Timely lagging strand maturation relies on Ubp10 deubiquitylase-mediated PCNA dissociation from replicating chromatin.

Synthesis and maturation of Okazaki Fragments is an incessant and highly efficient metabolic process completing the synthesis of the lagging strands at replication forks during S phase. Accurate Okazaki fragment maturation (OFM) is crucial to maintain genome integrity and, therefore, cell survival in all living organisms. In eukaryotes, OFM involves the consecutive action of DNA polymerase Pol ∂, 5' Flap endonuclease Fen1 and DNA ligase I, and constitutes the best example of a sequential process coordinated by the sliding clamp PCNA. For OFM to occur efficiently, cooperation of these enzymes with PCNA must be highly regulated. Here, we present evidence of a role for the K164-PCNA-deubiquitylase Ubp10 in the maturation of Okazaki fragments in the budding yeast Saccharomyces cerevisiae. We show that Ubp10 associates with lagging-strand DNA synthesis machineries on replicating chromatin to ensure timely ligation of Okazaki fragments by promoting PCNA dissociation from chromatin requiring lysine 164 deubiquitylation.

Neu1 deficiency and fibrotic lymph node microenvironment lead to imbalance in M1/M2 macrophage polarization.

Macrophages play a pivotal role in tissue homeostasis, pathogen defense, and inflammation resolution. M1 and M2 macrophage phenotypes represent two faces in a spectrum of responses to microenvironmental changes, crucial in both physiological and pathological conditions. Neuraminidase 1 (Neu1), a lysosomal and cell surface sialidase responsible for removing terminal sialic acid residues from glycoconjugates, modulates several macrophage functions, including phagocytosis and Toll-like receptor (TLR) signaling. Current evidence suggests that Neu1 expression influences M1/M2 macrophage phenotype alterations in the context of cardiovascular diseases, indicating a potential role for Neu1 in macrophage polarization. For this reason, we investigated the impact of Neu1 deficiency on macrophage polarization in vitro and in vivo. Using bone marrow-derived macrophages (BMDMs) and peritoneal macrophages from Neu1 knockout (Neu1-/- ) mice and wild-type (WT) littermate controls, we demonstrated that Neu1-deficient macrophages exhibit an aberrant M2-like phenotype, characterized by elevated macrophage mannose receptor 1 (MMR/CD206) expression and reduced responsiveness to M1 stimuli. This M2-like phenotype was also observed in vivo in peritoneal and splenic macrophages. However, lymph node (LN) macrophages from Neu1-/- mice exhibited phenotypic alterations with reduced CD206 expression. Further analysis revealed that peripheral LNs from Neu1-/- mice were highly fibrotic, with overexpression of transforming growth factor-beta 1 (TGF-ß1) and hyperactivated TGF-ß signaling in LN macrophages. Consistently, TGF-ß1 was found to alter M1/M2 macrophage polarization in vitro. Our findings showed that Neu1 deficiency prompts macrophages towards an M2 phenotype and that microenvironmental changes, particularly increased TGF-ß1 in fibrotic tissues such as peripheral LNs in Neu1-/- mice, further influence M1/M2 macrophage polarization, highlighting its sensitivity to the local microenvironment. Therapeutic interventions targeting Neu1 or TGF-ß signaling pathways may offer the potential to regulate macrophage behavior across different diseases.

Yerba Mate (Ilex paraguariensis) Reduces Colitis Severity by Promoting Anti-Inflammatory Macrophage Polarization.

