifications detected from diplotene onwards are correlated with the maintenance of sex chromosome association. These results demonstrate that some components of the SC may participate in the segregation of achiasmate sex chromosomes in eutherian mammals.
Sequential Loading of Cohesin Subunits during the First Meiotic Prophase of Grasshoppers
Ana M Valdeolmillos equal contributor,Alberto Viera equal contributor,Jesús Page,Ignacio Prieto,Juan L Santos,María Teresa Parra,Margarete M. S Heck,Carlos Martínez-A,José L Barbero,José A Suja,Julio S Rufas
PLOS Genetics , 2007, DOI: 10.1371/journal.pgen.0030028
Abstract: The cohesin complexes play a key role in chromosome segregation during both mitosis and meiosis. They establish sister chromatid cohesion between duplicating DNA molecules during S-phase, but they also have an important role during postreplicative double-strand break repair in mitosis, as well as during recombination between homologous chromosomes in meiosis. An additional function in meiosis is related to the sister kinetochore cohesion, so they can be pulled by microtubules to the same pole at anaphase I. Data about the dynamics of cohesin subunits during meiosis are scarce; therefore, it is of great interest to characterize how the formation of the cohesin complexes is achieved in order to understand the roles of the different subunits within them. We have investigated the spatio-temporal distribution of three different cohesin subunits in prophase I grasshopper spermatocytes. We found that structural maintenance of chromosome protein 3 (SMC3) appears as early as preleptotene, and its localization resembles the location of the unsynapsed axial elements, whereas radiation-sensitive mutant 21 (RAD21) (sister chromatid cohesion protein 1, SCC1) and stromal antigen protein 1 (SA1) (sister chromatid cohesion protein 3, SCC3) are not visualized until zygotene, since they are located in the synapsed regions of the bivalents. During pachytene, the distribution of the three cohesin subunits is very similar and all appear along the trajectories of the lateral elements of the autosomal synaptonemal complexes. However, whereas SMC3 also appears over the single and unsynapsed X chromosome, RAD21 and SA1 do not. We conclude that the loading of SMC3 and the non-SMC subunits, RAD21 and SA1, occurs in different steps throughout prophase I grasshopper meiosis. These results strongly suggest the participation of SMC3 in the initial cohesin axis formation as early as preleptotene, thus contributing to sister chromatid cohesion, with a later association of both RAD21 and SA1 subunits at zygotene to reinforce and stabilize the bivalent structure. Therefore, we speculate that more than one cohesin complex participates in the sister chromatid cohesion at prophase I.
Involvement of Synaptonemal Complex Proteins in Sex Chromosome Segregation during Marsupial Male Meiosis
Jesús Page,Alberto Viera,María Teresa Parra,Roberto de la Fuente,José ángel Suja,Ignacio Prieto,José Luis Barbero,Julio S Rufas,Soledad Berríos,Raúl Fernández-Donoso
PLOS Genetics , 2006, DOI: 10.1371/journal.pgen.0020136
Abstract: Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions, and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not recombine, they segregate reductionally in anaphase I. We have investigated the nature of sex chromosome association in spermatocytes of the marsupial Thylamys elegans, in order to discern the mechanisms involved in ensuring their proper segregation. We focused on the localization of the axial/lateral element protein SCP3 and the cohesin subunit STAG3. Our results show that X and Y chromosomes never appear as univalents in metaphase I, but they remain associated until they orientate and segregate to opposite poles. However, they must not be tied by a chiasma since their separation precedes the release of the sister chromatid cohesion. Instead, we show they are associated by the dense plate, a SCP3-rich structure that is organized during the first meiotic prophase and that is still present at metaphase I. Surprisingly, the dense plate incorporates SCP1, the main protein of the central element of the synaptonemal complex, from diplotene until telophase I. Once sex chromosomes are under spindle tension, they move to opposite poles losing contact with the dense plate and undergoing early segregation. Thus, the segregation of the achiasmatic T. elegans sex chromosomes seems to be ensured by the presence in metaphase I of a synaptonemal complex-derived structure. This feature, unique among vertebrates, indicates that synaptonemal complex elements may play a role in chromosome segregation.
Hikmat A. Alrawi,Suja Sarah Thomas
Asian Academy of Management Journal , 2007,
Abstract: Although extensively studied in the last two decades, contingency theory has been given relatively little consideration in terms of the factors that influence the accounting information systems. Few organizations appear to have systematic processes in place for managing the evolution of their measurement systems and few researchers appear to have explored two of the main questions: What are the requirements of accounting information in UAE banks? And, how efficient is the accounting systems in UAE banks? The paper addresses these questions by providing empirical evidence of management accounting information contingencies based on a sample of banks in the UAE.
Methods of Battery Charging with Buck Converter Using Soft-Switching Techniques
S. Abinaya,A. Sivaranjani,S. Suja
Bonfring International Journal of Power Systems and Integrated Circuits , 2011,
Abstract: This paper is a detailed study on methods of battery charging with Buck Resonant converter using soft switching techniques like ZVS and ZCS. This study also presents the circuit configuration with the least components to realize a highly efficient solar energy battery charger with a zero-voltage and zero current switching resonant converter. The high-frequency resonant converter has numerous well-known advantages over the traditional hard-switching converters. The most important advantage is that it offers a lower switching loss and a higher power density. Additionally, the soft switching current waveform characterizes a lower electromagnetic interference (EMI). The operating principles and design procedure of the proposed charger with both zero voltage and zero current are thoroughly analyzed. The optimal values of the resonant components are computed by applying the characteristic curve and electric functions derived from the circuit configuration. Finally, a simulation model is implemented for charger circuit designed for a 12-V 4-Ah lead acid battery using zero voltage and zero current switching and MATLAB/SIMULINK software is used as the simulation tool. The proposed dc?dc battery charger has a straightforward structure, low cost, easy control, and high efficiency. Satisfactory performance is obtained from the experimental results.
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