DMC1 attenuates RAD51-mediated recombination in Arabidopsis.

Ensuring balanced distribution of chromosomes in gametes, meiotic recombination is essential for fertility in most sexually reproducing organisms. The repair of the programmed DNA double strand breaks that initiate meiotic recombination requires two DNA strand-exchange proteins, RAD51 and DMC1, to search for and invade an intact DNA molecule on the homologous chromosome. DMC1 is meiosis-specific, while RAD51 is essential for both mitotic and meiotic homologous recombination. DMC1 is the main catalytically active strand-exchange protein during meiosis, while this activity of RAD51 is downregulated. RAD51 is however an essential cofactor in meiosis, supporting the function of DMC1. This work presents a study of the mechanism(s) involved in this and our results point to DMC1 being, at least, a major actor in the meiotic suppression of the RAD51 strand-exchange activity in plants. Ectopic expression of DMC1 in somatic cells renders plants hypersensitive to DNA damage and specifically impairs RAD51-dependent homologous recombination. DNA damage-induced RAD51 focus formation in somatic cells is not however suppressed by ectopic expression of DMC1. Interestingly, DMC1 also forms damage-induced foci in these cells and we further show that the ability of DMC1 to prevent RAD51-mediated recombination is associated with local assembly of DMC1 at DNA breaks. In support of our hypothesis, expression of a dominant negative DMC1 protein in meiosis impairs RAD51-mediated DSB repair. We propose that DMC1 acts to prevent RAD51-mediated recombination in Arabidopsis and that this down-regulation requires local assembly of DMC1 nucleofilaments.

RAD54 is essential for RAD51-mediated repair of meiotic DSB in Arabidopsis.

An essential component of the homologous recombination machinery in eukaryotes, the RAD54 protein is a member of the SWI2/SNF2 family of helicases with dsDNA-dependent ATPase, DNA translocase, DNA supercoiling and chromatin remodelling activities. It is a motor protein that translocates along dsDNA and performs multiple functions in homologous recombination. In particular, RAD54 is an essential cofactor for regulating RAD51 activity. It stabilizes the RAD51 nucleofilament, remodels nucleosomes, and stimulates the homology search and strand invasion activities of RAD51. Accordingly, deletion of RAD54 has dramatic consequences on DNA damage repair in mitotic cells. In contrast, its role in meiotic recombination is less clear. RAD54 is essential for meiotic recombination in Drosophila and C. elegans, but plays minor roles in yeast and mammals. We present here characterization of the roles of RAD54 in meiotic recombination in the model plant Arabidopsis thaliana. Absence of RAD54 has no detectable effect on meiotic recombination in otherwise wild-type plants but RAD54 becomes essential for meiotic DSB repair in absence of DMC1. In Arabidopsis, dmc1 mutants have an achiasmate meiosis, in which RAD51 repairs meiotic DSBs. Lack of RAD54 leads to meiotic chromosomal fragmentation in absence of DMC1. The action of RAD54 in meiotic RAD51 activity is thus mainly downstream of the role of RAD51 in supporting the activity of DMC1. Equivalent analyses show no effect on meiosis of combining dmc1 with the mutants of the RAD51-mediators RAD51B, RAD51D and XRCC2. RAD54 is thus required for repair of meiotic DSBs by RAD51 and the absence of meiotic phenotype in rad54 plants is a consequence of RAD51 playing a RAD54-independent supporting role to DMC1 in meiotic recombination.

LSD1-LIKE1-Mediated H3K4me2 Demethylation Is Required for Homologous Recombination Repair.

Homologous recombination is a key process for maintaining genome integrity and diversity. In eukaryotes, the nucleosome structure of chromatin inhibits the progression of homologous recombination. The DNA repair and recombination protein RAD54 alters the chromatin structure via nucleosome sliding to enable homology searches. For homologous recombination to progress, appropriate recruitment and dissociation of RAD54 is required at the site of homologous recombination; however, little is known about the mechanism regulating RAD54 dynamics in chromatin. Here, we reveal that the histone demethylase LYSINE-SPECIFIC DEMETHYLASE1-LIKE 1 (LDL1) regulates the dissociation of RAD54 at damaged sites during homologous recombination repair in the somatic cells of Arabidopsis (Arabidopsis thaliana). Depletion of LDL1 leads to an overaccumulation of RAD54 at damaged sites with DNA double-strand breaks. Moreover, RAD54 accumulates at damaged sites by recognizing histone H3 Lys 4 di-methylation (H3K4me2); the frequency of the interaction between RAD54 and H3K4me2 increased in the ldl1 mutant with DNA double-strand breaks. We propose that LDL1 removes RAD54 at damaged sites by demethylating H3K4me2 during homologous recombination repair and thereby maintains genome stability in Arabidopsis.

