The Biochemistry of Mitosis

In this article, we will discuss the biochemistry of mitosis in eukaryotic cells. We will focus on conserved principles that, importantly, are adapted to the biology of the organism. It is vital to bear in mind that the structural requirements for division in a rapidly dividing syncytial Drosophila embryo, for example, are markedly different from those in a unicellular yeast cell. Nevertheless, division in both systems is driven by conserved modules of antagonistic protein kinases and phosphatases, underpinned by ubiquitin-mediated proteolysis, which create molecular switches to drive each stage of division forward. These conserved control modules combine with the self-organizing properties of the subcellular architecture to meet the specific needs of the cell. Our discussion will draw on discoveries in several model systems that have been important in the long history of research on mitosis, and we will try to point out those principles that appear to apply to all cells, compared with those in which the biochemistry has been specifically adapted in a particular organism.The aim of mitosis is to separate the genome and ensure that the two daughter cells inherit an equal and identical complement of chromosomes (Yanagida 2014). To achieve this, eukaryotic cells completely reorganize their microtubules to build a mitotic spindle that pulls apart the sister chromatids after the cohesin complexes are cut (see Cheeseman 2014; Hirano 2015; Reber and Hyman 2015; Westhorpe and Straight 2015) and, subsequently, use the actin cytoskeleton to divide the cell into two (cytokinesis) (see D’Avino et al. 2015). In some cells, such as in budding and fission yeasts, the spindle is built within the nucleus (closed mitosis), whereas in others, the nuclear envelope breaks down and the condensed chromosomes are captured by microtubules in the cytoplasm (open mitosis). This difference in the spatial organization of the mitotic cell has ramifications for the machinery controlling mitosis. In particular, the breakdown of the nuclear compartment disrupts the guanosine triphosphate (GTP)–guanosine diphosphate (GDP) gradient of the small GTPase called Ran. Ran usually controls nuclear-cytoplasmic transport through the importin chaperones; Ran-GDP in the cytoplasm promotes binding to nuclear transport substrates, whereas Ran-GTP in the nucleus promotes their dissociation (Güttler and Görlich 2011). As a result of nuclear envelope breakdown (NEBD), another Ran-GTP gradient is generated around the chromosomes, to which the RCC1 GTP-exchange factor binds (Clarke 2008). This Ran-GTP gradient is important for the interaction between microtubules and chromosomes because the high Ran-GTP levels around chromosomes promote the dissociation between the importin β chaperone and its binding partners, several of which help to stabilize or nucleate microtubules (Carazo-Salas et al. 1999; Kalab et al. 1999; Gruss et al. 2001; Wilde et al. 2001; Yokoyama et al. 2008).The dramatic reorganization of the cell at mitosis must be coordinated in both time and space. There are several key temporal events: entry to mitosis, sister chromatid separation, and mitotic exit, and these are effectively made unidirectional by the biochemical machinery. We will discuss the biochemistry behind each of these temporal events, in turn, but it is important to emphasize that the control mechanisms are also spatially organized. Our understanding of this spatial organization has improved dramatically with advances in the technology to detect gradients of activity in cells, and this has revealed the importance of local gradients of antagonistic protein kinases and phosphatases, GTP-binding protein regulators, and ubiquitin ligases and deubiquitylases, to name only a few of the more prominent examples (reviewed in Pines and Hagan 2011).     

Social Costs of Iron Deficiency Anemia in 6–59-Month-Old Children in India

Introduction

Inadequate nutrition has a severe impact on health in India. According to the WHO, iron deficiency is the single most important nutritional risk factor in India, accounting for more than 3% of all disability-adjusted life years (DALYs) lost. We estimate the social costs of iron deficiency anemia (IDA) in 6–59-month-old children in India in terms of intangible costs and production losses.

Materials and Methods

We build a health economic model estimating the life-time costs of a birth cohort suffering from IDA between the ages of 6 and 59 months. The model is stratified by 2 age groups (6–23 and 24–59-months), 2 geographical areas (urban and rural), 10 socio-economic strata and 3 degrees of severity of IDA (mild, moderate and severe). Prevalence of anemia is calculated with the last available National Family Health Survey. Information on the health consequences of IDA is extracted from the literature.

Results

IDA prevalence is 49.5% in 6–23-month-old and 39.9% in 24–58-month-old children. Children living in poor households in rural areas are particularly affected but prevalence is high even in wealthy urban households. The estimated yearly costs of IDA in 6–59-month-old children amount to intangible costs of 8.3 m DALYs and production losses of 24,001 m USD, equal to 1.3% of gross domestic product. Previous calculations have considerably underestimated the intangible costs of IDA as the improved WHO methodology leads to a threefold increase of DALYs due to IDA.

Conclusion

Despite years of iron supplementation programs and substantial economic growth, IDA remains a crucial public health issue in India and an obstacle to the economic advancement of the poor. Young children are especially vulnerable due to the irreversible effects of IDA on cognitive development. Our research may contribute to the design of new effective interventions aiming to reduce IDA in early childhood.     