Yerba Mate (YM) (Ilex paraguariensis) is a natural herbal supplement with a well-described anti-inflammatory capacity and beneficial effects in different inflammatory contexts such as insulin resistance or obesity. However, whether YM could improve other inflammatory conditions such as colitis or the immune cell population that can be modulated by this plant remains elusive. Here, by using 61 male and female C57BL/6/J wild-type (WT) mice and the dextran sodium sulfate (DSS)-induced acute colitis model, we evaluated the effect of YM on colitis symptoms and macrophage polarization. Our results showed that the oral administration of YM reduces colitis symptoms and improves animal survival. Increasing infiltration of anti-inflammatory M2 macrophage was observed in the colon of the mice treated with YM. Accordingly, YM promoted M2 macrophage differentiation in vivo. However, the direct administration of YM to bone marrow-derived macrophages did not increase anti-inflammatory polarization, suggesting that YM, through an indirect mechanism, is able to skew the M1/M2 ratio. Moreover, YM consumption reduced the Eubacterium rectale/Clostridium coccoides and Enterobacteriaceae groups and increased the Lactobacillus/Lactococcus group in the gut microbiota. In summary, we show that YM promotes an immunosuppressive environment by enhancing anti-inflammatory M2 macrophage differentiation, reducing colitis symptoms, and suggesting that YM consumption may be a good cost-effective treatment for ulcerative colitis.

Fission yeast Cdc14-like phosphatase Flp1/Clp1 modulates the transcriptional response to oxidative stress.

Reactive oxygen species (ROS) are an important source of cellular damage. When ROS intracellular levels increase, oxidative stress takes place affecting DNA stability and metabolic functions. To prevent these effects, stress-activated protein kinases (SAPKs) delay cell cycle progression and induce a transcriptional response that activates antioxidant mechanisms ensuring cell adaptation and survival. Fission yeast Cdc14-like phosphatase Flp1 (also known as Clp1) has a well-established role in cell cycle regulation. Moreover, Flp1 contributes to checkpoint activation during replication stress. Here, we show that Flp1 has a role in fine-tuning the cellular oxidative stress response. Phosphorylation-dependent nucleolar release of Flp1 in response to oxidative stress conditions plays a role in the cellular transcriptional response. Thus, Flp1 ablation increases the transcriptional response to oxidative stress, in both intensity and duration, upregulating both Atf1/Pcr1- and Pap1-dependent stress induced genes. Remarkably, we found that Flp1 interacts with the Atf1/Pcr1 complex with Pcr1 acting as a direct substrate. Our results provide evidence that Flp1 modulates the oxidative stress response by limiting the Atf1/Pcr1-mediated transcription.

Functional crosstalk between the cohesin loader and chromatin remodelers.

The cohesin complex participates in many structural and functional aspects of genome organization. Cohesin recruitment onto chromosomes requires nucleosome-free DNA and the Scc2-Scc4 cohesin loader complex that catalyzes topological cohesin loading. Additionally, the cohesin loader facilitates promoter nucleosome clearance in a yet unknown way, and it recognizes chromatin receptors such as the RSC chromatin remodeler. Here, we explore the cohesin loader-RSC interaction. Amongst multi-pronged contacts by Scc2 and Scc4, we find that Scc4 contacts a conserved patch on the RSC ATPase motor module. The cohesin loader directly stimulates in vitro nucleosome sliding by RSC, providing an explanation how it facilitates promoter nucleosome clearance. Furthermore, we observe cohesin loader interactions with a wide range of chromatin remodelers. Our results provide mechanistic insight into how the cohesin loader recognizes, as well as influences, the chromatin landscape, with implications for our understanding of human developmental disorders including Cornelia de Lange and Coffin-Siris syndromes.

Mediator recruits the cohesin loader Scc2 to RNA Pol II-transcribed genes and promotes sister chromatid cohesion.

The ring-like cohesin complex plays an essential role in chromosome segregation, organization, and double-strand break repair through its ability to bring two DNA double helices together. Scc2 (NIPBL in humans) together with Scc4 functions as the loader of cohesin onto chromosomes. Chromatin adapters such as the RSC complex facilitate the localization of the Scc2-Scc4 cohesin loader. Here, we identify a broad range of Scc2-chromatin protein interactions that are evolutionarily conserved and reveal a role for one complex, Mediator, in the recruitment of the cohesin loader. We identified budding yeast Med14, a subunit of the Mediator complex, as a high copy suppressor of poor growth in Scc2 mutant strains. Physical and genetic interactions between Scc2 and Mediator are functionally substantiated in direct recruitment and cohesion assays. Depletion of Med14 results in defective sister chromatid cohesion and the decreased binding of Scc2 at RNA Pol II-transcribed genes. Previous work has suggested that Mediator, Nipbl, and cohesin connect enhancers and promoters of active mammalian genes. Our studies suggest an evolutionarily conserved fundamental role for Mediator in the direct recruitment of Scc2 to RNA Pol II-transcribed genes.

