Clathrin and AP1B: Key roles in basolateral trafficking through trans-endosomal routes

Research following introduction of the MDCK model system to study epithelial polarity (1978) led to an initial paradigm that posited independent roles of the trans Golgi network (TGN) and recycling endosomes (RE) in the generation of, respectively, biosynthetic and recycling routes of plasma membrane (PM) proteins to apical and basolateral PM domains. This model dominated the field for 20 years. However, studies over the past decade and the discovery of the involvement of clathrin and clathrin adaptors in protein trafficking to the basolateral PM has led to a new paradigm. TGN and RE are now believed to cooperate closely in both biosynthetic and recycling trafficking routes. Here, we critically review these recent advances and the questions that remain unanswered.     

基于物质流分析的废纸回收利用体系生态成本研究

废弃物回收利用在一定程度上对缓解资源和环境危机起到积极的作用,已经成为可持续发展的重要举措,但生产过程中消耗的资源、能源,排放的污染物同样也会对自然环境产生负面影响。为解决此问题,以废纸回收利用体系为例,基于物质流分析方法构建了生态成本核算模型,为废弃物回收利用体系优化提供基础。在对生态成本相关研究归纳总结的基础上,定义了生态成本的概念,界定了生态成本的研究内容,并分析基于物质流核算生态成本的可行性。生态成本是对生态负荷的价值化,主要分为资源耗减成本、污染产生和环境保护成本以及生态环境损害成本3部分。污染产生和环境保护成本可以通过将总成本按比例分配给正、负产品的方式求得,资源耗减成本和环境损害成本借助LIME方法核算,总生态成本是回收利用体系内部各项生态成本的总和。生态成本核算是评价生态负荷的重要手段,在废纸回收利用体系物质流动图的基础上,分析各生产流程生态成本的构成情况。提出的生态成本核算模型不仅适用于废纸回收利用体系,其他废弃物也同样适用。通过生态成本的核算,寻找到对生态环境影响较大的工序、流程,为废弃物回收利用体系经济与环境的双赢提供理论与实践指导。     

The metamicrobiome: key determinant of the homeostasis of nutrient recycling

The metamicrobiome is an integrated concept to study carbon and nutrient recycling in ecosystems. Decomposition of plant-derived matter by free-living microbes and fire – two key recycling pathways – are highly sensitive to global change. Mutualistic associations of microbes with plants and animals strongly reduce this sensitivity. By solving a fundamental allometric trade-off between metabolic and homeostatic capacity, these mutualisms enable continued recycling of plant matter where and when conditions are unfavourable for the free-living microbiome. A diverse metamicrobiome – where multiple plant- and animal-associated microbiomes complement the free-living microbiome – thus enhances homeostasis of ecosystem recycling rates in variable environments. Research into metamicrobiome structure and functioning in ecosystems is therefore important for progress towards understanding environmental change.     

Apical to basolateral transcytosis and apical recycling of immunoglobulin G in trophoblast-derived BeWo cells: effects of low temperature, nocodazole, and cytochalasin D

The murine neonatal Fc receptor, FcRn, carries out two functions: materno-fetal IgG delivery and maintenance of serum IgG homeostasis. During human pregnancy maternal IgG is transferred across placental syncytiotrophoblasts presumably by the human homolog of FcRn, hFcRn. Trophoblast-derived BeWo cells express hFcRn endogenously and can be considered as a model system to investigate IgG transport in syncytiotrophoblasts. Using a pulse-chase protocol, we here demonstrate that polarized BeWo cells exhibit not only apical to basolateral transcytosis but also apical IgG recycling. Thus, for the first time we demonstrate that epithelial cells can be involved in both materno-fetal IgG transmission and regulation of serum IgG levels. Lowering the temperature from 37 to 16 degrees C reduced, but did not block, IgG recycling and transcytosis. Microtubule-disruption by nocodazole did not influence transcytosis or apical recycling. Disassembly of filamentous actin by cytochalasin D stimulated apical endocytosis and recycling, while transcytosis remained unaffected. In summary, in BeWo cells apically internalized IgG enters both a transcytotic and recycling pathway. While the transcytotic route is temperature-sensitive but independent from microtubules and actin filaments, the apical recycling pathway is temperature-influenced and stimulated by actin disassembly, suggestive for the involvement of distinct endosome subcompartments in transcytosis and recycling.     

