Transcription as a Threat to Genome Integrity

Genomes undergo different types of sporadic alterations, including DNA damage, point mutations, and genome rearrangements, that constitute the basis for evolution. However, these changes may occur at high levels as a result of cell pathology and trigger genome instability, a hallmark of cancer and a number of genetic diseases. In the last two decades, evidence has accumulated that transcription constitutes an important natural source of DNA metabolic errors that can compromise the integrity of the genome. Transcription can create the conditions for high levels of mutations and recombination by its ability to open the DNA structure and remodel chromatin, making it more accessible to DNA insulting agents, and by its ability to become a barrier to DNA replication. Here we review the molecular basis of such events from a mechanistic perspective with particular emphasis on the role of transcription as a genome instability determinant

Transcription-mediated replication hindrance: a major driver of genome instability

Genome replication involves dealing with obstacles that can result from DNA damage but also from chromatin alterations, topological stress, tightly bound proteins or non-B DNA structures such as R loops. Experimental evidence reveals that an engaged transcription machinery at the DNA can either enhance such obstacles or be an obstacle itself. Thus, transcription can become a potentially hazardous process promoting localized replication fork hindrance and stress, which would ultimately cause genome instability, a hallmark of cancer cells. Understanding the causes behind transcription–replication conflicts as well as how the cell resolves them to sustain genome integrity is the aim of this review

An Array of Layers in Silicon Sulfides: Chain-like and Ground State Structures

While much is known about isoelectronic materials related to carbon nanostructures, such as boron nitride layers and nanotubes, rather less is known about equivalent silicon based materials. Following the recent discovery of phosphorene, we herein discuss isoelectronic silicon monosulfide monolayers. We describe a set of anisotropic ground state structures that clearly have a high stability with respect to the near isotropic silicon monosulfide monolayers. The source of the layer anisotropy is related to the presence of Si-S double chains linked by some Si-Si covalent bonds, which lye at the core of the increased stability, together with a remarkable spd hybridization on Si. The involvement of d orbitals brings more variety to silicon-sulfide based nanostructures that are isoelectronic to phosphorene, which could be relevant for future applications, adding extra degrees of freedom.Comment: 16 pages, 6 figure

Substitutional 4d and 5d Impurities in Graphene

We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The binding energy and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which is also well-known characteristic of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar binding energies, distances and magnetic moments to 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3$\mu_{B}$ for manganese is reduced to 1$\mu_{B}$ for technetium and rhenium. We find that with compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different is 4d or 5d impurities are used instead of 3d impurities.Comment: 16 pages, 4 figure

Gene gating at nuclear pores prevents the formation of R loops

Transcription is an important source of genetic variability. A large amount of transcription-associated genome variation arises from the unscheduled formation of R loops. We have recently found that physical proximity of chromatin to nuclear pores prevents the formation of pathological R loops during transcription. Our study opens new perspectives to understand genome stability as a function of nuclear location

Rpd3L and Hda1 histone deacetylases facilitate repair of broken forks by promoting sister chromatid cohesion

Genome stability involves accurate replication and DNA repair. Broken replication forks, such as those encountering a nick, lead to double strand breaks (DSBs), which are preferentially repaired by sister-chromatid recombination (SCR). To decipher the role of chromatin in eukaryotic DSB repair, here we analyze a collection of yeast chromatin-modifying mutants using a previously developed system for the molecular analysis of repair of replication-born DSBs by SCR based on a mini-HO site. We confirm the candidates through FLP-based systems based on a mutated version of the FLP flipase that causes nicks on either the leading or lagging DNA strands. We demonstrate that Rpd3L and Hda1 histone deacetylase (HDAC) complexes contribute to the repair of replication-born DSBs by facilitating cohesin loading, with no effect on other types of homology-dependent repair, thus preventing genome instability. We conclude that histone deacetylation favors general sister chromatid cohesion as a necessary step in SCR

Complex Chromosomal Rearrangements Mediated by Break-Induced Replication Involve Structure-Selective Endonucleases