RAD51 and RTEL1 compensate telomere loss in the absence of telomerase.

Replicative erosion of telomeres is naturally compensated by telomerase and studies in yeast and vertebrates show that homologous recombination can compensate for the absence of telomerase. We show that RAD51 protein, which catalyzes the key strand-invasion step of homologous recombination, is localized at Arabidopsis telomeres in absence of telomerase. Blocking the strand-transfer activity of the RAD51 in telomerase mutant plants results in a strikingly earlier onset of developmental defects, accompanied by increased numbers of end-to-end chromosome fusions. Imposing replication stress through knockout of RNaseH2 increases numbers of chromosome fusions and reduces the survival of these plants deficient for telomerase and homologous recombination. This finding suggests that RAD51-dependent homologous recombination acts as an essential backup to the telomerase for compensation of replicative telomere loss to ensure genome stability. Furthermore, we show that this positive role of RAD51 in telomere stability is dependent on the RTEL1 helicase. We propose that a RAD51 dependent break-induced replication process is activated in cells lacking telomerase activity, with RTEL1 responsible for D-loop dissolution after telomere replication.

The Structure-Specific Endonucleases MUS81 and SEND1 Are Essential for Telomere Stability in Arabidopsis.

Structure-specific endonucleases act to repair potentially toxic structures produced by recombination and DNA replication, ensuring proper segregation of the genetic material to daughter cells during mitosis and meiosis. Arabidopsis thaliana has two putative homologs of the resolvase (structure-specific endonuclease): GEN1/Yen1. Knockout of resolvase genes GEN1 and SEND1, individually or together, has no detectable effect on growth, fertility, or sensitivity to DNA damage. However, combined absence of the endonucleases MUS81 and SEND1 results in severe developmental defects, spontaneous cell death, and genome instability. A similar effect is not seen in mus81 gen1 plants, which develop normally and are fertile. Absence of RAD51 does not rescue mus81 send1, pointing to roles of these proteins in DNA replication rather than DNA break repair. The enrichment of S-phase histone γ-H2AX foci and a striking loss of telomeric DNA in mus81 send1 further support this interpretation. SEND1 has at most a minor role in resolution of the Holliday junction but acts as an essential backup to MUS81 for resolution of toxic replication structures to ensure genome stability and to maintain telomere integrity.

Homology-dependent repair is involved in 45S rDNA loss in plant CAF-1 mutants.

Arabidopsis thaliana mutants in FAS1 and FAS2 subunits of chromatin assembly factor 1 (CAF1) show progressive loss of 45S rDNA copies and telomeres. We hypothesized that homology-dependent DNA damage repair (HDR) may contribute to the loss of these repeats in fas mutants. To test this, we generated double mutants by crossing fas mutants with knock-out mutants in RAD51B, one of the Rad51 paralogs of A. thaliana. Our results show that the absence of RAD51B decreases the rate of rDNA loss, confirming the implication of RAD51B-dependent recombination in rDNA loss in the CAF1 mutants. Interestingly, this effect is not observed for telomeric repeat loss, which thus differs from that acting in rDNA loss. Involvement of DNA damage repair in rDNA dynamics in fas mutants is further supported by accumulation of double-stranded breaks (measured as γ-H2AX foci) in 45S rDNA. Occurrence of the foci is not specific for S-phase, and is ATM-independent. While the foci in fas mutants occur both in the transcribed (intranucleolar) and non-transcribed (nucleoplasmic) fraction of rDNA, double fas rad51b mutants show a specific increase in the number of the intranucleolar foci. These results suggest that the repair of double-stranded breaks present in the transcribed rDNA region is RAD51B dependent and that this contributes to rDNA repeat loss in fas mutants, presumably via the single-stranded annealing recombination pathway. Our results also highlight the importance of proper chromatin assembly in the maintenance of genome stability.