Global dynamics of a selection model for the growth of a population with genotypic fertility differences

A population growth model is considered for a one locus two allele problem with selection based entirely on fertility differences. A local stability analysis is carried out for the critical points — which include possible polymorphic states — of the resulting nonlinear differential equations. The methods of dynamical systems theory are applied to obtain limiting genotypic proportions for every initial state. Thus the results are global and there are no periodic solutions.Research for this paper was partially supported by the National Science and Engineering Research Council of Canada Grant NSERC A-8130Research for this paper was partially supported by the National Science and Engineering Research Council of Canada Grant NSERC A-4823Research supported by NSF Grant MCS 7901069. A portion of the work was carried out while the author was a Visiting Professor at the University of Utah, Salt Lake City, Utah     

Sequence-dependent sorting of recycling proteins by actin-stabilized endosomal microdomains

The functional consequences of signaling receptor endocytosis are determined by the endosomal sorting of receptors between degradation and recycling pathways. How receptors recycle efficiently, in a sequence-dependent manner that is distinct from bulk membrane recycling, is not known. Here, in live cells, we visualize the sorting of a prototypical sequence-dependent recycling receptor, the beta-2 adrenergic receptor, from bulk recycling proteins and the degrading delta-opioid receptor. Our results reveal a remarkable diversity in recycling routes at the level of individual endosomes, and indicate that sequence-dependent recycling is an active process mediated by distinct endosomal subdomains distinct from those mediating bulk recycling. We identify a specialized subset of tubular microdomains on endosomes, stabilized by a highly localized but dynamic actin machinery, that mediate this sorting, and provide evidence that these actin-stabilized domains provide the physical basis for a two-step kinetic and affinity-based model for protein sorting into the sequence-dependent recycling pathway.     

Recycling probability and dynamical properties of germinal center reactions

We introduce a new model for the dynamics of centroblasts and centrocytes in a germinal center. The model reduces the germinal center reaction to the elements considered as essential and embeds proliferation of centroblasts, point mutations of the corresponding antibody types represented in a shape space, differentiation to centrocytes, selection with respect to initial antigens, differentiation of positively selected centrocytes to plasma or memory cells and recycling of centrocytes to centroblasts. We use exclusively parameters with a direct biological interpretation such that, once determined by experimental data, the model gains predictive power. Based on the experiment of Han et al. (1995b) we predict that a high rate of recycling of centrocytes to centroblasts is necessary for the germinal center reaction to work reliably. Furthermore, we find a delayed start of the production of plasma and memory cells with respect to the start of point mutations, which turns out to be necessary for the optimization process during the germinal center reaction. The dependence of the germinal center reaction on the recycling probability is analysed.     

荷兰废弃混凝土回收利用产业发展借鉴

荷兰对建筑废弃物尤其是废弃混凝土的回收利用处于国际领先水平。对荷兰废弃混凝土回收利用产业的利益相关者行为和相互关系进行分析,基于波特钻石模型理清荷兰废弃混凝土回收利用产业发展机制。借鉴荷兰发展的经验,结合国情提出促进我国混凝土回收利用产业发展的建议。     

Toward Estimating Displaced Primary Production from Recycling: A Case Study of U.S. Aluminum

Recycling materials from end‐of‐life products has the potential to create environmental benefit by displacing more harmful primary material production. However, displacement is governed by market forces and is not guaranteed; if full displacement does not occur, the environmental benefits of recycling are reduced or eliminated. Therefore, quantifying the true “displacement rate” caused by recycling is essential to accurately assess environmental benefits and make optimal environmental management decisions. Our 2016 article proposed a market‐based methodology to estimate actual displacement rates following an increase in recycling or reuse. The current article demonstrates the operation, utility, and challenges of that methodology in the context of the U.S. aluminum industry. Sensitivity analyses reveal that displacement estimates are sensitive to uncertainty in price elasticities. Results suggest that 100% displacement is unlikely immediately following a sustained supply‐driven increase in aluminum recycling and even less likely in the long term. However, zero and even negative displacement are possible. A variant of the model revealed that demand‐driven increases in recycling are less likely than supply‐driven changes to result in full displacement. However, model limitations exist and challenges arose in the estimation process, the effects of which are discussed. We suggest implications for environmental assessment, present lessons learned from applying the estimation methodology, and highlight the need for further research in the market dynamics of recycling.     

