Replicación del rDNA en organismos eucariotas : localizción y caracterización de barreras de replicación

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 9-05-199

Role of cis-regulatory elements on the ring-specific hrp3 promoter in the human parasite Plasmodium falciparum

Identification of promoter elements responsible for regulation of gene expression has been hampered by the AT richness of P. falciparum intergenic regions. Nested deletions of histidine-rich protein 3 (hrp3) promoter suggested the presence of a multipartite ring-specific element. Linker scanning (LS) of this ring-specific promoter showed that the alteration of several promoter regions decreased the luciferase activity compared to the wild-type configuration, indicating that these regions played a role in gene expression. No homology was observed by comparison of putative regulatory elements of other genes identified by bioinformatic analysis with the hrp3 enhancer, implying a different mechanism of gene regulation by the hrp3 promoter. LS and deletion analysis of the 5′ untranslated region (UTR) of the hrp3 suggested that this region contains elements which interact with promoter elements to regulate gene expression. Analysis of the intron in the UTR region suggested that this region does not play a role in stage specificity in the hrp3 promoter. Together, our results indicate the presence of multiple mechanisms of gene regulation in the parasite. © Springer-Verlag 2010

Comparative analysis of stage specific gene regulation of apicomplexan Parasites: Plasmodium falciparum and Toxoplasma gondii

Apicomplexans comprise some of the most life threatening parasites infecting human and livestock and includes Plasmodium and Toxoplasma, the causative agents of malaria and toxoplasmosis respectively, in humans as well as Neospora caninum (abortion in livestock, neosporosis in dogs), Cryptosporidium (Diarrheal cryptosporidiosis and opportunistic infections in AIDS patients) and Eimeria (poultry coccidiosis). These parasites are characterized by a complex life cycle usually alternating between sexual and asexual cycles in different hosts. The need to adapt to different host environments, demands a tight regulation of gene expression during parasite development. Therefore, the understanding of parasite biology will facilitate the control of the infection and the disease. In this review we emphasize the progress made so far in gene regulation in two medically important parasites, namely Plasmodium falciparum and Toxoplasma gondii, as well as other less known apicomplexan. The genome of both Plasmodium and Toxoplasma has been sequenced and since then there has been a significant progress in understanding the molecular mechanisms that control stage specific gene expression in the two parasites. In addition, the information gained in each of the parasite can be used in studying mechanisms that are still elusive in the other apicomplexans that are not readily available. Additionally, they can serve as model systems for other disease causing Apicomplexan parasites. © 2010 Bentham Science Publishers Ltd

Cultura escolar: Una mirada a la cultura de la Escuela Nacional Bárbula I, ubicada en Naguanagua-Estado Carabobo.

La presente investigación tiene como propósito ofrecer una explicación de la rutina escolar desde la visión de los niños y niñas. Según los autores/as consultados la rutina escolar debería estar relacionada con el deber ser que se encuentra enmarcada en el currículo. Esta investigación se encuentra bajo un paradigma post-positivista, por ser un estudio cualitativo y la fenomenología como método. Para la recopilación de la información se utilizó la observación participante como técnica, la cual fue ejecutada durante la estadía en la institución de la mano con los diarios de campo, que sirvieron como instrumento. Además empleamos la técnica de la entrevista con su respectivo guión dirigido a niños/as de la sección “C y D” de la institución. El análisis y la interpretación de los hallazgos fue mediante la comparación de los diarios de campo y la entrevista, de donde emergió coherencia entre lo que se observaba y las opiniones de los niños y niñas de acuerdo a la rutina escolar que viven ellos día a día manifestando la petición de realizar actividades didácticas durante la rutina escolar. Los hallazgos que se evidenciaron fueron el cansancio, aburrimiento, desinterés por las actividades y entre otras. Y como conclusión los niños/as tienen conocimiento del significado de la rutina diaria y los elementos que conlleva, por ende hacen petición para la integración de nuevas estrategias didácticas, juegos, lectura de cuentos y actividades deportivas

Co-localization of polar replication fork barriers and rRNA transcription terminators in mouse rDNA

8 p.-7 fig.We investigated the replication of the region where transcription terminates in mouse rDNA. It contains a replication fork barrier (RFB) that behaves in a polar manner, arresting only replication forks moving in the direction opposite to transcription. This RFB consists of several closely spaced fork arrest sites that co-localize with the transcription terminator elements, known as Sal boxes. Sal boxes are the target for mTTF-I (murine transcription termination factor I). These results suggest that both termination of rRNA transcription and replication fork arrest may share cis-acting as well as trans-acting factors.This work was partially supported by grant PM95-0016 from the Spanish Dirección General de Enseñanza Superior, grant 96/0470 from the Spanish Fondo de Investigación Sanitaria and a fellowship of the Consejo Nacional de Investigaciones Científicas y Tecnológicas (Venezuela) to C.L.-E.Peer reviewe

Plasmodium falciparum: hrp3 promoter region is associated with stage-specificity and episomal recombination

The asexual blood stage of Plasmodium falciparum in the human host is comprised of morphologically distinct ring, trophozoite and schizont stages, each of which possesses a distinct pattern of gene expression. Episomal promoter recombination has been recently reported in malaria parasites. We aim to investigate the nature of this process, and its relationship with promoter activity by employing a series of nested deletions of the ring-specific hrp3 promoter. Our results showed a discrete promoter region that is preferentially used for recombination. The P. falciparum hrp3 mRNA is only seen in ring-stage parasites but deletion of the recombination region was associated with decreased ring-stage expression and concurrent detection of transcripts in trophozoite-stage parasites. Our results describe a ring-stage specific regulatory region possibly involved in episomal promoter recombination, suggesting that common sequences might mediate both processes. © 2007 Elsevier Inc. All rights reserved

Characterization of the pea rDNA replication fork barrier: Putative cis-acting and trans-acting factors

It was previously shown that in pea (Pisum sativum), rDNA repeats contain a polar replication fork barrier that blocks progression of the replication machinery moving in the direction opposite to transcription. This barrier maps in the untranscribed spacer close to the 3\u27 end of the 25S gene. Very similar barriers are also found in the rDNA of yeast, Xenopus and mammalian cultured cells. This high conservation indicates that the rDNA barrier plays a relevant biological role. Progression of replication forks through the DNA sequence where the barrier maps in pea was investigated in plasmids replicating in Escherichia coli and Saccharomyces cerevisiae. No barrier was detected in these heterologous systems, indicating that the DNA sequence by itself was insufficient to block the replication machinery. Therefore, trans-acting factors were likely to be required. Taking advantage of the natural sequence heterogeneity in pea rDNA, we obtained evidence that a 27 bp imperfect tandem repeat is involved in the arrest of replication. Moreover, nuclear protein(s) specifically bound to this repeat suggesting that this DNA/protein complex is responsible for the polar arrest of replication forks