Recombination-independent mechanisms and pairing of homologous chromosomes during meiosis in plants.

Meiosis is the specialized eukaryotic cell division that permits the halving of ploidy necessary for gametogenesis in sexually reproducing organisms. This involves a single round of DNA replication followed by two successive divisions. To ensure balanced segregation, homologous chromosome pairs must migrate to opposite poles at the first meiotic division and this means that they must recognize and pair with each other beforehand. Although understanding of the mechanisms by which meiotic chromosomes find and pair with their homologs has greatly advanced, it remains far from being fully understood. With some notable exceptions such as male Drosophila, the recognition and physical linkage of homologs at the first meiotic division involves homologous recombination. However, in addition to this, it is clear that many organisms, including plants, have also evolved a series of recombination-independent mechanisms to facilitate homolog recognition and pairing. These implicate chromosome structure and dynamics, telomeres, centromeres, and, most recently, small RNAs. With a particular focus on plants, we present here an overview of understanding of these early, recombination-independent events that act in the pairing of homologous chromosomes during the first meiotic division.

Multiple host-cell recombination pathways act in Agrobacterium-mediated transformation of plant cells.

Using floral-dip, tumorigenesis and root callus transformation assays of both germline and somatic cells, we present here results implicating the four major non-homologous and homologous recombination pathways in Agrobacterium-mediated transformation of Arabidopsis thaliana. All four single mutant lines showed similar mild reductions in transformability, but knocking out three of four pathways severely compromised Agrobacterium-mediated transformation. Although integration of T-DNA into the plant genome is severely compromised in the absence of known DNA double-strand break repair pathways, it does still occur, suggesting the existence of other pathways involved in T-DNA integration. Our results highlight the functional redundancy of the four major plant recombination pathways in transformation, and provide an explanation for the lack of strong effects observed in previous studies on the roles of plant recombination functions in transformation.

Roles of XRCC2, RAD51B and RAD51D in RAD51-independent SSA recombination.

The repair of DNA double-strand breaks by recombination is key to the maintenance of genome integrity in all living organisms. Recombination can however generate mutations and chromosomal rearrangements, making the regulation and the choice of specific pathways of great importance. In addition to end-joining through non-homologous recombination pathways, DNA breaks are repaired by two homology-dependent pathways that can be distinguished by their dependence or not on strand invasion catalysed by the RAD51 recombinase. Working with the plant Arabidopsis thaliana, we present here an unexpected role in recombination for the Arabidopsis RAD51 paralogues XRCC2, RAD51B and RAD51D in the RAD51-independent single-strand annealing pathway. The roles of these proteins are seen in spontaneous and in DSB-induced recombination at a tandem direct repeat recombination tester locus, both of which are unaffected by the absence of RAD51. Individual roles of these proteins are suggested by the strikingly different severities of the phenotypes of the individual mutants, with the xrcc2 mutant being the most affected, and this is confirmed by epistasis analyses using multiple knockouts. Notwithstanding their clearly established importance for RAD51-dependent homologous recombination, XRCC2, RAD51B and RAD51D thus also participate in Single-Strand Annealing recombination.

Meiotic recombination in Arabidopsis is catalysed by DMC1, with RAD51 playing a supporting role.

Recombination establishes the chiasmata that physically link pairs of homologous chromosomes in meiosis, ensuring their balanced segregation at the first meiotic division and generating genetic variation. The visible manifestation of genetic crossing-overs, chiasmata are the result of an intricate and tightly regulated process involving induction of DNA double-strand breaks and their repair through invasion of a homologous template DNA duplex, catalysed by RAD51 and DMC1 in most eukaryotes. We describe here a RAD51-GFP fusion protein that retains the ability to assemble at DNA breaks but has lost its DNA break repair capacity. This protein fully complements the meiotic chromosomal fragmentation and sterility of Arabidopsis rad51, but not rad51 dmc1 mutants. Even though DMC1 is the only active meiotic strand transfer protein in the absence of RAD51 catalytic activity, no effect on genetic map distance was observed in complemented rad51 plants. The presence of inactive RAD51 nucleofilaments is thus able to fully support meiotic DSB repair and normal levels of crossing-over by DMC1. Our data demonstrate that RAD51 plays a supporting role for DMC1 in meiotic recombination in the flowering plant, Arabidopsis.