Persistence and coexistence in zooplankton-phytoplankton-nutrient models with instantaneous nutrient recycling

We consider plankton-nutrient interaction models consisting of phytoplankton, herbivorous zooplankton and dissolved limiting nutrient with general nutrient uptake functions and instantaneous nutrient recycling. For the model with constant nutrient input and different constant washout rates, conditions for boundedness of the solutions, existence and stability of non-negative equilibria, as well as persistence are given. We also consider the zooplankton-phytoplankton-nutrient interaction models with a fluctuating nutrient input and with a periodic washout rate, respectively. It is shown that coexistence of the zooplankton and phytoplankton may arise due to positive bifurcating periodic solutions.Research has been supported in part by a University of Alberta Ph.D. Scholarship and is in part based on the author's Ph.D. thesis under the supervision of Professor H. 1. Freedman, to whom the author owes a debt of appreciation and gratitude for his kind advice, helpful comments and continuous encouragement     

Re-evaluating the recycling hypothesis in the germinal centre

Mathematical models have been used to study different aspects of the germinal centre reaction, in particular, affinity maturation of antibodies and the hypothesis of recycling. So far, interpretation of several theoretical and experimental results has pointed to the existence of recycling. However, theoretical models have seldom been compared with experimental data from specific immune responses and the potential relevance of recycling in the germinal centre is still an open problem. In this article, we propose a model without recycling that takes into account selection mechanisms that were previously uncovered experimentally. We apply the model to several experimental systems that use different Ag and compare the results with experimental data of affinity maturation whenever available. The results obtained for a primary immune response to the hapten (4-hydroxy-3-nitrophenyl)-acetyl show that recycling is not a necessary mechanism to achieve the level of affinity maturation observed in germinal centre reactions. Similar levels of affinity maturation are obtained for other responses, although for antibodies involving several affinity-enhancing mutations the affinity maturation obtained with the model is much lower. Interpretation of these results and consequences towards the concept of recycling are discussed.     

Analysis of coated pit recycling on human fibroblasts

The recycling to the cell surface of previously internalized coated pits has been proposed as a likely mechanism for the rapid regeneration of coated pits on human fibroblast surfaces at 37 degrees C (1). We present a general mathematical model of coated pit recycling for the case when the coat cycles as a single unit, and use it to analyze certain time and temperature dependent data obtained by Anderson et al. (1) and Vermeer et al. (2). We show how recycling can account for these data and how this type of data can be used to distinguish between different possible recycling mechanisms. We show that these data are inconsistent with a two compartment model where coat material simply shuttles back and forth between coated pits and short-lived coated vesicles. From these data we estimate for human fibroblasts at 37 degrees C: that the time for a coated pit to be replenished through recycling after it is lost through internalization is greater than 3.5 min; and that at any moment 53% or less of the cell's clathrin that is involved in coated pit recycling is on the cell surface.     

Caenorhabditis elegans num-1 negatively regulates endocytic recycling

Much of the material taken into cells by endocytosis is rapidly returned to the plasma membrane by the endocytic recycling pathway. Although recycling is vital for the correct localization of cell membrane receptors and lipids, the molecular mechanisms that regulate recycling are only partially understood. Here we show that in Caenorhabditis elegans endocytic recycling is inhibited by NUM-1A, the nematode Numb homolog. NUM-1AGFP fusion protein is localized to the baso-lateral surfaces of many polarized epithelial cells, including the hypodermis and the intestine. We show that increased NUM-1A levels cause morphological defects in these cells similar to those caused by loss-of-function mutations in rme-1, a positive regulator of recycling in both C. elegans and mammals. We describe the isolation of worms lacking num-1A activity and show that, consistent with a model in which NUM-1A negatively regulates recycling in the intestine, loss of num-1A function bypasses the requirement for RME-1. Genetic epistasis analysis with rab-10, which is required at an early part of the recycling pathway, suggests that loss of num-1A function does not affect the uptake of material by endocytosis but rather inhibits baso-lateral recycling downstream of rab-10.     

