Stochastic multi-scale models of competition within heterogeneous cellular populations: simulation methods and mean-field analysis

We propose a modelling framework to analyse the stochastic behaviour of heterogeneous, multi-scale cellular populations. We illustrate our methodology with a particular example in which we study a population with an oxygen-regulated proliferation rate. Our formulation is based on an age-dependent stochastic process. Cells within the population are characterised by their age. The age-dependent (oxygen-regulated) birth rate is given by a stochastic model of oxygen-dependent cell cycle progression. We then formulate an age-dependent birth-and-death process, which dictates the time evolution of the cell population. The population is under a feedback loop which controls its steady state size: cells consume oxygen which in turns fuels cell proliferation. We show that our stochastic model of cell cycle progression allows for heterogeneity within the cell population induced by stochastic effects. Such heterogeneous behaviour is reflected in variations in the proliferation rate. Within this set-up, we have established three main results. First, we have shown that the age to the G1/S transition, which essentially determines the birth rate, exhibits a remarkably simple scaling behaviour. This allows for a huge simplification of our numerical methodology. A further result is the observation that heterogeneous populations undergo an internal process of quasi-neutral competition. Finally, we investigated the effects of cell-cycle-phase dependent therapies (such as radiation therapy) on heterogeneous populations. In particular, we have studied the case in which the population contains a quiescent sub-population. Our mean-field analysis and numerical simulations confirm that, if the survival fraction of the therapy is too high, rescue of the quiescent population occurs. This gives rise to emergence of resistance to therapy since the rescued population is less sensitive to therapy

Minimum Action Path theory reveals the details of stochastic biochemical transitions out of oscillatory cellular states

Cell state determination is the outcome of intrinsically stochastic biochemical reactions. Tran- sitions between such states are studied as noise-driven escape problems in the chemical species space. Escape can occur via multiple possible multidimensional paths, with probabilities depending non-locally on the noise. Here we characterize the escape from an oscillatory biochemical state by minimizing the Freidlin-Wentzell action, deriving from it the stochastic spiral exit path from the limit cycle. We also use the minimized action to infer the escape time probability density function

Exploring Students’ Beliefs about Autonomy in an EFL Setting

89 páginasThe present study aims to explore the beliefs students hold about autonomy in reference to responsibility, ability and willingness to plan, motivate and evaluate learning. This study was carried out at Universidad Cooperativa de Colombia, Pasto campus, where English language courses require learners to approach learning from an autonomous perspective. However, no previous studies have been carried out to determine whether or not learners have the characteristics of autonomous learners. A total of 432 students participated in the study. They answered a 30 closed-item multiple choice format questionnaire created to elicit students’ beliefs about autonomy. The results showed that learners consider learning to be a shared process in terms of responsibility. Nevertheless, conventional tasks are still observed as a responsibility for teachers. Results also showed that learners considered themselves to be able and felt willing to make decisions concerning planning, motivation and evaluation

Collective action in ant control:

Leaf-cutting ants (Atta. cephalotes) represents a serious problem to farmers in many parts of Latin America and accounts of ants eating up a whole cassava plot or destroying one or more fruit trees overnight are not uncommon. Ants do not respect farm boundaries. Therefore, farmers who control anthills on their own fields might still face damage on their crops caused by ants coming from neighboring fields where no control measures are taken. In that sense, crop damage caused by leaf-cutting ants constitutes a transboundary natural resource management problem which, in addition to technical interventions, requires organizational interventions to ensure a coordinated effort among farmers to be solved. This paper reports on a research effort initiated by CIAT and implemented jointly between CIAT and farmers in La Laguna - a small community in the Andean Hillsides of Southwestern Colombia. The objective of the research effort was two-fold: i) to identify low cost technical options for ant control, and ii) to analyze and visualize the transboundary nature of the ant control problem and thus identify organizational options to enable collective or coordinated ant control.

Biorefinery concept in the meat industry: From slaughterhouse biowastes to superaborbent materials

The expansion of food production has a large environmental impact in many ways. More specifically, 30–40% of total food production is lost as wastes and/or by-products before it reaches the market. In this sense, blood is an inevitable by-product in the meat industry that typically consists of 3–5% of the total weight of the animal. The dry organic matter present in blood is mostly protein, which can be employed more efficiently as raw material in the development of biodegradable materials. In the present manuscript, the blood collected after slaughtering of Iberian pigs was centrifuged and the upper (i.e., plasma) and bottom (i.e., red cells) layers were separated. Three freeze-dried fractions were characterized and evaluated on terms of their potential in the field of bioplastics: whole blood, plasma and bottom layer. Albumin was detected clearly in the plasma fraction, while globulins in red cells. After their characterization samples were mixed thoroughly with glycerol and injection molded at 120 ◦C. Special applications may be proposed for every fraction (i.e., whole blood, plasma or red cells), as the materials displayed different properties depending on the raw material employed. Thus, plasma resulted in materials with a greater deformability and swelling capacity during immersion, resulting in superabsorbent materials when processed at milder conditions (80 ◦C)The authors acknowledge the projects PID2021-124294OB-C21 and PID2021-124294OB-C22 funded by MCIN/AEI/10.13039/ 501100011033/ and by “ERDF A way of making Europe” which sup- ported this study. K.C. and P.G. thank the Basque Government for BIOMAT funding (IT1658-22). The authors would like to thank the Spanish Ministerio de Universidades for the PhD grant PRE2019-089815 awarded to E. ´Alvarez-Castillo. The blood used was collected from a local slaughterhouse, Mataderos del Sur, S.A. Authors also would like to thank for kindly supplying the raw material employed in the study. The authors also acknowledge to the Microanalysis and Microscopy services from CITIUS (Universidad de Sevilla) for providing full access and assistance to equipment used