Assessment of the operational characteristics of the National Comprehensive Cancer Network distress management tool, v. 2.2018, in patients seen at the Instituto Nacional de Cancerología, Bogotá / Evaluación de las características operativas de la versión 2.2018 del instrumento de evaluación del malestar emocional de la National Comprehensive Cancer Network en pacientes atendidos en el Instituto Nacional de Cancerología, Bogotá

Introduction: Cancer patients have significant levels of emotional distress. The National Comprehensive Cancer Network (NCCN) developed the distress management tool to quickly assess significant distress in oncological patients who require intervention. For its use in Colombia, we made its cross-cultural adaptation and validation. Objective: To determine the operative characteristics of the distress management tool, version 2.2018, in patients seen at the Instituto Nacional de Cancerología (INC) in Colombia. Materials and methods: Counting with the authorization from the NCCN, we translated, made the cross-cultural adaptation, and evaluated the operational characteristics of the tool. We included 343 cancer patients seen at the INC, who filled out the cross-culturally adapted instrument. A diagnostic test study was carried out with a semi-structured interview as a reference. Results: The patients had an average age of 49.7 years (SD=15) and the majority were women (67%). The instrument had an area under the ROC curve of 0.81 (95% CI: 0.77 -0.86); its optimal cut-off point was 3.5 approached to 4 when using integers on the scale; its sensitivity was 0.81 (95% CI: 0.76 - 0.85), and its specificity, 0.69 (95% CI: 0.64 - 0.74). The agreement percentage between the result of the interview and the instrument was 73% (kappa = 0.64; p< 0.001). Conclusions: The distress management tool allowed for the detection of moderate to severe distress requiring intervention and management. This instrument was adapted and validated in cancer patients in Colombia keeping the cutoff point at ≥ 4 as in the original version.

Introducción. Los pacientes con cáncer presentan niveles significativos de malestar emocional. La National Comprehensive Cancer Network (NCCN) desarrolló un instrumento (Distress Management) para evaluarlo de forma rápida en pacientes oncológicos. Para su utilización en Colombia, se hizo la adaptación transcultural y se validó. Objetivo. Determinar las características operativas del instrumento de malestar emocional, versión 2.2018, en pacientes atendidos en el Instituto Nacional de Cancerología. Materiales y métodos. Previa autorización de la NCCN, se procedió a la traducción, adaptación transcultural y evaluación de las características operativas del instrumento. Se incluyeron 343 pacientes con diagnóstico de cáncer atendidos en el Instituto Nacional de Cancerología, quienes diligenciaron el instrumento adaptado transculturalmente. Se efectuó un estudio de prueba diagnóstica como patrón de referencia mediante una entrevista semiestructurada. Resultados. Los pacientes tenían una edad promedio de 49,7 años (DE=15) y la mayoría (67 %) eran mujeres. El instrumento tuvo un área bajo la curva ROC de 0,81 (IC95% 0,77-0,86); el punto de corte óptimo fue de 3,5, el cual se aproximó a 4; la sensibilidad fue de 0,81 (IC95% 0,76-0,85) y la especificidad de 0,69 (IC95% 0,64-0,74). El porcentaje de acuerdo entre el resultado de la entrevista y el instrumento fue de 73 % (kappa=0,64; p<0,001). Conclusiones. El instrumento de malestar emocional permitió detectar el malestar emocional moderado a grave que requiere intervención y manejo. Este instrumento fue adaptado y validado en pacientes con cáncer en Colombia, conservándose el punto de corte en ≥4 como en la versión original.

