Mitotic chromosomes are compacted laterally by KIF4 and condensin and axially by topoisomerase IIα

© 2012 Samejima et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication dateMitotic chromosome formation involves a relatively minor condensation of the chromatin volume coupled with a dramatic reorganization into the characteristic "X" shape. Here we report results of a detailed morphological analysis, which revealed that chromokinesin KIF4 cooperated in a parallel pathway with condensin complexes to promote the lateral compaction of chromatid arms. In this analysis, KIF4 and condensin were mutually dependent for their dynamic localization on the chromatid axes. Depletion of either caused sister chromatids to expand and compromised the "intrinsic structure" of the chromosomes (defined in an in vitro assay), with loss of condensin showing stronger effects. Simultaneous depletion of KIF4 and condensin caused complete loss of chromosome morphology. In these experiments, topoisomerase IIα contributed to shaping mitotic chromosomes by promoting the shortening of the chromatid axes and apparently acting in opposition to the actions of KIF4 and condensins. These three proteins are major determinants in shaping the characteristic mitotic chromosome morphology

Promotion of healthy lifestyles: strategies and scenarios

Objetivo: analizar las estrategias de promoción de la salud para el fomento de Estilos de Vida Saludables en escenarios de familia, trabajo, comunidad, educación y sector sanitario. Método: estudio descriptivo a partir de la revisión y análisis sistemático de estudios originales primarios sobre estrategias de promoción de la salud y estilos de vida saludables, haciendo uso de la lista de control PRISMA. Resultados: se identificaron tres estrategias de PS para el fomento de EVS, estas se basaron en información, educación, cambio de actitudes, fortalecimiento de la autoestima y toma de decisiones a través de salud móvil, técnicas de motivación, talleres prácticos y psicoeducación. Conclusiones: el desarrollo de estrategias que promueven estilos de vida saludables es incipiente en escenarios como el lugar de trabajo y la familia, lo cual genera una baja cobertura poblacional y demanda acciones interdisciplinarias desde diferentes campos como el de la Psicología de la Salud.Objective: To analyze Health Promotion (HP) strategies for the encouragement of healthy lifestyles (EHL) in family, work, community, education and the health sector scenarios. Method: descriptive study based on the systematic review and analysis of primary original studies on health promotion strategies in healthy lifestyles, making use of the PRISMA checklist. Results: three HP strategies were identified for the promotion of EHL which were based on information, education, change of attitudes, strengthening of self-esteem and decision making through mobile health, motivation techniques, practical workshops and psychoeducation. Conclusions: the development of strategies that promote healthy lifestyles is incipient in scenarios such as the workplace and the family, which generates low population coverage and demands interdisciplinary actions from different fields such as the Psychology of health

Mammalian cell entry genes in Streptomyces may provide clues to the evolution of bacterial virulence

Understanding the evolution of virulence is key to appreciating the role specific loci play in pathogenicity. Streptomyces species are generally non-pathogenic soil saprophytes, yet within their genome we can find homologues of virulence loci. One example of this is the mammalian cell entry (mce) locus, which has been characterised in Mycobacterium tuberculosis. To investigate the role in Streptomyces we deleted the mce locus and studied its impact on cell survival, morphology and interaction with other soil organisms. Disruption of the mce cluster resulted in virulence towards amoebae (Acanthamoeba polyphaga) and reduced colonization of plant (Arabidopsis) models, indicating these genes may play an important role in Streptomyces survival in the environment. Our data suggest that loss of mce in Streptomyces spp. may have profound effects on survival in a competitive soil environment, and provides insight in to the evolution and selection of these genes as virulence factors in related pathogenic organisms

DNA methyltransferase 3b preferentially associates with condensed chromatin

In mammals, DNA methylation is catalyzed by DNA methyltransferases (DNMTs) encoded by Dnmt1, Dnmt3a and Dnmt3b. Since, the mechanisms of regulation of Dnmts are still largely unknown, the physical interaction between Dnmt3b and chromatin was investigated in vivo and in vitro. In embryonic stem cell nuclei, Dnmt3b preferentially associated with histone H1-containing heterochromatin without any significant enrichment of silent-specific histone methylation. Recombinant Dnmt3b preferentially associated with nucleosomal DNA rather than naked DNA. Incorporation of histone H1 into nucleosomal arrays promoted the association of Dnmt3b with chromatin, whereas histone acetylation reduced Dnmt3b binding in vitro. In addition, Dnmt3b associated with histone deacetylase SirT1 in the nuclease resistant chromatin. These findings suggest that Dnmt3b is preferentially recruited into hypoacetylated and condensed chromatin. We propose that Dnmt3b is a ‘reader’ of higher-order chromatin structure leading to gene silencing through DNA methylation