Signaling of double strand breaks and deprotected telomeres in Arabidopsis.

Failure to repair DNA double strand breaks (DSB) can lead to chromosomal rearrangements and eventually to cancer or cell death. Radiation and environmental pollutants induce DSB and this is of particular relevance to plants due to their sessile life style. DSB also occur naturally in cells during DNA replication and programmed induction of DSB initiates the meiotic recombination essential for gametogenesis in most eukaryotes. The linear nature of most eukaryotic chromosomes means that each chromosome has two "broken" ends. Chromosome ends, or telomeres, are protected by nucleoprotein caps which avoid their recognition as DSB by the cellular DNA repair machinery. Deprotected telomeres are recognized as DSB and become substrates for recombination leading to chromosome fusions, the "bridge-breakage-fusion" cycle, genome rearrangements and cell death. The importance of repair of DSB and the severity of the consequences of their misrepair have led to the presence of multiple, robust mechanisms for their detection and repair. After a brief overview of DSB repair pathways to set the context, we present here an update of current understanding of the detection and signaling of DSB in the plant, Arabidopsis thaliana.

Effects of XRCC2 and RAD51B mutations on somatic and meiotic recombination in Arabidopsis thaliana.

Homologous recombination is key to the maintenance of genome integrity and the creation of genetic diversity. At the mechanistic level, recombination involves the invasion of a homologous DNA template by broken DNA ends, repair of the break and exchange of genetic information between the two DNA molecules. Invasion of the template in eukaryotic cells is catalysed by the RAD51 and DMC1 recombinases, assisted by a number of accessory proteins, including the RAD51 paralogues. Eukaryotic genomes encode a variable number of RAD51 paralogues, ranging from two in yeast to five in animals and plants. The RAD51 paralogues form at least two distinct protein complexes, believed to play roles in the assembly and stabilization of the RAD51-DNA nucleofilament. Somatic recombination assays and immunocytology confirm that the three 'non-meiotic' paralogues of Arabidopsis, RAD51B, RAD51D and XRCC2, are involved in somatic homologous recombination, and that they are not required for the formation of radioinduced RAD51 foci. Given the presence of all five proteins in meiotic cells, the apparent absence of a meiotic role for RAD51B, RAD51D and XRCC2 is surprising, and perhaps simply the result of a more subtle meiotic phenotype in the mutants. Analysis of meiotic recombination confirms this, showing that the absence of XRCC2, and to a lesser extent RAD51B, but not RAD51D, increases rates of meiotic crossing over. The roles of RAD51B and XRCC2 in recombination are thus not limited to mitotic cells.

Gene targeting in maize by somatic ectopic recombination.

Low transformation efficiency and high background of non-targeted events are major constraints to gene targeting in plants. We demonstrate here applicability in maize of a system that reduces the constraint from transformation efficiency. The system requires regenerable transformants in which all of the following elements are stably integrated in the genome: (i) donor DNA with the gene of interest adjacent to sequence for repair of a defective selectable marker, (ii) sequence encoding a rare-cutting endonuclease such as I-SceI, (iii) a target locus (TL) comprising the defective selectable marker and I-SceI cleavage site. Typically, this requires additional markers for the integration of the donor and target sequences, which may be assembled through cross-pollination of separate transformants. Inducible expression of I-SceI then cleaves the TL and facilitates homologous recombination, which is assayed by selection for the repaired marker. We used bar and gfp markers to identify assembled transformants, a dexamethasone-inducible I-SceI::GR protein, and selection for recombination events that restored an intact nptII. Applying this strategy to callus permitted the selection of recombination into the TL at a frequency of 0.085% per extracted immature embryo (29% of recombinants). Our results also indicate that excision of the donor locus (DL) through the use of flanking I-SceI cleavage sites may be unnecessary, and a source of unwanted repair events at the DL. The system allows production, from each assembled transformant, of many cells that subsequently can be treated to induce gene targeting. This may facilitate gene targeting in plant species for which transformation efficiencies are otherwise limiting.

Xrcc1-dependent and Ku-dependent DNA double-strand break repair kinetics in Arabidopsis plants.