Evaluación de las características operativas de la versión 2. 2018 del instrumento de evaluación del malestar emocional de la National Comprehensive Cancer Network en pacientes atendidos en el Instituto Nacional de Cancerología, Bogotá / Assessment of the operational characteristics of the National Comprehensive Cancer Network distress management tool, v. 2.2018, in patients seen at the Instituto Nacional de Cancerología, Bogotá

Resumen | Introducción. Los pacientes con cáncer presentan niveles significativos de malestar emocional. La National Comprehensive Cancer Network (NCCN) desarrolló un instrumento (Distress Management) para evaluarlo de forma rápida en pacientes oncológicos. Para su utilización en Colombia, se hizo la adaptación transcultural y se validó. Objetivo. Determinar las características operativas del instrumento de malestar emocional, versión 2.2018, en pacientes atendidos en el Instituto Nacional de Cancerología. Materiales y métodos. Previa autorización de la NCCN, se procedió a la traducción, adaptación transcultural y evaluación de las características operativas del instrumento. Se incluyeron 343 pacientes con diagnóstico de cáncer atendidos en el Instituto Nacional de Cancerología, quienes diligenciaron el instrumento adaptado transculturalmente. Se efectuó un estudio de prueba diagnóstica como patrón de referencia mediante una entrevista semiestructurada. Resultados. Los pacientes tenían una edad promedio de 49,7 años (DE=15) y la mayoría (67 %) eran mujeres. El instrumento tuvo un área bajo la curva ROC de 0,81 (IC95% 0,77-0,86); el punto de corte óptimo fue de 3,5, el cual se aproximó a 4; la sensibilidad fue de 0,81 (IC95% 0,76-0,85) y la especificidad de 0,69 (IC95% 0,64-0,74). El porcentaje de acuerdo entre el resultado de la entrevista y el instrumento fue de 73 % (kappa=0,64; p<0,001). Conclusiones. El instrumento de malestar emocional permitió detectar el malestar emocional moderado a grave que requiere intervención y manejo. Este instrumento fue adaptado y validado en pacientes con cáncer en Colombia, conservándose el punto de corte en ≥4 como en la versión original.

Abstract | Introduction: Cancer patients have significant levels of emotional distress. The National Comprehensive Cancer Network (NCCN) developed the distress management tool to quickly assess significant distress in oncological patients who require intervention. For its use in Colombia, we made its cross-cultural adaptation and validation. Objective: To determine the operative characteristics of the distress management tool, version 2.2018, in patients seen at the Instituto Nacional de Cancerología (INC) in Colombia. Materials and methods: Counting with the authorization from the NCCN, we translated, made the cross-cultural adaptation, and evaluated the operational characteristics of the tool. We included 343 cancer patients seen at the INC, who filled out the cross-culturally adapted instrument. A diagnostic test study was carried out with a semi-structured interview as a reference. Results: The patients had an average age of 49.7 years (SD=15) and the majority were women (67%). The instrument had an area under the ROC curve of 0.81 (95% CI: 0.77 - 0.86); its optimal cut-off point was 3.5 approached to 4 when using integers on the scale; its sensitivity was 0.81 (95% CI: 0.76 - 0.85), and its specificity, 0.69 (95% CI: 0.64 - 0.74). The agreement percentage between the result of the interview and the instrument was 73% (kappa = 0.64; p< 0.001). Conclusions: The distress management tool allowed for the detection of moderate to severe distress requiring intervention and management. This instrument was adapted and validated in cancer patients in Colombia keeping the cutoff point at ≥ 4 as in the original version.

Resultados funcionales a largo plazo de la cirugía abierta de liberación del túnel carpiano / Long-term functional outcomes of open carpal tunnel release surgery

