Chk1 inhibits replication factory activation but allows dormant origin firing in existing factories

Replication origins are licensed by loading MCM2-7 hexamers before entry into S phase. However, only ∼10% of licensed origins are normally used in S phase, with the others remaining dormant. When fork progression is inhibited, dormant origins initiate nearby to ensure that all of the DNA is eventually replicated. In apparent contrast, replicative stress activates ataxia telangiectasia and rad-3–related (ATR) and Chk1 checkpoint kinases that inhibit origin firing. In this study, we show that at low levels of replication stress, ATR/Chk1 predominantly suppresses origin initiation by inhibiting the activation of new replication factories, thereby reducing the number of active factories. At the same time, inhibition of replication fork progression allows dormant origins to initiate within existing replication factories. The inhibition of new factory activation by ATR/Chk1 therefore redirects replication toward active factories where forks are inhibited and away from regions that have yet to start replication. This minimizes the deleterious consequences of fork stalling and prevents similar problems from arising in unreplicated regions of the genome

Europe's rare earth element resource potential: an overview of REE metallogenetic provinces and their geodynamic setting

Security of supply of a number of raw materials is of concern for the European Union; foremost among these are the rare earth elements (REE), which are used in a range of modern technologies. A number of research projects, including the EURARE and ASTER projects, have been funded in Europe to investigate various steps along the REE supply chain. This paper addresses the initial part of that supply chain, namely the potential geological resources of the REE in Europe. Although the REE are not currently mined in Europe, potential resources are known to be widespread, and many are being explored. The most important European resources are associated with alkaline igneous rocks and carbonatites, although REE deposits are also known from a range of other settings. Within Europe, a number of REE metallogenetic belts can be identified on the basis of age, tectonic setting, lithological association and known REE enrichments. This paper reviews those metallogenetic belts and sets them in their geodynamic context. The most well-known of the REE belts are of Precambrian to Palaeozoic age and occur in Greenland and the Fennoscandian Shield. Of particular importance for their REE potential are the Gardar Province of SW Greenland, the Svecofennian Belt and subsequent Mesoproterozoic rifts in Sweden, and the carbonatites of the Central Iapetus Magmatic Province. However, several zones with significant potential for REE deposits are also identified in central, southern and eastern Europe, including examples in the Bohemian Massif, the Iberian Massif, and the Carpathians

Stochastic association of neighboring replicons creates replication factories in budding yeast

Peer reviewedPublisher PD

Los estudiantes de medicina españoles y la medicina de familia. Datos de las 2 fases de una encuesta estatal

Objetivo Explorar percepciones y expectativas de estudiantes de los cursos 1.°, 3.° y 5.° de las facultades de medicina sobre medicina de familia y comunitaria (MFyC) y atención primaria (AP). Diseño Estudio observacional con administración de un cuestionario en 2 cortes transversales con un intervalo de 2 años. Emplazamiento Facultades de medicina españolas. Participantes Estudiantes de los cursos 1.°, 3.° y 5.° de 22 facultades (1.a fase) y 15 en la segunda. Mediciones principales Cuestionario autocumplimentado administrado durante el primer trimestre de los cursos 2009-2010 y 2011-2012. Consta de 70 ítems en 3 bloques: percepciones sobre MFyC (19 ítems), formación en MFyC (26 ítems), expectativas y preferencias (25 ítems), más 13 ítems específicos para alumnos de 3.° y 5.°. La mayoría se respondían según una escala Likert (de 1 a 6). Resultados En la 1.a fase se obtuvieron 5.299 cuestionarios y 3.869 en la segunda. Los estudiantes perciben la MFyC y AP como un ámbito esencial del sistema sanitario y de ejercicio profesional pero con escaso atractivo científico-técnico. El 87% consideran necesaria y obligatoria la formación en MFyC y que debería iniciarse en el 3.er curso. Prefieren las especialidades médicas hospitalarias (88-89%) seguidas de las quirúrgicas y la pediatría. La MFyC es preferida por el 37-39%. Al iniciar la carrera solamente entre el 24 y el 28% de los estudiantes tienen una decisión clara sobre la especialidad que van a escoger. Conclusiones La MFyC y la AP son ámbitos esenciales y han de formar parte de los currículum pero tienen una baja consideración científica. Objective: To examine the perceptions and expectations about Family Practice (FP) and Primary Care (PC) in 1st, 3rd and 5th year students in medical schools. Design: An observational study in two cross sections with intervals of two years. Location: Spanish Medical Schools. Participants: 1st, 3rd and 5th year students of 22 schools (1st phase) and 15 (second phase). Primary measurements: Self-report questionnaires completed during the first quarter of the 2009-2010 and 2011-2012 academic years. It had 70 items in three blocks: perceptions of FP (19 items), training in FP (26 items), expectations and preferences (25 items), plus 13 specific items for 3rd and 5th year students. Most of the items were answered in a 6 point Likert scale. Results: A total of 5299 responses in phase I, and 3869 in phase II were received. Students perceive FP and PC as essential areas of the health system and professional practice, but with little scientific and technical appeal. The large majortiy, 87%, consider training in FP necessary and compulsory, and it should start in third year. They prefer hospital medical specialities (88-89%), followed by surgical and paediatrics. FP is preferred by the 37-39%. Only between 24% and 28% of students have a clear preference for a specialty when they start medical studies. Conclusions: FP and PC are key areas and should be part of the curriculum, but are perceived to be of low scientific appeal

