Development of Morphogen Gradient: The Role of Dimension and Discreteness

The fundamental processes of biological development are governed by multiple signaling molecules that create non-uniform concentration profiles known as morphogen gradients. It is widely believed that the establishment of morphogen gradients is a result of complex processes that involve diffusion and degradation of locally produced signaling molecules. We developed a multi-dimensional discrete-state stochastic approach for investigating the corresponding reaction-diffusion models. It provided a full analytical description for stationary profiles and for important dynamic properties such as local accumulation times, variances and mean first-passage times. The role of discreteness in developing of morphogen gradients is analyzed by comparing with available continuum descriptions. It is found that the continuum models prediction about multiple time scales near the source region in two-dimensional and three-dimensional systems is not supported in our analysis. Using ideas that view the degradation process as an effective potential, the effect of dimensionality on establishment of morphogen gradients is also discussed. In addition, we investigated how these reaction-diffusion processes are modified with changing the size of the source region

Theoretical Analysis of Dynamic Processes for Interacting Molecular Motors

Biological transport is supported by collective dynamics of enzymatic molecules that are called motor proteins or molecular motors. Experiments suggest that motor proteins interact locally via short-range potentials. We investigate the fundamental role of these interactions by analyzing a new class of totally asymmetric exclusion processes where interactions are accounted for in a thermodynamically consistent fashion. Theoretical analysis that combines various mean-field cal- culations and computer simulations suggests that dynamic properties of molecular motors strongly depend on interactions, and correlations are stronger for interacting motor proteins. Surprisingly, it is found that there is an optimal strength of interactions (weak repulsion) that leads to a maxi- mal particle flux. It is also argued that molecular motors transport is more sensitive to attractive interactions. Applications of these results for kinesin motor proteins are discussed

Theoretical analysis of degradation mechanisms in the formation of morphogen gradients

Fundamental biological processes of development of tissues and organs in multicellular organisms are governed by various signaling molecules, which are called morphogens. It is known that spatial and temporal variations in the concentration profiles of signaling molecules, which are frequently referred as morphogen gradients, lead to a cell differentiation via activating specific genes in a concentration-dependent manner. It is widely accepted that the establishment of the morphogen gradients involves multiple biochemical reactions and diffusion processes. One of the critical elements in the formation of morphogen gradients is a degradation of signaling molecules. We develop a new theoretical approach that provides a comprehensive description of the degradation mechanisms. It is based on the idea that the degradation works as an effective potential that drives the signaling molecules away from the source region. Utilizing the method of first-passage processes, the dynamics of the formation of morphogen gradients for various degradation mechanisms is explicitly evaluated. It is found that linear degradation processes lead to a dynamic behavior specified by times to form the morphogen gradients that depend linearly on the distance from the source. This is because the effective potential due to the degradation is quite strong. At the same time, nonlinear degradation mechanisms yield a quadratic scaling in the morphogen gradients formation times since the effective potentials are much weaker. Physical-chemical explanations of these phenomena are presented

Effects of sesame meal on intake, digestibility, rumen characteristics, chewing activity and growth of lambs

Two experiments were carried out to determine ruminal degradability of sesame meal (SSM) and its effects on intake, digestibility, rumen parameters, chewing activity, and lamb performance when it replaced soybean meal (SBM). Degradability of dry matter (DM) and crude protein (CP) were determined with the nylon bag technique using three fistulated Zel ewes. The quickly and potentially degradable DM of SSM was lower, but their degradation rates of DM were similar. The quickly degradable protein in the SSM was greater, but the slowly degradable protein of SSM was lower. Potential degradable protein of SBM was greater. The degradation rate of protein was greater in the SSM. Thirty Zel lambs were assigned to five treatments, namely 1) control diet that contained SBM, and 2), 3), 4) and 5) diets that contained 25, 50, 75, and 100% DM of SSM partially or entirely replacing SBM and part of barley grain. There was no difference in the intakes of DM, CP, ether extract (EE), and non-fibre carbohydrate (NFC) among treatments, but neutral detergent fibre (NDF) intake increased when the SSM inclusion rate was increased. Digestibility of DM and EE, passage rate, and total mean retention time differed, but the digestibility of NDF, CP, and NFC, rumen liquid pH and NH3-N, passage rate, rumen retention time, eating time, rumination, total chewing activity, DM intake, daily gain, feed conversation ratio, carcass yield and characteristics were not different between treatments. Replacing the SBM with SSM in lamb, improved intake, digestibility, and rumen condition, without reduction in performance and carcass composition.Keywords: Carcass characteristic, feedlotting, lamb, mean retention time, ruminal degradability, soybean mea

