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Search Results: 1 - 10 of 471900 matches for " María Teresa Parra "
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Algunas reflexiones sobre el consentimiento informado Some reflections on the informed consent
María Teresa Peralta,Mario Orlando Parra
Revista Colombiana de Obstetricia y Ginecología , 2002,
Abstract:
RASGOS DE ALTERACIóN EN LOS MINERALES DE LAS CENIZAS VOLCáNICAS DEL NORTE DE LA CORDILLERA CENTRAL DE COLOMBIA
FLóREZ M.,MARíA TERESA; PARRA S.,LUIS NORBERTO;
Boletín de Ciencias de la Tierra , 2010,
Abstract: this article tries to show some of the characteristics lazy by the physical and chemical weathering of minerals of present volcanic ashes in the sequence the cedral, located to the north part of the "cordillera central of colombia" range. nevertheless, these minerals do not have equal susceptibility to weathering themselves although they are in the same geochemical atmosphere. the weathering degree depends much on its physicochemical structure, of the fragmental size of tephra, the bioclimatic conditions of the site, the topographic position where they have been deposited and of the conditions of drainage, the presence of the preexisting vegetation is equally influential and the microorganisms, all these factors allow that the minerals of volcanic ashes begin their route of weathering. the outstanding characteristics of weathering but in these minerals are: the 1) physical modification of the surfaces, 2) the increase of the specific superficial area, 3) the modification of the edges and forms of crystals, 4) the extensions of cleavage and, 5) the formation of cracks and occlusions. the final consequence of the weathering is the formation of minerals of low degree of crystallization (allophane, imogolite and ferryhidrite, mainly) and the formation of the andisoils, grounds of enormous importance for agriculture.
El enfoque de género en las noticias de salud
Ruiz,María Teresa; Martín,Marta; La Parra,Daniel; Vives,Carmen; Albaladejo,Manuel;
Gaceta Sanitaria , 2004, DOI: 10.1590/S0213-91112004000800009
Abstract: objectives: to use a gender approach to analyze the content of health-related articles affecting both sexes (cancer, heart attack and smoking) or mainly women (anorexia, domestic violence and abortion), published in newspapers in the 1990s. to provide recommendations for writing news with a gender-sensitive approach. material and methods: analysis of the above-mentioned topics in articles published in the national spanish daily newspapers el país, abc and el mundo (1991-1999). data sources: computerized databases of the newspapers. sample of 1358 articles published in the national edition containing selected terms (battering [57], anorexia [79], heart attack [118], abortion [330], smoking [350], cancer [422]). concepts studied: visibility, empowerment and equality. interview with key informers. results: thirty-eight percent of newspaper articles that identified the sex of journalists were signed by women. as the main protagonists of the feature, men (73%) were more visible than women (40%). women mainly appeared as patients (14%) whereas men mainly appeared as politicians (29%) and physicians (24%). conclusions: despite the efforts made in the 1990s, the gender approach in health-related newspaper articles should be increased.
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.
Las políticas de ciencia y tecnología en Venezuela y su impacto en el sistema universitario en el estado Zulia
Parra,María Cristina;
Interciencia , 2007,
Abstract: the policies of science and technology developed by the venezuelan state have been tacitly oriented to surpass the traditional model of production of the knowledge. the unexpected effects of those policies indicate that this model has been strengthened: individualism, isolation, low pertinence and specialization inhibit new models of research. traditionally, the scientific production has had its privileged space in the universities and in them the professors have the key paper in the knowledge production. in the article it is analyzed the possible effect that the policies implemented by the state have had in the reinforcement of a model of production of the knowledge that does not go beyond the academic realm, nor implies the companies, the nongovernmental organizations and communities of direct way. data obtained from a sample of professors of four universities of the zulia region is analyzed: two public institutions and two private ones. the analysis inquires the policies of science and technology of the venezuelan state and challenges to the university institutions and to the own state to evaluate which is the true social impact that the policies have had and to what extent they have meant the democratization of the knowledge.
Rese a de "Galileo, las paradojas del desarrollo" de Orlando Albornoz
María Cristina Parra
Espacio Abierto , 1999,
Abstract:
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.
A High Incidence of Meiotic Silencing of Unsynapsed Chromatin Is Not Associated with Substantial Pachytene Loss in Heterozygous Male Mice Carrying Multiple Simple Robertsonian Translocations
Marcia Manterola equal contributor,Jesús Page equal contributor,Chiara Vasco,Soledad Berríos,María Teresa Parra,Alberto Viera,Julio S. Rufas,Maurizio Zuccotti,Silvia Garagna,Raúl Fernández-Donoso
PLOS Genetics , 2009, DOI: 10.1371/journal.pgen.1000625
Abstract: Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of unsynapsed chromatin (MSUC). Different degrees of asynapsis could contribute to disturb the normal loading of MSUC proteins, interfering with autosome and sex chromosome gene expression and triggering a massive pachytene cell death. We report that in mice that are heterozygous for eight multiple simple Robertsonian translocations, most pachytene spermatocytes bear trivalents with unsynapsed regions that incorporate, in a stage-dependent manner, proteins involved in MSUC (e.g., γH2AX, ATR, ubiquitinated-H2A, SUMO-1, and XMR). These spermatocytes have a correct MSUC response and are not eliminated during pachytene and most of them proceed into diplotene. However, we found a high incidence of apoptotic spermatocytes at the metaphase stage. These results suggest that in Robertsonian heterozygous mice synapsis defects on most pachytene cells do not trigger a prophase-I checkpoint. Instead, meiotic impairment seems to mainly rely on the action of a checkpoint acting at the metaphase stage. We propose that a low stringency of the pachytene checkpoint could help to increase the chances that spermatocytes with synaptic defects will complete meiotic divisions and differentiate into viable gametes. This scenario, despite a reduction of fertility, allows the spreading of Robertsonian translocations, explaining the multitude of natural Robertsonian populations described in the mouse.
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