DNA topoisomerases participate in fragility of the oncogene RET

Fragile site breakage was previously shown to result in rearrangement of the RET oncogene, resembling the rearrangements found in thyroid cancer. Common fragile sites are specific regions of the genome with a high susceptibility to DNA breakage under conditions that partially inhibit DNA replication, and often coincide with genes deleted, amplified, or rearranged in cancer. While a substantial amount of work has been performed investigating DNA repair and cell cycle checkpoint proteins vital for maintaining stability at fragile sites, little is known about the initial events leading to DNA breakage at these sites. The purpose of this study was to investigate these initial events through the detection of aphidicolin (APH)-induced DNA breakage within the RET oncogene, in which 144 APHinduced DNA breakpoints were mapped on the nucleotide level in human thyroid cells within intron 11 of RET, the breakpoint cluster region found in patients. These breakpoints were located at or near DNA topoisomerase I and/or II predicted cleavage sites, as well as at DNA secondary structural features recognized and preferentially cleaved by DNA topoisomerases I and II. Co-treatment of thyroid cells with APH and the topoisomerase catalytic inhibitors, betulinic acid and merbarone, significantly decreased APH-induced fragile site breakage within RET intron 11 and within the common fragile site FRA3B. These data demonstrate that DNA topoisomerases I and II are involved in initiating APH-induced common fragile site breakage at RET, and may engage the recognition of DNA secondary structures formed during perturbed DNA replication

Increased cortical surface area and gyrification following long-term survival from early monocular enucleation

AbstractPurposeRetinoblastoma is typically diagnosed before 5 years of age and is often treated by enucleation (surgical removal) of the cancerous eye. Here, we sought to characterize morphological changes of the cortex following long-term survival from early monocular enucleation.MethodsNine adults with early right-eye enucleation (≤48 months of age) due to retinoblastoma were compared to 18 binocularly intact controls. Surface area, cortical thickness, and gyrification estimates were obtained from T1 weighted images and group differences were examined.ResultsEarly monocular enucleation was associated with increased surface area and/or gyrification in visual (i.e., V1, inferior temporal), auditory (i.e., supramarginal), and multisensory (i.e., superior temporal, inferior parietal, superior parietal) cortices compared with controls. Visual cortex increases were restricted to the right hemisphere contralateral to the remaining eye, consistent with previous subcortical data showing asymmetrical lateral geniculate nucleus volume following early monocular enucleation.ConclusionsAltered morphological development of visual, auditory, and multisensory regions occurs subsequent to long-time survival from early eye loss

Genome Instability and Transcription Elongation Impairment in Human Cells Depleted of THO/TREX

THO/TREX connects transcription with genome integrity in yeast, but a role of mammalian THO in these processes is uncertain, which suggests a differential implication of mRNP biogenesis factors in genome integrity in yeast and humans. We show that human THO depletion impairs transcription elongation and mRNA export and increases instability associated with DNA breaks, leading to hyper-recombination and γH2AX and 53BP1 foci accumulation. This is accompanied by replication alteration as determined by DNA combing. Genome instability is R-loop–dependent, as deduced from the ability of the AID enzyme to increase DNA damage and of RNaseH to reduce it, or from the enhancement of R-loop–dependent class-switching caused by THOC1-depletion in CH12 murine cells. Therefore, mammalian THO prevents R-loop formation and has a role in genome dynamics and function consistent with an evolutionary conservation of the functional connection between these mRNP biogenesis factors and genome integrity that had not been anticipated

The SR Protein B52/SRp55 Is Required for DNA Topoisomerase I Recruitment to Chromatin, mRNA Release and Transcription Shutdown

DNA- and RNA-processing pathways are integrated and interconnected in the eukaryotic nucleus to allow efficient gene expression and to maintain genomic stability. The recruitment of DNA Topoisomerase I (Topo I), an enzyme controlling DNA supercoiling and acting as a specific kinase for the SR-protein family of splicing factors, to highly transcribed loci represents a mechanism by which transcription and processing can be coordinated and genomic instability avoided. Here we show that Drosophila Topo I associates with and phosphorylates the SR protein B52. Surprisingly, expression of a high-affinity binding site for B52 in transgenic flies restricted localization, not only of B52, but also of Topo I to this single transcription site, whereas B52 RNAi knockdown induced mis-localization of Topo I in the nucleolus. Impaired delivery of Topo I to a heat shock gene caused retention of the mRNA at its site of transcription and delayed gene deactivation after heat shock. Our data show that B52 delivers Topo I to RNA polymerase II-active chromatin loci and provide the first evidence that DNA topology and mRNA release can be coordinated to control gene expression