Importancia biológica de los telómeros / Biological importance of telomeres

Se exponen los hallazgos históricos y la importancia biológica de los telómeros en la vida celular y en los aspectos genéticos del ADN humano. (AU)

The discovery and the biological importance of the telomeres are exposed. (AU)

Intrinsically bent DNA in replication origins and gene promoters

Intrinsically bent DNA is an alternative conformation of the DNA molecule caused by the presence of dA/dT tracts, 2 to 6 bp long, in a helical turn phase DNA or with multiple intervals of 10 to 11 bp. Other than flexibility, intrinsic bending sites induce DNA curvature in particular chromosome regions such as replication origins and promoters. Intrinsically bent DNA sites are important in initiating DNA replication, and are sometimes found near to regions associated with the nuclear matrix. Many methods have been developed to localize bent sites, for example, circular permutation, computational analysis, and atomic force microscopy. This review discusses intrinsically bent DNA sites associated with replication origins and gene promoter regions in prokaryote and eukaryote cells. We also describe methods for identifying bent DNA sites for circular permutation and computational analysis.

Laminopathies: multiple disorders arising from defects in nuclear architecture.

Lamins are the major structural proteins of the nucleus in an animal cell. In addition to being essential for nuclear integrity and assembly, lamins are involved in the organization of nuclear processes such as DNA replication, transcription and repair. Mutations in the human lamin A gene lead to highly debilitating genetic disorders that primarily affect muscle, adipose, bone or neuronal tissues and also cause premature ageing syndromes. Mutant lamins alter nuclear integrity and hinder signalling pathways involved in muscle differentiation and adipocyte differentiation, suggesting tissue-specific roles for lamins. Furthermore, cells expressing mutant lamins are impaired in their response to DNA damaging agents. Recent reports indicate that certain lamin mutations act in a dominant negative manner to cause nuclear defects and cellular toxicity, and suggest a possible role for aberrant lamins in normal ageing processes.

Cell cycle, DNA replication, repair, and recombination in the dimorphic human pathogenic fungus Paracoccidioides brasiliensis

DNA replication, together with repair mechanisms and cell cycle control, are the most important cellular processes necessary to maintain correct transfer of genetic information to the progeny. These processes are well conserved throughout the Eukarya, and the genes that are involved provide essential information for understanding the life cycle of an organism. We used computational tools for data mining of genes involved in these processes in the pathogenic fungus Paracoccidiodes brasiliensis. Data derived from transcriptome analysis revealed that the cell cycle of this fungus, as well as DNA replication and repair, and the recombination machineries, are highly similar to those of the yeast Saccharomyces cerevisiae. Among orthologs detected in both species, there are genes related to cytoskeleton structure and assembly, chromosome segregation, and cell cycle control genes. We identified at least one representative gene from each step of the initiation of DNA replication. Major players in the process of DNA damage and repair were also identified.

Elimination of polyomavirus origin of replication in constructions with two regulatory regions

Diseñamos un genoma con dos regiones reguladoras (no codificantes) del virus del polima, para estudiar secuencias específicas que tengan alguna función en la expresión genética. Uno de los elementos funciona como "cassette", puede ser escindido de la molécula recombinante, mutado y reinsertado, permitiendo evaluar el efecto de las mutaciones. El fragmento clonado contiene las secuencias correspondientes del nucleótido 5090 al 85 y contiene el ORI, la mayoría de los sitios 5' de iniciación de la transcipción y las secuencias que se sospecha deben conformar el promotor tardío (careciendo del líder). En este estudio demostramos que el sistema funciona si ambas regiones se sitúan en repetición directa, ya que si se localizan en orientación opuesta el virus no es viable en células de ratón. También demostramos que cuando se presenta una mutación en el tramo rico en timinas, se logra la replicación, pero el genoma es inestable ya que elimina la porción de DNA reinsertada. Concluimos de estos estudios que se puden insertar secuencias no codificadoras de Py por duplicado en la región del potenciador sin que se altere la viabilidad viral; esto es, las clonas que presentan ambas regiones reguladoras dispuestas en tándem son infectivas, por lo que consideramos que este sistema puede ser útil en la evaluación de secuencias mutadas detectando si dicha unidad alterada es eliminada