Double-strand breakage (DSB) of DNA involves loss of information on the two strands of the DNA fibre and thus cannot be repaired by simple copying of the complementary strand which is possible with single-strand DNA damage. Homologous recombination (HR) can precisely repair DSB using another copy of the genome as template and non-homologous recombination (NHR) permits repair of DSB with little or no dependence on DNA sequence homology. In addition to the well-characterised Ku-dependent non-homologous end-joining (NHEJ) pathway, much recent attention has been focused on Ku-independent NHR. The complex interrelationships and regulation of NHR pathways remain poorly understood, even more so in the case of plants, and we present here an analysis of Ku-dependent and Ku-independent repair of DSB in Arabidopsis thaliana. We have characterised an Arabidopsis xrcc1 mutant and developed quantitative analysis of the kinetics of appearance and loss of γ-H2AX foci as a tool to measure DSB repair in dividing root tip cells of γ-irradiated plants in vivo. This approach has permitted determination of DSB repair kinetics in planta following a short pulse of γ-irradiation, establishing the existence of a Ku-independent, Xrcc1-dependent DSB repair pathway. Furthermore, our data show a role for Ku80 during the first minutes post-irradiation and that Xrcc1 also plays such a role, but only in the absence of Ku. The importance of Xrcc1 is, however, clearly visible at later times in the presence of Ku, showing that alternative end-joining plays an important role in DSB repair even in the presence of active NHEJ.

Calidad en los servicios de salud desde los marcos de sentido de diferentes actores sociales en Colombia y Brasil / Quality of health-care according to social actors' frameworks of meaning in Colombia and Brazil

Objetivo Analizar los marcos de sentido en la definición de la calidad de un servicio de salud de los diversos actores sociales en Colombia y Brasil. Método Estudio cualitativo, descriptivo-interpretativo, mediante grupos focales y entrevistas individuales en dos municipios de Colombia y Brasil. Muestra teórica de agentes sociales, buscando variedad del discurso: a. Usuarios y líderes; b. Personal de salud y; c. Formuladores de políticas. Análisis de contenido, con generación mixta de categorías y segmentación de los datos por país, informantes y temas. Resultados Los marcos de sentido desde los cuales construyen la calidad de la atención, usuarios y personal de salud en ambos países, mostraron convergencias en torno a tres grandes ejes: adecuación de la estructura, nivel técnico y humanización de la atención. Presentaron, no obstante, matices diferenciadores: los usuarios de ambos países profundizan en aspectos estructurales y organizativos como disponibilidad y accesibilidad de recursos, y en aspectos técnicos, como resolutividad y calidad técnica. El personal de salud de Colombia y Brasil mostró similitudes, pero mientras los primeros destacaban más una administración ágil y tiempo de consulta mayor; los segundos, más disposición de personal especializado, materiales e insumos suficientes. Por su parte, el marco de sentido de los formuladores emergió del conjunto de normas legales. Conclusiones Los matices aportados por los distintos marcos de sentido de calidad de los actores sociales, indican la necesidad de tenerlos en cuenta en su totalidad, ya que apuntan a diferentes debilidades del sistema. Además, muestran que los usuarios profundizan más en aspectos técnicos del servicio de lo considerado habitualmente.

Objective To analyse social actors' frameworks of meaning regarding the definition of health-care quality in Colombia and Brazil. Method This was a descriptive, interpretative, qualitative study which used focus-groups and individual indepth interviews in two municipalities in Colombia and Brazil. The following social actors were theoretical sampled to represent the variety of views: users and leaders, health-care personnel and policy-makers. Content was analysed with mixed generation of categories and segmentation by country, actors and themes. Results The frameworks of meaning regarding health-care quality for users and health personnel in both countries revealed coincidences concerning three main topics: structural suitability, technical level and humanisation of care. However, they had differentiated meanings; users from both countries highlighted structural and organisational aspects, together with technical aspects such as resolution level and quality of care. Colombian and Brazilian health-care personnel shared some views but whilst the former highlighted non-bureaucratic and consultation time, the latter singled out the availability of specialised personnel, materials and equipment. Policy-makers' framework of meanings emerge from the legal framework. Conclusions Features provided by the social actors' frameworks of meaning indicated the need to take them all into consideration as they all pointed out different system weaknesses. They also showed that users valued technical quality more than is generally considered.