Prevalence of Pulmonary Tuberculosis among Prison Inmates in Ethiopia,a Cross-Sectional Study

Setting

Tuberculosis (TB) is one of the major health problems in prisons.

Objective

This study was done to assess the prevalence and determinants of active tuberculosis in Ethiopian prisons.

Design

A cross-sectional study was conducted from January 2013 to December 2013 in 13 zonal prisons. All incarcerated inmates underwent TB symptom screening according to WHO criteria. From identified TB-suspects two sputum samples were analyzed using smear microscopy and solid culture. A standardized questionnaire assessing TB risk factors was completed for each TB suspect.

Results

765 (4.9%) TB suspects were identified among 15,495 inmates. 51 suspects were already on anti-TB treatment (6.67%) and 20 (2.8%) new culture-confirmed TB cases were identified in the study, resulting in an overall TB prevalence of 458.1/100,000 (95%CI: 350-560/100,000). Risk factors for active TB were alcohol consumption, contact with a TB case before incarceration and no window in prison cell. HIV prevalence was not different between TB suspects and active TB cases. Further, the TB burden in prisons increased with advancing distance from the capital Addis Ababa.

Conclusions

The overall TB prevalence in Ethiopian prisons was high and extremely variable among different prisons. TB risk factors related to conditions of prison facilities and the impact of implemented TB control measures need to be further studied in order to improve TB control among inmates.     

A novel ex vivo set-up for dynamic long-term characterization of processes on mucosal interfaces by confocal imaging and simultaneous cytokine measurements

We present a novel organ-explant imaging system for easy and cost-effective extended-time observation of host-pathogen interactions at mucosal interfaces. Data are complemented by parallel cytokine measurements at high temporal resolution. The set-up is based on a custom-built reusable organ chamber compatible with standard microscopes. Luminal and basal side of the explanted mucosa are connected to separate channels for optimized incubation and cytokine measurements, oxygen is provided via membrane oxygenation. Dynamic imaging with confocal microscopy permits a detailed analysis of the dynamics of pathogen-host cell interactions at the mucosal interface and the neighbouring tissue at high resolution. The system can be applied to various hollow organs with few modifications. Here we present first applications to study representative infections such as uropathogenic Escherichia coli (UPEC) infections in the urinary bladder or amoebiasis of the colon by using mouse organs. We show (i) intracellular bacteria in UPEC infections, (ii) phagocytic events on tissue during infection, as well as (iii) tissue invasion of virulent protozoans into epithelia. The versatility of this system and its higher degree of control in comparison with both traditional explant microscopy and in vivo two photon imaging solutions make it a valuable and easy-to-use addition to other current imaging techniques.     

EVI1 Inhibits Apoptosis Induced by Antileukemic Drugs via Upregulation of CDKN1A/p21/WAF in Human Myeloid Cells

Overexpression of ecotropic viral integration site 1 (EVI1) is associated with aggressive disease in acute myeloid leukemia (AML). Despite of its clinical importance, little is known about the mechanism through which EVI1 confers resistance to antileukemic drugs. Here, we show that a human myeloid cell line constitutively overexpressing EVI1 after infection with a retroviral vector (U937_EVI1) was partially resistant to etoposide and daunorubicin as compared to empty vector infected control cells (U937_vec). Similarly, inducible expression of EVI1 in HL-60 cells decreased their sensitivity to daunorubicin. Gene expression microarray analyses of U937_EVI1 and U937_vec cells cultured in the absence or presence of etoposide showed that 77 and 419 genes were regulated by EVI1 and etoposide, respectively. Notably, mRNA levels of 26 of these genes were altered by both stimuli, indicating that EVI1 regulated genes were strongly enriched among etoposide regulated genes and vice versa. One of the genes that were induced by both EVI1 and etoposide was CDKN1A/p21/WAF, which in addition to its function as a cell cycle regulator plays an important role in conferring chemotherapy resistance in various tumor types. Indeed, overexpression of CDKN1A in U937 cells mimicked the phenotype of EVI1 overexpression, similarly conferring partial resistance to antileukemic drugs.     

External exposure of deciduous tooth enamel to photons: dose conversion coefficients for standard radiation fields

Dose conversion coefficients for teeth of children were computed for external photon sources by means of Monte Carlo methods using a modified MIRD-type mathematical phantom of a 5-year-old child. The tooth region is separated into eight smaller regions that represent incisors, canines, first and second molars. Each of these sub-regions is separated into enamel and dentin parts. Dose conversion coefficients were computed as ratio of absorbed dose in the enamel and air kerma. They are given for unidirectional (AP, PA, RLAT, LLAT), rotational (ROT) and isotropic (ISO) photon sources in the energy range from 10 keV to 10 MeV. All computations were performed with the MCNP4 code including coupled electron-photon transport. The computed coefficients demonstrate a significant non-linearity versus photon energy, which is more pronounced than that observed for adult phantoms. Due to this non-linearity, use of the EPR-measured doses in human teeth requires information on the incident photon fluence spectra. The data presented can be used for assessment of public exposure.