Ciclo celular: mecanismos reguladores e marcadores bioquímicos / Cell cycle: regulatory mechanisms and biochemical markers

Os mecanismos reguladores do ciclo celular e sua inter-relaçäo com fatores de crescimento, oncogenes e anti-oncogenes têm se constiruído nas áreas de maior avanço no estudo da biologia do câncer. Continuamente estäo sendo descobertas novas proteinas no complexo mecanismo que desencadeia as diferentes fases do ciclo celo celular, como também os seus mecanismos de ativaçäo. A descoberta dessas proteínas e co-fatores que regulam as transiçöes G1/s e G2/M e que atuam na replicaçäo do material bem como o papel dos proto-oncogenes dentro do ciclo celular permitiu aumentar o conhecimento sobre as células ciclizantes como também, permitiu que estas pudessem ser detectadas mesmo sem a visualizaçäo de figuras mitóticas. O desenvolvimento de anticorpos monoclonais contra estas proteínas tornou viável o estudo, em larga escala, de taxas de proliferaçäo celular em diferentes neoplasias, uma vez que substâncias como Ki67, polimerase alfa e PCNA - Ciclina somente säo expressas em células em proliferaçäo. A detecçäo de células proliferativas permite, através de sua contagem, estimar as taxas do c rescimento neoplásico com conseqüente repercussäo no prognóstico da doença e na terapêutica do paciente. Neste artigo säo revistos os mecanismos de controle do ciclo celular bem como os métodos de detecçäo de células proliferativas, enfatizando a aplicaçäo de marcadores pela sua praticidade e confiabilidade

Replicative activity of X-chromosome and autosomes of Drosophila melanogaster in autosomal hyperploids and the problem of dosage compensation.

Replicative behaviour of two hyperploid autosomal arms (2L and 3L) of D. melanogaster has been analysed by 3H-thymidine autoradiography. Results reveal that hyperploid autosomal arms (2L-trisomy or 3L-trisomy) replicate synchronously with other disomic non-homologous chromosome arms i.e. there is no asynchrony in the initial mid or late phase of replication patterns between the trisomic 2L or trisomic 3L and disomic arms, suggesting that the extra dose of an autosomal arm can not alter the inherent pattern of replication of that arm. Results further reveal that 2L-trisomy or 3L-trisomy does not impart any influence on X-chromosomal replication in either sex. It is suggested from these results that change in the genomic dose of autosome does not play any role in modulating the replicative organization of the autosomes, 2L and 3L. Thus, although a regulatory mechanism of autosomal dosage compensation does exist for Drosophila, the hierarchy of genetic programming of regulation for X-chromosomal and autosomal dosage compensation might be different. Neither hypertranscriptive activity nor faster replication pattern of the male X-chromosome is influenced by 2L- or 3L-trisomy.

DNA sequence amplification in sciarid flies: results and perspectives

The discovery of Dna sequence amplification in sciarid flies and investigations into its control and biological significance are reviewed. Results thus far show that amplification of specific salivary gland polytene chromosome bands is a general phenomenon in sciarids. It brought about as part of a final endoreplication cycle by the rising titer of ecdysterone that occurs as the Larvae approach the prepupal period. Amplification and transcription of these bands is a late, multistep effect of this hormone.The Dna puffs which form in amplified region produce mRNAs which are translated into polypeptides that appear to be involved in coccon formation. Application of molecular cloning techniques to the study of Dna amplification has allowed precise quantitation of amplification for several Dna puffs and is yielding maps of their transcription units.These techniques will ultimately help to define the origins of Dna puff replication and contribute to an understanding of the mechanism and control of the amplification phenomenon in sciaridae. Projections for future experimental approaches are presented