All-time dynamics of continuous-time random walks on complex networks

The concept of continuous-time random walks (CTRW) is a generalization of ordinary random walk models, and it is a powerful tool for investigating a broad spectrum of phenomena in natural, engineering, social, and economic sciences. Recently, several theoretical approaches have been developed that allowed to analyze explicitly dynamics of CTRW at all times, which is critically important for understanding mechanisms of underlying phenomena. However, theoretical analysis has been done mostly for systems with a simple geometry. Here we extend the original method based on generalized master equations to analyze all-time dynamics of CTRWmodels on complex networks. Specific calculations are performed for models on lattices with branches and for models on coupled parallelchain lattices. Exact expressions for velocities and dispersions are obtained. Generalized fluctuations theorems for CTRW models on complex networks are discussed

Comparison of the effect of letrozole alone with letrozole plus n-acetylcysteine on pregnancy rate in patients with polycystic ovarian syndrome: A randomized clinical trial

Objectives: Different drugs are prescribed for the induction of ovulation in patients with polycystic ovary syndrome (PCOS). The aim of this study was to compare the effect of letrozole alone with letrozole plus N-acetyl cysteine (NAC) on the pregnancy rate in patients with PCOS. Materials and Methods: This clinical trial studyincluded317 patients with PCOS in the infertility clinic of Zahedan in 2018. Patients were randomly divided into letrozole and NAC plus letrozole groups. Then, several parameters were evaluated in both groups, including the pregnancy rate, number of follicles larger than 18 mm, endometrial thickness, and the endometrial pattern. Finally, data were analyzed using SPSS 25, and t-test and chi-square tests were used for statistical analysis. Results: The mean age of study participants was 28.5 ± 4.9 years old. The mean duration of infertility in the intervention group was 4.5 ± 3.8 years. The mean anti-Müllerian hormone and the mean endometrial thickness of patients in the intervention group were 4.4± 3.6 ng/mL and 7.6 ± 2.5 mm, respectively. Eventually, the pregnancy rate was 14.6 (n = 23) and 7.5 (n = 12) in the intervention and control groups, respectively (P = 0.046). Conclusions: The results of this search revealed that the number of follicles with the size of 18 mm in the control group was higher compared to the intervention group, but the fertility rate in patients with PCOS receiving letrozole plus N-acetylcysteine was significantly higher. © 2021 The Author(s);

A model of online protection to reduce children's online risk exposure: empirical evidence from Asia

Children are surrounded by a variety of digital media and are exposed to potential risks that come with such easy accessibility. Learning how to be safe online is an important consideration for both children and their caregivers. The present study proposes an integrated model of online safety based on constructs from protection motivation theory and the health belief model, namely perceived severity of (and susceptibility to) risk, online self-efficacy, online privacy concern, and digital literacy. The study comprised a survey conducted among 420 schoolchildren aged 9–16 years. Using partial least squares-structural equation modelling, the results illustrated the presence of a negative effect of ‘perceived severity of online risk’ toward online risks, whereas the effect of ‘digital literacy’ was found to be positive. Children whose perception of online risks was more severe were less exposed to online risks if they had higher ‘online privacy concerns’ than the children with higher ‘digital literacy’ who are more exposed to online risk. Results of the study show that engaging in safe online behaviour requires children to have a high perception regarding severity of online risks as well as knowledge of online privacy concerns. Online risks and opportunities occur in parallel. Consequently, the factors that increase or decrease risk may also increase or decrease the benefits