Molecular aspects of nitrogen mobilization and recycling in trees

Plants have developed a variety of molecular strategies to use limiting nutrients with a maximum efficiency. N assimilated into biomolecules can be released in the form of ammonium by plant metabolic activities in various physiological processes such as photorespiration, the biosynthesis of phenylpropanoids or the mobilization of stored reserves. Thus, efficient reassimilation mechanisms are required to reincorporate liberated ammonium into metabolism and maintain N plant economy. Although the biochemistry and molecular biology of ammonium recycling in annual herbaceous plants has been previously reported, the recent advances in woody plants need to be reviewed. Moreover, it is important to point out that N recycling is quantitatively massive during some of these metabolic processes in trees, including seed germination, the onset of dormancy and resumption of active growth or the biosynthesis of lignin that takes place during wood formation. Therefore, woody plants constitute an excellent system as a model to study N mobilization and recycling. The aim of this paper is to provide an overview of different physiological processes in woody perennials that challenge the overall plant N economy by releasing important amounts of inorganic N in the form of ammonium.     

Asymmetric Rab 11 endosomes regulate delta recycling and specify cell fate in the Drosophila nervous system

Drosophila sensory organ precursor (SOP) cells are a well-studied model system for asymmetric cell division. During SOP division, the determinants Numb and Neuralized segregate into the pIIb daughter cell and establish a distinct cell fate by regulating Notch/Delta signaling. Here, we describe a Numb- and Neuralized-independent mechanism that acts redundantly in cell-fate specification. We show that trafficking of the Notch ligand Delta is different in the two daughter cells. In pIIb, Delta passes through the recycling endosome which is marked by Rab 11. In pIIa, however, the recycling endosome does not form because the centrosome fails to recruit Nuclear fallout, a Rab 11 binding partner that is essential for recycling endosome formation. Using a mammalian cell culture system, we demonstrate that recycling endosomes are essential for Delta activity. Our results suggest that cells can regulate signaling pathways and influence their developmental fate by inhibiting the formation of individual endocytic compartments.     

Stoichiometry, herbivory and competition for nutrients: simple models based on planktonic ecosystems

Models are examined in which two prey species compete for two nutrient resources, and are preyed upon by a predator that recycles both nutrients. Two factors determine the effective relative supply of the nutrients, hence competitive outcomes: the external nutrient supply ratio, and the relative recycling of the two nutrients within the system. This second factor is governed by predator stoichiometry--its relative requirements for nutrients in its own biomass. A model with nutrient resources that are essential for the competing prey is detailed. Criteria are given to identify the limiting nutrient for a food chain of one competitor with the predator. Increased supply of this limiting nutrient increases predator density and concentration of this nutrient at equilibrium, while decreasing the concentration of a non-limiting nutrient. Changes in supply or recycling of a non-limiting nutrient affect only the concentration of that nutrient. Criteria for the invasion of a second prey competitor are presented. When different nutrients limit growth of the resident prey and the invader, increased supply or recycling of the invader's limiting nutrient assists invasion, while increased supply or recycling of the resident's limiting nutrient hinders invasion. If the same nutrient limits both resident and invader, then changes in supply and recycling have complex effects on invasion, depending on species properties. In a parameterized model of a planktonic ecosystem, green algae and cyanobacteria coexist over a wide range of nitrogen:phosphorus supply ratios, without predators. When the herbivore Daphnia is added, coexistence is eliminated or greatly restricted, and green algae dominate over a wide range of supply conditions, because the effective supply of P is greatly reduced as Daphnia rapidly recycles N.     

Analysis of coated pit recycling on human fibroblasts

The recycling to the cell surface of previously internalized coated pits has been proposed as a likely mechanism for the rapid regeneration of coated pits on human fibroblast surfaces at 37°C (1). We present a general mathematical model of coated pit recycling for the case when the coat cycles as a single unit, and use it to analyze certain time and temperature dependent data obtained by Anderson et al. (1) and Vermeer et al. (2). We show how recycling can account for these data and how this type of data can be used to distinguish between different possible recycling mechanisms. We show that these data are inconsistent with a two compartment model where coat material simply shuttles back and forth between coated pits and short-lived coated vesicles. From these data we estimate for human fibroblasts at 37°C: that the time for a coated pit to be replenished through recycling after it is lost through internalization is greater than 3.5 min; and that at any moment 53% or less of the cell’s clathrin that is involved in coated pit recycling is on the cell surface.     