Introducción: El síndrome del túnel carpiano es la neuropatía por atrapamiento más común que genera compresión del nervio mediano. La cirugía de liberación abierta del nervio mediano tiene un papel importante, especialmente, en pacientes que no responden al manejo conservador o con diagnóstico de síndrome del túnel carpiano con criterios de gravedad. El propósito de este estudio fue describir los resultados funcionales, la satisfacción y la fuerza objetiva a mediano (6-24 meses) y largo plazo (>24 meses) con la técnica abierta convencional en la población local. Materiales y métodos: Estudio observacional descriptivo con datos retrospectivos de resultados clínicos funcionales a mediano y largo plazo en pacientes sometidos a cirugía de liberación abierta del nervio mediano como tratamiento del síndrome del túnel carpiano. Se determinaron el nivel funcional según el BCTQ y la FSS, la fuerza de agarre con un dinamómetro electrónico y la satisfacción. Resultados: Se realizaron 100 procedimientos entre mayo de 2012 y septiembre de 2018, con un seguimiento posoperatorio >6 meses. La mayoría eran mujeres (83%) con una mediana de la edad de 59 años. El 97% obtuvo resultados buenos y excelentes a mediano plazo y el 90%, a largo plazo, con una mediana de fuerza de 17 kg (RIC 7,4) y una satisfacción de 90 (RIC 20) a mediano y largo plazo. Conclusiones: La cirugía abierta de liberación del nervio mediano en pacientes con síndrome del túnel carpiano logra resultados buenos y excelentes a mediano y largo plazo en cuanto a funcionalidad, fuerza y satisfacción. Nivel de Evidencia: IV

Introduction: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy that causes compression of the median nerve. Open median nerve release surgery plays an important role, especially in patients with failed conservative management or with a diagnosis of severe CTS. The purpose of the following study is to describe the functional outcomes, satisfaction, and objective strength in the medium (6 to 24 months) and long term (greater than 24 months) with the conventional open technique in the local population. Materials and methods: Descriptive observational study based on retrospective data of functional clinical outcomes in the medium and long term in patients undergoing open release surgery of the median nerve as a treatment for CTS. Functional level according to the BCTQ and FSS, grip strength with an electronic dynamometer, and satisfaction were determined. Results: 100 procedures were performed between May 2012 and September 2018, with a follow-up of more than 6 months. The majority were women (83%) with a total median age of 59 years showing good to excellent results in the 97% in the medium term and 90% in the long term, with a median strength of 17 kg (Interquartile range: 7.4) and satisfaction of 90 (Interquartile range: 20). Conclusions: Open surgery to release the median nerve in patients with CTS shows good to excellent functional outcomes, satisfaction, and strength in the medium and long term. Level of Evidence: IV

Conserved roles of chromatin remodellers in cohesin loading onto chromatin.

Cohesin is a conserved, ring-shaped protein complex that topologically entraps DNA. This ability makes this member of the structural maintenance of chromosomes (SMC) complex family a central hub of chromosome dynamics regulation. Besides its essential role in sister chromatid cohesion, cohesin shapes the interphase chromatin domain architecture and plays important roles in transcriptional regulation and DNA repair. Cohesin is loaded onto chromosomes at centromeres, at the promoters of highly expressed genes, as well as at DNA replication forks and sites of DNA damage. However, the features that determine these binding sites are still incompletely understood. We recently described a role of the budding yeast RSC chromatin remodeler in cohesin loading onto chromosomes. RSC has a dual function, both as a physical chromatin receptor of the Scc2/Scc4 cohesin loader complex, as well as by providing a nucleosome-free template for cohesin loading. Here, we show that the role of RSC in sister chromatid cohesion is conserved in fission yeast. We discuss what is known about the broader conservation of the contribution of chromatin remodelers to cohesin loading onto chromatin.

Adaptación transcultural al español de la escala Distress Management del NCCN versión 2. 2018 para su utilización en pacientes oncológicos en Colombia. / Transcultural adaptation to spanish of the Distress Management NCCN scale version 2.2018 for use in cancer patients in Colombia