Seed Dispersal Spectrum of Woody Species in South Ecuadorian Dry Forests: Environmental Correlates and the Effect of Considering Species Abundance

This study examines the seed dispersal spectrum of the tropical dry forests of Southern Ecuador, in an effort to contribute to the knowledge of the complex dynamics of tropical dry forests. Seed dispersal spectrum was described for a total number of 160 species. Relationships of dispersal syndromes with plant growth form and climatic seasonality were explored. For a subset of 97 species, we determined whether dispersal spectrum changes when species abundance, in addition to species number, is taken into account. The same subset was used to relate dispersal syndromes with the environmental conditions. Zoochorous species dominated in the studied community. When considering the individual abundance of each species, however, anemochory was the prevalent dispersal syndrome. We found a significant difference in the frequency of dispersal syndromes among plant growth forms, with epizoochory only occurring in shrub species. The dispersal spectrum was dependent on climatic seasonality. The largest proportion of anemochorous species fructified during the dry season, while zoochorous diaspores dominated during the rainy season. A fourth-corner analysis indicated that the seed dispersal spectrum of Southern Ecuador dry forests is controlled by environmental conditions such as annual precipitation, annual temperature range or topography. Our results suggest that spatio-temporal changes in the environmental conditions may affect important ecological processes for dispersal. Thus, the predominance of one syndrome or another may depend on the spatial variation of environmental conditions

Erythropoietin as a protective factor in rat CNS cells receiving radiotherapy: An in vitro study

Objetivo. Investigar el efecto de la eritropoyetina en cultivos celulares de corteza cerebral de ratas cuando se administra radioterapia. Materiales y métodos. El estudio se desarrolla con la obtención de corteza cerebral de embriones de 17 días de preñez de ratas Wistar. Las células cultivadas después de 72 horas de la extracción de la corteza se dividieron en dos grupos, a uno de ellos se le administró eritropoyetina alfa a una concentración de 30 pM y el otro era el grupo control. A los dos grupos de células se les radió con 6 Gy mediante un aparato Phoenix. Tras la radioterapia permanecieron 24 horas en la incubadora antes de fijarlas. Las células fueron fijadas con formaldehído al 4%. A continuación, con la técnica de TUNEL, se valoró el número de células apoptóticas en los cultivos radiados. Resultados. Se observó un porcentaje de apoptosis del 25,22% del grupo de cultivo sin eritropoyetina, mientras que en el grupo de células radiadas con eritropoyetina fue del 15,5%. Las variables cuantitativas se analizaron mediante el test t de Student y el resultado de la comparación entre los dos grupos fue estadísticamente significativo (p < 0,0001). Conclusión. En nuestro modelo experimental in vitro se comprobó que la eritropoyetina es eficaz en la prevención de la apoptosis en células del sistema nervioso central de ratas por radiación. Esto abre nuevos campos para la investigación del efecto protector del sistema nerviosoAim. To investigate the effect of erythropoietin in cultured rat cerebral cortex cells receiving radiotherapy. Materials and methods. Cerebral cortex was taken from 17-day-old Wistar rat embryos and placed in culture. At 72 hours, the cultures were divided into two groups, one receiving 30 pM erythropoietin alpha and the other was the control group. Both groups received 6 Gy from a Phoenix apparatus and were incubated for another 24 hours before fixation in 4% formaldehyde. TUNEL technique was employed to calculate the number of apoptotic cells in the irradiated cultures. 206 www.neurologia.com Rev Neurol 2014; 58 (5): 199-206 A. Gómez-De la Riva, et al Results. Apoptosis affected 25.22% of the cells cultured without erythropoietin and 15.5% in the group receiving erithropoyetin. Student’s t-test was used to analyse quantitative variables and showed a significant difference in apoptosis between the two groups (p < 0.0001). Conclusion. Our in vitro experimental model demonstrated that erythropoietin effectively prevents apoptosis in irradiated rat SNC cells, opening new fields for investigation into protective agents for the nervous syste