A Material Flow‐based Approach to Enhance Resource Efficiency in Production and Recycling Networks

Resource and energy efficiency are key strategies for production and recycling networks. They can contribute to more sustainable industrial production and can help cope with challenges such as competition, rising resource and energy prices, greenhouse gas emissions reduction, and scarce and expensive landfill space. In pursuit of these objectives, further enhancements of single processes are often technologically sophisticated and expensive due to past achievements that have brought the processes closer to technical optima. Nevertheless, the potential for network‐wide advancements may exist. Methods are required to identify and assess the potential for promising resource and energy efficiency measures from technical, economic, and ecological perspectives. This article presents an approach for a material flow‐based techno‐economic as well as ecological analysis and assessment of resource efficiency measures in production and recycling networks. Based on thermodynamic process models of different production and recycling processes, a material and energy flow model of interlinked production and recycling processes on the level of chemical compounds is developed. The model can be used to improve network‐wide resource efficiency by analyzing and assessing measures in scenario and sensitivity analyses. A necessary condition for overcoming technical and economic barriers for implementing such measures can be fulfilled by identifying strategies that appear technologically feasible and economically and ecologically favorable. An exemplary application to a production and recycling network of the German steel and zinc industry is presented. From a methodological point of view, the approach shows one way of introducing thermodynamics and further technological aspects into industrial planning and assessment.     

The Nonlinear Relationship between Paper Recycling and Primary Pulp Requirements

Waste paper is suitable for recycling back into paper or for incineration for energy recovery. If waste paper is used for recycling, secondary pulp replaces virgin pulp. Fiber recycling is limited, however, because of physical constraints—particularly the breakage of fiber in the recycling process—and a permanent input of virgin fiber to the system is required. Therefore one can expect that the relationship between recycling rates and resource requirements is represented by a curved line rather than a straight one. In this article, we present a mathematical model which confirms that the relationship between recycling rates and primary pulp requirements can be described as nonlinear. Furthermore, we show that this nonlinear relationship leads to an optimal recycling rate with regard to energy consumption: 93 persent for paper produced from chemical pulp, and 81 persent for paper produced from mechanical pulp. Sensitivity testing additionally reveals that at low recycling rates increasing waste paper recycling is energy efficient, but it becomes less efficient at higher recycling rates. Close to the optimum recycling rates (within 10 persent), increasing or decreasing the rate affects the total energy requirement less than 0.3%     

Myosin Vb is required for trafficking of the cystic fibrosis transmembrane conductance regulator in Rab11a-specific apical recycling endosomes in polarized human airway epithelial cells

Cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl(-) secretion across fluid-transporting epithelia is regulated, in part, by modulating the number of CFTR Cl(-) channels in the plasma membrane by adjusting CFTR endocytosis and recycling. However, the mechanisms that regulate CFTR recycling in airway epithelial cells remain unknown, at least in part, because the recycling itineraries of CFTR in these cells are incompletely understood. In a previous study, we demonstrated that CFTR undergoes trafficking in Rab11a-specific apical recycling endosomes in human airway epithelial cells. Myosin Vb is a plus-end-directed, actin-based mechanoenzyme that facilitates protein trafficking in Rab11a-specific recycling vesicles in several cell model systems. There are no published studies examining the role of myosin Vb in airway epithelial cells. Thus, the goal of this study was to determine whether myosin Vb facilitates CFTR recycling in polarized human airway epithelial cells. Endogenous CFTR formed a complex with endogenous myosin Vb and Rab11a. Silencing myosin Vb by RNA-mediated interference decreased the expression of wild-type CFTR and DeltaF508-CFTR in the apical membrane and decreased CFTR-mediated Cl(-) secretion across polarized human airway epithelial cells. A recombinant tail domain fragment of myosin Vb attenuated the plasma membrane expression of CFTR by arresting CFTR recycling. The dominant-negative effect was dependent on the ability of the myosin Vb tail fragment to interact with Rab11a. Taken together, these data indicate that myosin Vb is required for CFTR recycling in Rab11a-specific apical recycling endosomes in polarized human airway epithelial cells.