[Quality of health-care according to social actors' frameworks of meaning in Colombia and Brazil]. / Calidad en los servicios de salud desde los marcos de sentido de diferentes actores sociales en Colombia y Brasil.

OBJECTIVE: To analyse social actors' frameworks of meaning regarding the definition of health-care quality in Colombia and Brazil. METHOD: This was a descriptive, interpretative, qualitative study which used focus-groups and individual indepth interviews in two municipalities in Colombia and Brazil. The following social actors were theoretical sampled to represent the variety of views: users and leaders, health-care personnel and policy-makers. Content was analysed with mixed generation of categories and segmentation by country, actors and themes. RESULTS: The frameworks of meaning regarding health-care quality for users and health personnel in both countries revealed coincidences concerning three main topics: structural suitability, technical level and humanisation of care. However, they had differentiated meanings; users from both countries highlighted structural and organisational aspects, together with technical aspects such as resolution level and quality of care. Colombian and Brazilian health-care personnel shared some views but whilst the former highlighted non-bureaucratic and consultation time, the latter singled out the availability of specialised personnel, materials and equipment. Policy-makers' framework of meanings emerge from the legal framework. CONCLUSIONS: Features provided by the social actors' frameworks of meaning indicated the need to take them all into consideration as they all pointed out different system weaknesses. They also showed that users valued technical quality more than is generally considered.

[Barriers and opportunities for social participation in health: the main social actors' perceptions]. / Barreras y oportunidades para la participación social en salud en Colombia: percepciones de los actores principales.

OBJECTIVE: Analysing barriers to and opportunities for user involvement as perceived by the social actors involved in implementing Colombian policy regarding social participation in health. METHODS: An exploratory qualitative study was carried out in the Colombian towns of Tuluá and Palmira between 2000 and 2001. There were 10 focus groups having 260 users and leaders. Semi-structured individual interviews were given to health personnel (36) and policy-makers (3). Narrative content, mixed categories and data segmentation by informants and topics were then analysed. RESULTS: Users and leaders considered their own lack of knowledge, apathy and fear of revenge as barriers for participation. However, there were institutional factors such as lack of institutional transparency, limited receptiveness and responsiveness regarding participation. These opinions were shared by policy-makers. Most health personnel identified users' knowledge and attitudes as barriers for participation; few mentioned any institutional barriers such as the behaviour of personnel, institutional opacity and the lack of resources for fostering work in the community. Opportunities for participation were described in terms of suitable and possible scenarios. Users perceived their great ability to achieve change through their direct participation appeared to them as presenting an important opportunity. CONCLUSIONS: Users' and leaders' perceptions of the current barriers and opportunities seemed to show that they are critical of their own reality and constitute important potential actors for becoming key interlocutors with institutions and the state. A similar attitude would be necessary on the part of institutional actors to build a real and permanent participatory culture.

Conocimientos, opiniones y experiencias con la aplicación de las políticas de participación en salud en Colombia / Knowledge, opinions and experience from applying health participation policy in Colombia

Objetivo: Analizar el conocimiento y opiniones sobre las políticas de participación en salud y la experiencia con los mecanismos de participación de usuarios, líderes comunitarios y personal de salud en Colombia. Método Entre 1999 y 2001 se realizó en los municipios Tulúa y Palmira, Colombia, una investigación exploratoria y descriptiva que combinó métodos cuantitativos, encuesta a una muestra de 1 497 usuarios, con métodos cualitativos, a través de grupos focales a 210 usuarios y 40 líderes y 36 entrevistas individuales semi-estructuradas a personal de salud. Se realizó un análisis descriptivo de los resultados de la encuesta, mediante el SPSS, y un análisis narrativo de contenido de los datos cualitativos, mediante el Ethnograph. Resultados La encuesta a los usuarios mostró un gran desconocimiento de la normatividad y los mecanismos de participación formal y un uso limitado de los mismos. Desconocimiento y cierto escepticismo sobre su eficacia se reflejó en el estudio cualitativo con usuarios, líderes y personal de salud. El personal del sector público mostraba un concepto más elaborado y refería una mayor implementación de mecanismos. Entre las dificultades para la implementación destacan carencia de recursos y de cultura participativa. Conclusiones Los resultados muestran un conocimiento y uso escaso de los mecanismos de participación social en salud, con predominio de los basados en el mercado. Se requiere importante una intervención en información y formación de la población y personal de salud para promover una participación real para el control social del sistema de salud.