Treatment of breast cancer cells with DNA demethylating agents leads to a release of Pol II stalling at genes with DNA-hypermethylated regions upstream of TSS

Inactivation of tumor suppressor genes plays an important role in tumorigenesis, and epigenetic modifications such as DNA methylation are frequently associated with transcriptional repression. Here, we show that gene silencing at selected genes with signs of DNA hypermethylation in breast cancer cells involves Pol II stalling. We studied several repressed genes with DNA hypermethylation within a region 1-kb upstream of the transcriptional start site that were upregulated after treatment with DNA demethylating agents, such as Azacytidine and several natural products. All those selected genes had stalled Pol II at their transcriptional start site and showed enhanced ser2 phosphorylated Pol II and elevated transcripts after drug treatment indicating successful elongation. In addition, a decrease of the epigenetic regulator LSH in a breast cancer cell line by siRNA treatment reduced DNA methylation and overcame Pol II stalling, whereas overexpression of LSH in a normal breast epithelial cell line increased DNA methylation and resulted in repression. Decrease of LSH was associated with reduced DNMT3b binding to promoter sequences, and depletion of DNMT3b by siRNA could release Pol II suggesting that DNMT3b is functionally involved. The release of paused Pol II was accompanied by a dynamic switch from repressive to active chromatin marks. Thus release of Pol II stalling can act as a mechanism for gene reactivation at specific target genes after DNA demethylating treatment in cancer cells

Lsh controls Hox gene silencing during development

Polycomb-mediated repression and DNA methylation are important epigenetic mechanisms of gene silencing. Recent evidence suggests a functional link between the polycomb repressive complex (PRC) and Dnmts in cancer cells. Here we provide evidence that Lsh, a regulator of DNA methylation, is also involved in normal control of PRC-mediated silencing during embryogenesis. We demonstrate that Lsh, a SNF2 homolog, can associate with some Hox genes and regulates Dnmt3b binding, DNA methylation, and silencing of Hox genes during development. Moreover, Lsh can associate with PRC1 components and influence PRC-mediated histone modifications. Thus Lsh is part of a physiological feedback loop that reinforces DNA methylation and silencing of PRC targets

Lymphoid-specific helicase (HELLS) is essential for meiotic progression in mouse spermatocytes

Lymphoid-specific helicase (HELLS; also known as LSH) is a member of the SNF2 family of chromatin remodeling proteins. Because Hells-null mice die at birth, a phenotype in male meiosis cannot be studied in these animals. Allografting of testis tissue from Hells(-/-) to wild-type mice was employed to study postnatal germ cell differentiation. Testes harvested at Day 18.5 of gestation from Hells(-/-), Hells(+/-), and Hells(+/+) mice were grafted ectopically to immunodeficient mice. Bromodeoxyuridine incorporation at 1 wk postgrafting revealed fewer dividing germ cells in grafts from Hells(-/-) than from Hells(+/+) mice. Whereas spermatogenesis proceeded through meiosis with round spermatids in grafts from Hells heterozygote and wild-type donor testes, spermatogenesis arrested at stage IV, and midpachytene spermatocytes were the most advanced germ cell type in grafts from Hells(-/-) mice at 4, 6, and 8 wk after grafting. Analysis of meiotic configurations at 22 days posttransplantation revealed an increase in Hells(-/-) spermatocytes with abnormal chromosome synapsis. These results indicate that in the absence of HELLS, proliferation of spermatogonia is reduced and germ cell differentiation arrested at the midpachytene stage, implicating an essential role for HELLS during male meiosis. This study highlights the utility of testis tissue grafting to study spermatogenesis in animal models that cannot reach sexual maturit