Elite endurance athletes possess a high capacity for whole-body maximal fat oxidation (MFO). The aim was to investigate the determinants of a high MFO in endurance athletes. The hypotheses were that augmented MFO in endurance athletes is related to concomitantly increments of skeletal muscle mitochondrial volume density (Mito ) and mitochondrial fatty acid oxidation (FAO ), that is, quantitative mitochondrial adaptations as well as intrinsic FAO per mitochondria, that is, qualitative adaptations. Eight competitive male cross-country skiers and eight untrained controls were compared in the study. A graded exercise test was performed to determine MFO, the intensity where MFO occurs (Fat ), and . Skeletal muscle biopsies were obtained to determine Mito (electron microscopy), FAO , and OXPHOS (high-resolution respirometry). The following were higher (P < 0.05) in endurance athletes compared to controls: MFO (mean [95% confidence intervals]) (0.60 g/min [0.50-0.70] vs 0.32 [0.24-0.39]), Fat (46% [44-47] vs 35 [34-37]), (71 mL/min/kg [69-72] vs 48 [47-49]), Mito (7.8% [7.2-8.5] vs 6.0 [5.3-6.8]), FAO (34 pmol/s/mg muscle ww [27-40] vs 21 [17-25]), and OXPHOS (108 pmol/s/mg muscle ww [104-112] vs 69 [68-71]). Intrinsic FAO (4.0 pmol/s/mg muscle w.w/Mito [2.7-5.3] vs 3.3 [2.7-3.9]) and OXPHOS (14 pmol/s/mg muscle ww/Mito [13-15] vs 11 [10-13]) were, however, similar in the endurance athletes and untrained controls. MFO and Mito correlated (r = 0.504, P < 0.05) in the endurance athletes. A strong correlation between Mito and MFO suggests that expansion of Mito might be rate-limiting for MFO in the endurance athletes. In contrast, intrinsic mitochondrial changes were not associated with augmented MFO.

SummaryAll organisms evolved defense mechanisms to counteract oxidative stress and buildup of reactive oxygen species (ROS). To test whether a potentially conserved mechanism exists for the rapid response, we investigated immediate metabolic dynamics of Escherichia coli, yeast, and human dermal fibroblasts to oxidative stress that we found to be conserved between species. To elucidate the regulatory mechanisms that implement this metabolic response, we developed mechanistic kinetic models for each organism's central metabolism and systematically tested activation and inactivation of each irreversible reaction by each metabolite. This ensemble modeling predicts in vivo relevant metabolite-enzyme interactions based on their ability to quantitatively describe metabolite dynamics. All three species appear to inhibit their oxidative pentose phosphate pathway during normal growth by the redox cofactor NADPH and relieve this inhibition to increase the pathway flux for detoxification of ROS during stress, with the sole exception of yeast when exposed to high levels of stress.

A data-driven energy ecan in the immediate vicinity of the 7 pair production tbreshold has been performed using the Beijing Spectrometer at the Beijing Electron-PositronCollider. Approximately 5 pb-' of data, distributed over 12 ecan points, have been collected. A previous maee value for the 7 lepton, obtained using only the ep final state, has been published. In this paper, the final BES result on the maes measurement is presented. The analysis is based on the combined data from the ee, ep, eh, VW, ph, and hh final states, where h denotes a charged ?( or K. A maximum likelihood fit to the r pair production cross section data yields the value rn, = 1776.96+~:~~!~:~~ MeV. PACS number(s): 14.60.Fg, 13.1O.+q

