Timing and checkpoints in the regulation of mitotic progression

Accurate chromosome segregation relies on the precise regulation of mitotic progression. Regulation involves control over the timing of mitosis and a spindle assembly checkpoint that links anaphase onset to the completion of chromosome-microtubule attachment. In this paper, we combine live-cell imaging of HeLa cells and protein depletion by RNA interference to examine the functions of the Mad, Bub, and kinetochore proteins in mitotic timing and checkpoint control. We show that the depletion of any one of these proteins abolishes the mitotic arrest provoked by depolymerizing microtubules or blocking chromosome-microtubule attachment with RNAi. However, the normal progress of mitosis is accelerated only when Mad2 or BubR1, but not other Mad and Bub proteins, are inactivated. Moreover, whereas checkpoint control requires kinetochores, the regulation of mitotic timing by Mad2 and BubR1 is kinetochore-independent in fashion. We propose that cytosolic Mad2-BubR1 is essential to restrain anaphase onset early in mitosis when kinetochores are still assembling.     

Single amino acid supplementation in aminoacidopathies: a systematic review

Aminoacidopathies are a group of rare and diverse disorders, caused by the deficiency of an enzyme or transporter involved in amino acid metabolism. For most aminoacidopathies, dietary management is the mainstay of treatment. Such treatment includes severe natural protein restriction, combined with protein substitution with all amino acids except the amino acids prior to the metabolic block and enriched with the amino acid that has become essential by the enzymatic defect. For some aminoacidopathies, supplementation of one or two amino acids, that have not become essential by the enzymatic defect, has been suggested. This so-called single amino acid supplementation can serve different treatment objectives, but evidence is limited. The aim of the present article is to provide a systematic review on the reasons for applications of single amino acid supplementation in aminoacidopathies treated with natural protein restriction and synthetic amino acid mixtures.     

Rapid phospho-turnover by receptor tyrosine kinases impacts downstream signaling and drug binding

Epidermal growth factor receptors (ErbB1-4) are oncogenic receptor tyrosine kinases (RTKs) that regulate diverse cellular processes. In this study, we combine measurement and mathematical modeling to quantify phospho-turnover at ErbB receptors in human cells and to determine the consequences for signaling and drug binding. We find that phosphotyrosine residues on ErbB1 have half-lives of a few seconds and therefore turn over 100-1000 times in the course of a typical immediate-early response to ligand. Rapid phospho-turnover is also observed for EGF-activated ErbB2 and ErbB3, unrelated RTKs, and multiple intracellular adaptor proteins and signaling kinases. Thus, the complexes formed on the cytoplasmic tail of active receptors and the downstream signaling kinases they control are highly dynamic and antagonized by potent phosphatases. We develop a kinetic scheme for binding of anti-ErbB1 drugs to receptors and show that rapid phospho-turnover significantly impacts their mechanisms of action.     

Regenerative potential of human muscle stem cells in chronic inflammation

Introduction

Chronic inflammation is a profound systemic modification of the cellular microenvironment which could affect survival, repair and maintenance of muscle stem cells. The aim of this study was to define the role of chronic inflammation on the regenerative potential of satellite cells in human muscle.

Methods

As a model for chronic inflammation, 11 patients suffering from rheumatoid arthritis (RA) were included together with 16 patients with osteoarthritis (OA) as controls. The mean age of both groups was 64 years, with more females in the RA group compared to the OA group. During elective knee replacement surgery, a muscle biopsy was taken from the distal musculus vastus medialis. Cell populations from four RA and eight OA patients were used for extensive phenotyping because these cell populations showed no spontaneous differentiation and myogenic purity greater than 75% after explantation.

Results

After mononuclear cell explantation, myogenic purity, viability, proliferation index, number of colonies, myogenic colonies, growth speed, maximum number of population doublings and fusion index were not different between RA and OA patients. Furthermore, the expression of proteins involved in replicative and stress-induced premature senescence and apoptosis, including p16, p21, p53, hTERT and cleaved caspase-3, was not different between RA and OA patients. Mean telomere length was shorter in the RA group compared to the OA group.

Conclusions

In the present study we found evidence that chronic inflammation in RA does not affect the in vitro regenerative potential of human satellite cells. Identification of mechanisms influencing muscle regeneration by modulation of its microenvironment may, therefore, be more appropriate.     

Mps1 at kinetochores is essential for female mouse meiosis I

In female meiosis, chromosome missegregations lead to the generation of aneuploid oocytes and can cause the development of trisomies or infertility. Because mammalian female meiosis I is error prone, the full functionality of control mechanisms, such as the spindle assembly checkpoint (SAC), has been put into question. The SAC monitors the correct orientation, microtubule occupancy and tension on proteinaceous structures named kinetochores. Although it has been shown previously that the SAC exists in meiosis I, where attachments are monopolar, the role of microtubule occupancy for silencing the SAC and the importance of certain essential SAC components, such as the kinase Mps1, are unknown in mammalian oocytes. Using a conditional loss-of-function approach, we address the role of Mps1 in meiotic progression and checkpoint control in meiosis I. Our data demonstrate that kinetochore localization of Mps1 is required for the proper timing of prometaphase and is essential for SAC control, chromosome alignment and aurora C localization in meiosis I. The absence of Mps1 from kinetochores severely impairs chromosome segregation in oocyte meiosis I and, therefore, fertility in mice. In addition, we settle a long-standing question in showing that kinetochore-microtubule attachments are present in prometaphase I at a time when most of the SAC protein Mad2 disappears from kinetochores.     