This is an open-access article distributed under the terms of the Creative Commons Attribution License.DNA double-strand break (DSB) repair occurring in repeated DNA sequences often leads to the generation of chromosomal rearrangements. Homologous recombination normally ensures a faithful repair of DSBs through a mechanism that transfers the genetic information of an intact donor template to the broken molecule. When only one DSB end shares homology to the donor template, conventional gene conversion fails to occur and repair can be channeled to a recombinationdependent replication pathway termed break-induced replication (BIR), which is prone to produce chromosome nonreciprocal translocations (NRTs), a classical feature of numerous human cancers. Using a newly designed substrate for the analysis of DSB–induced chromosomal translocations, we show that Mus81 and Yen1 structure-selective endonucleases (SSEs) promote BIR, thus causing NRTs. We propose that Mus81 and Yen1 are recruited at the strand invasion intermediate to allow the establishment of a replication fork, which is required to complete BIR. Replication template switching during BIR, a feature of this pathway, engenders complex chromosomal rearrangements when using repeated DNA sequences dispersed over the genome. We demonstrate here that Mus81 and Yen1, together with Slx4, also promote template switching during BIR. Altogether, our study provides evidence for a role of SSEs at multiple steps during BIR, thus participating in the destabilization of the genome by generating complex chromosomal rearrangements.This work was funded by grants from the Spanish Ministry of Science and Innovation (BFU2006-05260, BFU2010-16370, and Consolider Ingenio 2010 CSD2007-015), Junta de Andalucía (BIO-102 and CVI-4567), and the European Union (FEDER). BP was supported by fellowships from Fondation Recherche Médicale (SPE20061209019) and EMBO (1003-2006) and a contract of the Juan de la Cierva Program of the Spanish Ministry of Science and Innovation (JCI 2009-04101).Peer reviewe

Matrimonios entre personas del mismo sexo celebrados en el extranjero y sus efectos jurídicos en Chile. Análisis crítico del artículo 80 de la Ley de Matrimonio Civil

During the reform process to the Civil Marriage Law of 1884, our legislator decided to enact a provision in order to expressly deprive of legal effects any and all same sex marriages celebrated under a foreign jurisdiction. This paper emphasizes the consequences derived from the current legislation –considering that marriage is a cornerstone legal and social institution which transcends the restricted family sphere– in order to further analyze the implications that this legislative decision presents, from the perspective of family protection. Lastly, this paper also focus on the dissimilar legal treatment regarding breach of prohibitions for celebrating marriages that the law enacts, as well as the contradictions that itself presents with those cases in which the very Chilean law limits its validity claim.Durante el proceso de reforma de la ley de matrimonio civil de 1884 se decidió por nuestro legislador la incorporación de una regla destinada expresamente a privar de efectos a los matrimonios celebrados en el extranjero, cuando los cónyuges sean del mismo sexo, el artículo 80 de la Ley Nº 19.947. En el presente trabajo se pondrá énfasis en las consecuencias que se derivan de la actual regulación –considerando que el matrimonio es una institución que ocupa un lugar central en nuestro ordenamiento– cuya importancia trasciende el ámbito estrictamente familiar, con el fin de analizar las implicancias que presenta esta decisión legislativa desde la perspectiva de la protección de la familia. Finalmente, se destacarán su disímil tratamiento frente a la infracción de las prohibiciones de celebración del matrimonio establecidas por la misma ley y las contradicciones que presenta con aquellos casos donde la propia ley chilena limita su pretensión de aplicación

Validación de un sistema de transporte para medicamentos con control de temperatura.

Tesis (Químico Farmacéutico)En la actualidad, los laboratorios farmacéuticos buscan validar sus procesos pertenecientes a la línea de fabricación de sus productos, con la finalidad de establecer un alto grado de seguridad, dejando en evidencia que el proceso se efectuó uniformemente, en conformidad con los resultados esperados. Siendo la distribución de los productos, parte de los procesos de fabricación, no se han elaborado directrices específicas para realizar su validación. Esto podría deberse a las diversas variables que limitan el poder demostrar que el proceso sea uniforme o por presentar tan nivel de dinamismo, que dificulta confeccionar una metodología adecuada para validar un sistema de transporte o distribución. Por esta razón, organismos gubernamentales como el Ministerio de Salud (MINSAL) y el Instituto de Salud Púbica (ISP) han incrementado su interés en promulgar diversas directrices para la distribución de productos que requieren un control de temperatura. En función de ello, se realizaron los estudios y protocolos necesarios para validar un sistema de transporte para productos farmacéuticos que requieren control de temperatura

Human mitochondrial degradosome prevents harmful mitochondrial R loops and mitochondrial genome instability

R loops are nucleic acid structures comprising an DNA-RNA hybrid and a displaced single-stranded DNA. These structures may occur transiently during transcription, playing essential biological functions. However, persistent R loops may become pathological as they are important drivers of genome instability and have been associated with human diseases. The mitochondrial degradosome is a functionally conserved complex from bacteria to human mitochondria. It is composed of the ATP-dependent RNA and DNA helicase SUV3 and the PNPase ribonuclease, playing a central role in mitochondrial RNA surveillance and degradation. Here we describe a new role for the mitochondrial degradosome in preventing the accumulation of pathological R loops in the mitochondrial DNA, in addition to preventing dsRNA accumulation. Our data indicate that, similar to the molecular mechanisms acting in the nucleus, RNA surveillance mechanisms in the mitochondria are crucial to maintain its genome integrity by counteracting pathological R-loop accumulation.European Research Council ERC2014 AdG669898 TARLOOPMinisterio de Economía y Competitividad BFU2013-42918-P, BFU2016-75058-