Two mitotic Cyclins, A and B, exist in higher eukaryotes, but their specialised functions in mitosis are poorly understood. Using degron tags we analyse how acute depletion of these proteins affects mitosis. Loss of Cyclin A in G2-phase prevents the initial activation of Cdk1. Cells lacking Cyclin B can enter mitosis and phosphorylate most mitotic proteins, because of parallel PP2A:B55 phosphatase inactivation by Greatwall kinase. The final barrier to mitotic establishment corresponds to nuclear envelope breakdown that requires a decisive shift in the balance of Cdk1 and PP2A:B55 activity. Beyond this point Cyclin B/Cdk1 is essential to phosphorylate a distinct subset mitotic Cdk1 substrates that are essential to complete cell division. Our results identify how Cyclin A, B and Greatwall coordinate mitotic progression by increasing levels of Cdk1-dependent substrate phosphorylation. 3 Main TextCdk1 phosphorylates over 1000 proteins 1,2 within the brief 20-30 minute window of mitotic entry, triggering centrosome separation and chromosome condensation in prophase, followed by nuclear envelope breakdown (NEBD) and mitotic spindle formation in prometaphase, and the alignment of bi-oriented sister chromatids at the metaphase plate 3 . Binding of a Cyclin partner is critical for allosteric activation of CDKs. Two families of mitotic Cyclins, termed A and B, work with Cdk1 to orchestrate mitotic entry in higher eukaryotes 4,5 . Despite the central importance of these proteins for cell cycle control, the functional specialisation of mammalian A and B-type Cyclins remains unclear. Following the depletion of maternal pools of early embryonic Cyclin A1 and B3, somatic mammalian cells express one A-type Cyclin, A2, and two B-type cyclins, B1 and B2. Genetic depletion in mice suggests an essential role for Cyclin A2 for development, but not for embryonic fibroblast proliferation 6 . Depletion of Human Cyclin A2 by siRNA delays mitotic entry, and this is further enhanced by co-depletion of Cyclin B1 7-9 . Likewise, work in mammalian cell extracts documented how Cyclin A synergises with Cyclin B to control the mitotic entry threshold at the level for Cdk1 activation 10 . A mechanism involving Plk1 activation has been suggested 11,12 , although an essential role of Plk1 in the G2/M transition remains contentious 13 . Likewise, work in mammalian cell extracts documented how Cyclin A synergises with Cyclin B to control the mitotic entry threshold at the level for Cdk1 activation 10 . A confounding factor in the genetic analysis of Cyclin A2 has been its dual role in S-phase and mitosis 14 , making it difficult to directly investigate G2 specific defects. Murine Cyclin B1 is essential for development 15 and critical for mitotic entry in early mouse embryos 16 . Conversely, mice lacking Cyclin B2 live healthily, without apparent defects 15 . These results stand in stark contrast to observations from experiments involving siRNA depletion of B-type Cyclins in human cancer cell lines that show surprisingly mild mitotic entry defects 9,1...

Synthetic biology relies on rapid and efficient methods to stably integrate DNA payloads encoding for synthetic biological systems into the genome of living cells. The size of designed biological systems increases with their complexity, and novel methods are needed that enable efficient and simultaneous integration of multiple payloads into single cells. By assembling natural and synthetic protein–protein dimerization domains, we have engineered a set of multipartite transcription factors for driving heterologous target gene expression. With the distribution of single parts of multipartite transcription factors on piggyback transposon-based donor plasmids, we have created a logic genome integration control (LOGIC) system that allows for efficient one-step selection of stable mammalian cell lines with up to three plasmids. LOGIC significantly enhances the efficiency of multiplexed payload integration in mammalian cells compared to traditional cotransfection and may advance cell line engineering in synthetic biology and biotechnology.

Based upon a comprehensive analysis of current literature and by combining a molecular biology and a sports science perspective, this review examines (1) if a correlation between physical activity load and telomere length (TL) exists, and (2) comprehensively analyses and integrates molecular pathways regulating exercise dependent TL dynamics. The focus is on TL in leukocytes and muscle tissue in middle to advanced aged subjects. Regarding item (1), a strong tendency for an increase in mean leukocyte TL was found for exercise energy expenditures up to about 2∙103 kcal/week, while for higher activity levels no conclusive statement can be made. Conversely, research on skeletal muscle TL so far is quite limited but suggests that physical exercise with prolonged eccentric muscle contractions rather acts to shorten telomeres, while sports with little eccentric contractions might rather act to lengthen telomeres. As to item (2), a model for hypothetical pathways for exercise dependent telomerase activity regulation is proposed by consolidating findings of different studies in different cells. Consistent with this pathway model, various studies report increased telomerase transcription or activation by exercise. Moreover, a qualitative overall model for endurance exercise related TL dynamics is presented. It considers telomeres as dynamic structures in equilibrium between telomere shortening (e.g., cellular turnover, oxidative stress, inflammation) and telomere lengthening (e.g., telomerase activity, telomerase recruitment) effects. A negative feedback-loop mediated by enhanced telomerase recruitment to short telomeres is assumed to counteract too excessive TL alterations. Finally, a proposal is put forth for future research on exercise dependent telomere dynamics by adopting a systems biology approach to develop mathematical models that properly integrate the complexity of the interacting variables.

The mammalian cell cycle is regulated by a well-studied but complex biochemical reaction system. Computational models provide a particularly systematic and systemic description of the mechanisms governing mammalian cell cycle control. By combining both state-of-the-art multiplexed experimental methods and powerful computational tools, this work aims at improving on these models along four dimensions: model structure, validation data, validation methodology and model reusability. We developed a comprehensive model structure of the full cell cycle that qualitatively explains the behaviour of human retinal pigment epithelial-1 cells. To estimate the model parameters, time courses of eight cell cycle regulators in two compartments were reconstructed from single cell snapshot measurements. After optimisation with a parallel global optimisation metaheuristic we obtained excellent agreements between simulations and measurements. The PEtab specification of the optimisation problem facilitates reuse of model, data and/or optimisation results. Future perturbation experiments will improve parameter identifiability and allow for testing model predictive power. Such a predictive model may aid in drug discovery for cell cycle-related disorders.