Who likes it hot? A global analysis of the climatic,ecological, and evolutionary determinants of warming tolerance in ants

Effects of climate warming on wild populations of organisms are expected to be greatest at higher latitudes, paralleling greater anticipated increases in temperature in these regions. Yet, these expectations assume that populations in different regions are equally susceptible to the effects of warming. This is unlikely to be the case. Here, we develop a series of predictive models for physiological thermal tolerances in ants based on current and future climates. We found that tropical ants have lower warming tolerances, a metric of susceptibility to climate warming, than temperate ants despite greater increases in temperature at higher latitudes. Using climatic, ecological and phylogenetic data, we refine our predictions of which ants (across all regions) were most susceptible to climate warming. We found that ants occupying warmer and more mesic forested habitats at lower elevations are the most physiologically susceptible to deleterious effects of climate warming. Phylogenetic history was also a strong indicator of physiological susceptibility. In short, we find that ants that live in the canopies of hot, tropical forest are the most at risk, globally, from climate warming. Unfortunately this is where many, perhaps most, ant and other species on Earth live.     

Field site selection: getting it right first time around

The selection of suitable field sites for integrated control of Anopheles mosquitoes using the sterile insect technique (SIT) requires consideration of the full gamut of factors facing most proposed control strategies, but four criteria identify an ideal site: 1) a single malaria vector, 2) an unstructured, relatively low density target population, 3) isolation of the target population and 4) actual or potential malaria incidence. Such a site can exist in a diverse range of situations or can be created. Two contrasting SIT field sites are examined here: the desert-flanked Dongola Reach of the Nile River in Northern State, Sudan, where malaria is endemic, and the island of La Reunion, where autochthonous malaria is rare but risk is persistent. The single malaria-transmitting vector at both sites is Anopheles arabiensis. In Sudan, the target area is a narrow 500 km corridor stretching from the rocky terrain at the Fourth Cataract - just above the new Merowe Dam, to the northernmost edge of the species range, close to Egypt. Vector distribution and temporal changes in density depend on the Nile level, ambient temperature and human activities. On La Reunion, the An. arabiensis population is coastal, limited and divided into three areas by altitude and exposure to the trade winds on the east coast. Mosquito vectors for other diseases are an issue at both sites, but of primary importance on La Reunion due to the recent chikungunya epidemic. The similarities and differences between these two sites in terms of suitability are discussed in the context of area-wide integrated vector management incorporating the SIT.     

Ethical,legal and social aspects of the approach in Sudan

The global malaria situation, especially in Africa, and the problems frequently encountered in chemical control of vectors such as insecticide resistance, emphasize the urgency of research, development and implementation of new vector control technologies that are applicable at regional and local levels. The successful application of the sterile insect technique (SIT) for the control of the New World screwworm Cochliomyia hominivorax and several species of fruit flies has given impetus to the use of this method for suppression or elimination of malaria vectors in some areas of Africa including Northern State of Sudan. The research and development phase of the Northern State feasibility study has been started. Sudanese stakeholders are working side-by-side with the International Atomic Energy Agency in the activities of this important phase. Several ethical, legal and social issues associated with this approach arose during this phase of the project. They need to be seriously considered and handled with care. In this paper, these issues are described, and the current and proposed activities to overcome potential hurdles to ensure success of the project are listed.     

Flexible informatics for linking experimental data to mathematical models via DataRail

MOTIVATION: Linking experimental data to mathematical models in biology is impeded by the lack of suitable software to manage and transform data. Model calibration would be facilitated and models would increase in value were it possible to preserve links to training data along with a record of all normalization, scaling, and fusion routines used to assemble the training data from primary results. RESULTS: We describe the implementation of DataRail, an open source MATLAB-based toolbox that stores experimental data in flexible multi-dimensional arrays, transforms arrays so as to maximize information content, and then constructs models using internal or external tools. Data integrity is maintained via a containment hierarchy for arrays, imposition of a metadata standard based on a newly proposed MIDAS format, assignment of semantically typed universal identifiers, and implementation of a procedure for storing the history of all transformations with the array. We illustrate the utility of DataRail by processing a newly collected set of approximately 22 000 measurements of protein activities obtained from cytokine-stimulated primary and transformed human liver cells. AVAILABILITY: DataRail is distributed under the GNU General Public License and available at http://code.google.com/p/sbpipeline/     

Host-specific cues cause differential attractiveness of Kenyan men to the African malaria vector Anopheles gambiae

Background  

Many studies have suggested that variability in the attractiveness of humans to host-seeking mosquitoes is caused by differences in the make-up of body emanations, and olfactory signals in particular. Most investigations have either been laboratory-based, utilising odour obtained from sections of the body, or have been done in the field with sampling methods that do not discriminate between visual, physical and chemical cues of the host. Accordingly, evidence for differential attractiveness based on body emanations remains sparse in spite of the far-reaching epidemiological implications of this phenomenon.