Resumen Antecedentes: Los pacientes con diagnóstico de cáncer presentan niveles significativos de malestar emocional relacionados con la enfermedad oncológica. El termómetro de malestar emocional (Distress Management) es una herramienta diseñada por la National Comprehensive Cáncer Network (NCCN) para la medición del malestar emocional que requiere atención psicosocial en pacientes con cáncer como parte de los procesos usuales en la atención. Objetivo: Traducir y adaptar transculturalmente al español colombiano la versión en inglés de la escala Distress Management del NCCN versión 2.2018. Métodos: El proceso de traducción y adaptación transcultural se desarrolló siguiendo las recomendaciones metodológicas del grupo de calidad de vida EORTC (European Organization for Research and Treatment of Cáncer), realizando una traducción inicial, traducción inversa y una prueba piloto donde participaron 10 pacientes atendidos en el Instituto Nacional de Cancerología. Resultados: Se hizo la traducción de la escala Distress Management del NCCN versión 2.2018 encontrándose algunas discrepancias en la traducción directa e inversa, llegando a un consenso en cada etapa del proceso. En la prueba piloto, la escala fue respondida entre 5 a 9 minutos y se presentó dificultad en la comprensión de 6 ítems de la lista de problemas. Se decidió adicionar "cansancio" al ítem de fatiga, "psicoactivas" al ítem de uso de sustancias y realizar una explicación de las instrucciones previa a su diligenciamiento. Conclusión: Se realizó la adaptación transcultural de la escala Distress a una versión en español colombiano. Esta versión puede utilizarse para determinar sus propiedades psicométricas al aplicarse a pacientes con cáncer en Colombia.

Abstract Background: Patients diagnosed with cancer have significant levels of emotional distress related with oncological disease. The Distress Management is a tool designed by the NCCN (The National Comprehensive Cancer Network) for the measurement of emotional distress that requires psychosocial care in patients with cancer as part of the usual processes in care. Objective: Translate and cross-cultural comparison the English version of the Distress Management scale of NCCN version 2.2018 to Colombian Spanish. Methods: The transcultural translation and adaptation process was developed following the methodological recommendations of the EORTC quality of life group (European Organization for Research and Treatment of Cancer), performing an initial translation, inverse translation and a pilot test involving 10 patients treated at the National Institute of Cancerology Bogotá. Results: The translation of the thermometer was carried out, finding some discrepancies in the direct and inverse translation, reaching a consensus in each stage of the process. In the pilot test, the scale was answered between 5 to 9 minutes, there was difficulty in understanding 6 items in the list of problems. It was decided to add "tiredness" to the item of fatigue, "psychoactive" to the item of substance use and to make an explanation of the instructions prior to the patients reading and filling the instrument. Conclusion: The transcultural adaptation of the Distress Management of the NCCN version 2.2018 was made to a Colombian Spanish version. This version can be used to determine the psychometric properties when applied to cancer patients in Colombia.

A Role for Chromatin Remodeling in Cohesin Loading onto Chromosomes.

Cohesin is a conserved, ring-shaped protein complex that topologically embraces DNA. Its central role in genome organization includes functions in sister chromatid cohesion, DNA repair, and transcriptional regulation. Cohesin loading onto chromosomes requires the Scc2-Scc4 cohesin loader, whose presence on chromatin in budding yeast depends on the RSC chromatin remodeling complex. Here we reveal a dual role of RSC in cohesin loading. RSC acts as a chromatin receptor that recruits Scc2-Scc4 by a direct protein interaction independent of chromatin remodeling. In addition, chromatin remodeling is required to generate a nucleosome-free region that is the substrate for cohesin loading. An engineered cohesin loading module can be created by fusing the Scc2 C terminus to RSC or to other chromatin remodelers, but not to unrelated DNA binding proteins. These observations demonstrate the importance of nucleosome-free DNA for cohesin loading and provide insight into how cohesin accesses DNA during its varied chromosomal activities.

Cell-Cycle Regulation of Dynamic Chromosome Association of the Condensin Complex.

Eukaryotic cells inherit their genomes in the form of chromosomes, which are formed from the compaction of interphase chromatin by the condensin complex. Condensin is a member of the structural maintenance of chromosomes (SMC) family of ATPases, large ring-shaped protein assemblies that entrap DNA to establish chromosomal interactions. Here, we use the budding yeast Saccharomyces cerevisiae to dissect the role of the condensin ATPase and its relationship with cell-cycle-regulated chromosome binding dynamics. ATP hydrolysis-deficient condensin binds to chromosomes but is defective in chromosome condensation and segregation. By modulating the ATPase, we demonstrate that it controls condensin's dynamic turnover on chromosomes. Mitosis-specific phosphorylation of condensin's Smc4 subunit reduces the turnover rate. However, reducing turnover by itself is insufficient to compact chromosomes. We propose that condensation requires fine-tuned dynamic condensin interactions with more than one DNA. These results enhance our molecular understanding of condensin function during chromosome condensation.