Objective: Analysing knowledge and opinions regarding policies related to social participation in health and how user, community leader and health personnel participation mechanisms are used in Colombia. Methods An exploratory and descriptive study was carried out between 1999 and 2001 in the towns of Tuluá and Palmira in Colombia using a combination of research methods. A sample of 1,497 health care users were formally surveyed, a focus-group-based qualitative study was made of 210 users and 40 community leaders and 36 semi-structured individual interviews were conducted with health personnel. SPSS was used for a descriptive analysis of survey data and Ethnograph for narrative content analysis of qualitative data. Results The user survey results revealed a lack of knowledge regarding norms and mechanisms for social participation in health, as well as limited use. Limited knowledge and scepticism regarding its effectiveness was also reflected in the users, leaders and health personnel qualitative study results. Public sector personnel, however, displayed better knowledge and referred to greater implementation of participation mechanisms. Lack of both resources and a culture of participation were amongst the difficulties faced in implementing it. Conclusions The results indicated scarce knowledge and little use of social participation in health mechanisms (market-based ones predominating). Much greater investment in information and training the population and health system personnel is required as a first step towards promoting real social participation for social control of the health system.

Barreras y oportunidades para la participación social en salud en Colombia: percepciones de los actores principales / Barriers and opportunities for social participation in health: the main social actors' perceptions

OBJETIVO: Analizar los obstáculos y oportunidades para la participación percibidos por los actores implicados en la política de participación social en salud en Colombia. MÉTODOS: Estudio cualitativo exploratorio, en los municipios de Tulua y Palmira, entre 2000 y 2001, a través de grupos focales a usuarios y líderes (260); entrevistas individuales semi-estructuradas a personal de salud (36) y formuladores de políticas (3). Se realizó un análisis de contenido, con generación mixta de categorías y segmentación de los datos por informantes y temas. RESULTADOS: Usuarios y líderes identificaron como obstáculos a participar: su falta de conocimiento, apatía y temor a represalias; también, factores institucionales como la falta de claridad, limitada apertura y respuesta institucional en los procesos participativos; opinión que compartían los formuladores de políticas. La mayoría del personal de salud atribuía las barreras a los conocimientos y actitudes de los usuarios; sólo algunos mencionaban barreras institucionales, como el comportamiento del personal, la limitada capacidad o recursos institucionales para impulsar el trabajo comunitario. Las oportunidades para participar eran descritas como escenarios deseados y posibles. La alta capacidad percibida por los usuarios para conseguir cambios a través de su participación surge como importante oportunidad. CONCLUSIONES: Las percepciones de usuarios y líderes sobre las barreras y oportunidades parecen indicar que son actores críticos de su realidad y se constituyen en importante potencial para configurarse en interlocutores clave con las instituciones y el Estado. Una actitud semejante por parte de instituciones sería necesaria para construir una auténtica y duradera cultura participativa.

Recent advances in understanding of the DNA double-strand break repair machinery of plants.

Living cells suffer numerous and varied alterations of their genetic material. Of these, the DNA double-strand break (DSB) is both particularly threatening and common. Double-strand breaks arise from exposure to DNA damaging agents, but also from cell metabolism-in a fortuitous manner during DNA replication or repair of other kinds of lesions and in a programmed manner, for example during meiosis or V(D)J gene rearrangement. Cells possess several overlapping repair pathways to deal with these breaks, generally designated as genetic recombination. Genetic and biochemical studies have provided considerable amounts of data about the proteins involved in recombination processes and their functions within these processes. Although they have long played a key role in building understanding of genetics, relatively little is known at the molecular level of the genetic recombination processes in plants. The use of reverse genetic approaches and the public availability of sequence tagged mutants in Arabidopsis thaliana have led to increasingly rapid progress in this field over recent years. The rapid progress of studies of recombination in plants is obviously not limited to the DSB repair machinery as such and we ask readers to understand that in order to maintain the focus and to rest within a reasonable length, we present only limited discussion of the exciting advances in the of plant meiosis field, which require a full review in their own right . We thus present here an update on recent advances in understanding of the DSB repair machinery of plants, focussing on Arabidopsis and making a particular effort to place these in the context of more general of understanding of these processes.