Characterization of microsatellite markers for Broussonetia papyrifera (Moraceae).

PREMISE OF THE STUDY: Broussonetia papyrifera (Moraceae) is native to Asia and is used as a medicinal plant and as a source of fiber for making paper. It was dispersed into the Pacific region as a fiber source for making nonwoven textiles (barkcloth). Microsatellites were developed to trace the human-mediated dispersal of this species into the Pacific region. METHODS AND RESULTS: A set of 36 microsatellites was isolated and initially assayed on 10 accessions to assess polymorphism. We found that 20 markers were polymorphic, with the number of alleles per marker ranging from four to 35 in 70 accessions genotyped from three Asian populations. Observed and expected heterozygosities ranged from 0.04 to 0.85 and from 0.19 to 0.94, respectively. These markers were tested in four Moraceae species and one Rosaceae species. CONCLUSIONS: These markers will be useful for the assessment of genetic diversity in B. papyrifera. They show low transferability to other species tested.

Rgf1p (Rho1p GEF) is required for double-strand break repair in fission yeast.

Rho GTPases are conserved molecules that control cytoskeletal dynamics. These functions are expedited by Rho GEFs that stimulate the release of GDP to enable GTP binding, thereby allowing Rho proteins to initiate intracellular signaling. How Rho GEFs and Rho GTPases protect cells from DNA damage is unknown. Here, we explore the extreme sensitivity of a deletion mutation in the Rho1p exchange factor Rgf1p to the DNA break/inducing antibiotic phleomycin (Phl). The Rgf1p mutant cells are defective in reentry into the cell cycle following the induction of severe DNA damage. This phenotype correlates with the inability of rgf1Δ cells to efficiently repair fragmented chromosomes after Phl treatment. Consistent with this observation Rad11p (ssDNA binding protein, RPA), Rad52p, Rad54p and Rad51p, which facilitate strand invasion in the process of homology-directed repair (HDR), are permanently stacked in Phl-induced foci in rgf1Δ cells. These phenotypes are phenocopied by genetic inhibition of Rho1p. Our data provide evidence that Rgf1p/Rho1p activity positively controls a repair function that confers resistance against the anti-cancer drug Phl.

Structure of the cohesin loader Scc2.

The functions of cohesin are central to genome integrity, chromosome organization and transcription regulation through its prevention of premature sister-chromatid separation and the formation of DNA loops. The loading of cohesin onto chromatin depends on the Scc2-Scc4 complex; however, little is known about how it stimulates the cohesion-loading activity. Here we determine the large 'hook' structure of Scc2 responsible for catalysing cohesin loading. We identify key Scc2 surfaces that are crucial for cohesin loading in vivo. With the aid of previously determined structures and homology modelling, we derive a pseudo-atomic structure of the full-length Scc2-Scc4 complex. Finally, using recombinantly purified Scc2-Scc4 and cohesin, we performed crosslinking mass spectrometry and interaction assays that suggest Scc2-Scc4 uses its modular structure to make multiple contacts with cohesin.

Evidence for cohesin sliding along budding yeast chromosomes.

The ring-shaped cohesin complex is thought to topologically hold sister chromatids together from their synthesis in S phase until chromosome segregation in mitosis. How cohesin stably binds to chromosomes for extended periods, without impeding other chromosomal processes that also require access to the DNA, is poorly understood. Budding yeast cohesin is loaded onto DNA by the Scc2-Scc4 cohesin loader at centromeres and promoters of active genes, from where cohesin translocates to more permanent places of residence at transcription termination sites. Here we show that, at the GAL2 and MET17 loci, pre-existing cohesin is pushed downstream along the DNA in response to transcriptional gene activation, apparently without need for intermittent dissociation or reloading. We observe translocation intermediates and find that the distribution of most chromosomal cohesin is shaped by transcription. Our observations support a model in which cohesin is able to slide laterally along chromosomes while maintaining topological contact with DNA. In this way, stable cohesin binding to DNA and enduring sister chromatid cohesion become compatible with simultaneous underlying chromosomal activities, including but maybe not limited to transcription.

Structural Studies Reveal the Functional Modularity of the Scc2-Scc4 Cohesin Loader.

The remarkable accuracy of eukaryotic cell division is partly maintained by the cohesin complex acting as a molecular glue to prevent premature sister chromatid separation. The loading of cohesin onto chromosomes is catalyzed by the Scc2-Scc4 loader complex. Here, we report the crystal structure of Scc4 bound to the N terminus of Scc2 and show that Scc4 is a tetratricopeptide repeat (TPR) superhelix. The Scc2 N terminus adopts an extended conformation and is entrapped by the core of the Scc4 superhelix. Electron microscopy (EM) analysis reveals that the Scc2-Scc4 loader complex comprises three domains: a head, body, and hook. Deletion studies unambiguously assign the Scc2N-Scc4 as the globular head domain, whereas in vitro cohesin loading assays show that the central body and the hook domains are sufficient to catalyze cohesin loading onto circular DNA, but not chromatinized DNA in vivo, suggesting a possible role for Scc4 as a chromatin adaptor.

The putative exchange factor Gef3p interacts with Rho3p GTPase and the septin ring during cytokinesis in fission yeast.

The small GTP-binding proteins of the Rho family and its regulatory proteins play a central role in cytokinetic actomyosin ring assembly and cytokinesis. Here we show that the fission yeast guanine nucleotide exchange factor Gef3p interacts with Rho3p at the division site. Gef3p contains a putative DH homology domain and a BAR/IMD-like domain. The protein localized to the division site late in mitosis, where it formed a ring that did not constrict with actomyosin ring (cytokinetic actomyosin ring) invagination; instead, it split into a double ring that resembled the septin ring. Gef3p co-localized with septins and Mid2p and required septins and Mid2p for its localization. Gef3p interacts physically with the GTP-bound form of Rho3p. Although Gef3p is not essential for cell separation, the simultaneous disruption of gef3(+) and Rho3p-interacting proteins, such as Sec8p, an exocyst component, Apm1p, a subunit of the clathrin adaptor complex or For3p, an actin-polymerizing protein, yielded cells with strong defects in septation and polarity respectively. Our results suggest that interactions between septins and Rho-GEFs provide a new targeting mechanism for GTPases in cytokinesis, in this case probably contributing to Rho3p function in vesicle tethering and vesicle trafficking in the later steps of cell separation.

The checkpoint-dependent nuclear accumulation of Rho1p exchange factor Rgf1p is important for tolerance to chronic replication stress.

Guanine nucleotide exchange factors control many aspects of cell morphogenesis by turning on Rho-GTPases. The fission yeast exchange factor Rgf1p (Rho gef1) specifically regulates Rho1p during polarized growth and localizes to cortical sites. Here we report that Rgf1p is relocalized to the cell nucleus during the stalled replication caused by hydroxyurea (HU). Import to the nucleus is mediated by a nuclear localization sequence at the N-terminus of Rgf1p, whereas release into the cytoplasm requires two leucine-rich nuclear export sequences at the C-terminus. Moreover, Rgf1p nuclear accumulation during replication arrest depends on the 14-3-3 chaperone Rad24p and the DNA replication checkpoint kinase Cds1p. Both proteins control the nuclear accumulation of Rgf1p by inhibition of its nuclear export. A mutant, Rgf1p-9A, that substitutes nine serine potential phosphorylation Cds1p sites for alanine fails to accumulate in the nucleus in response to replication stress, and this correlates with a severe defect in survival in the presence of HU. In conclusion, we propose that the regulation of Rgf1p could be part of the mechanism by which Cds1p and Rad24p promote survival in the presence of chronic replication stress. It will be of general interest to understand whether the same is true for homologues of Rgf1p in budding yeast and higher eukaryotes.