Telomerase: Structure,functions, and activity regulation

Telomerase is the enzyme responsible for maintenance of the length of telomeres by addition of guanine-rich repetitive sequences. Telomerase activity is exhibited in gametes and stem and tumor cells. In human somatic cells proliferation potential is strictly limited and senescence follows approximately 50–70 cell divisions. In most tumor cells, on the contrary, replication potential is unlimited. The key role in this process of the system of the telomere length maintenance with involvement of telomerase is still poorly studied. No doubt, DNA polymerase is not capable to completely copy DNA at the very ends of chromosomes; therefore, approximately 50 nucleotides are lost during each cell cycle, which results in gradual telomere length shortening. Critically short telomeres cause senescence, following crisis, and cell death. However, in tumor cells the system of telomere length maintenance is activated. Besides catalytic telomere elongation, independent telomerase functions can be also involved in cell cycle regulation. Inhibition of the telomerase catalytic function and resulting cessation of telomere length maintenance will help in restriction of tumor cell replication potential. On the other hand, formation of temporarily active enzyme via its intracellular activation or due to stimulation of expression of telomerase components will result in telomerase activation and telomere elongation that can be used for correction of degenerative changes. Data on telomerase structure and function are summarized in this review, and they are compared for evolutionarily remote organisms. Problems of telomerase activity measurement and modulation by enzyme inhibitors or activators are considered as well.     

中国多孔菌多样性初探:物种、区系和生态功能

多孔菌是指子实层体呈孔状且质地为革质至木质的一类大型担子菌,主要生长在各类木材上。我国地域辽阔,气候带和地形多样,森林类型和植被组成丰富,为多孔菌提供了丰富的栖息地。长期的野外资源调查和标本采集,特别是近年来分子生物学技术的发展,极大地丰富了对我国多孔菌种类的认识。我国是世界上多孔菌物种多样性最丰富的国家,现在已知有多孔菌704种,隶属于11目22科134属,包括世界广布成分、北温带成分和热带-亚热带成分。多孔菌中的白腐菌是潜在的工业用菌,褐腐菌在森林的更新过程中起重要作用。     

Rap1 GTPase: functions, regulation, and malignancy

Rap1 is a member of the Ras family of small GTPases that is activated by diverse extracellular stimuli in many cell types. It is activated by distinct types of Rap1 guanine nucleotide exchange factors coupled with various receptors or second messengers, while activated Rap1 is down-regulated by Rap1 GTPase-activating proteins, through which Rap1 activation is controlled spatio-temporally. Functionally, Rap1 either interferes with Ras-mediated ERK activation or activates ERK independently of Ras in a cell-context dependent manner. Accumulating evidence also indicates that Rap1 is a major activator of integrins, playing important roles in the regulation of a variety of integrin-dependent cellular functions. Most recently, significant evidence has emerged that dysregulation of Rap1 activation is responsible for the development of malignancy. Recent extensive research has begun to unveil the roles of this controversial small G protein in physiology and diseases.     

The PINCH-ILK-parvin complexes: assembly, functions and regulation

Cell-extracellular matrix (ECM) adhesion is mediated by transmembrane cell adhesion receptors (e.g., integrins) and receptor proximal cytoplasmic proteins. Over the past several years, studies using biochemical, structural, cell biological and genetic approaches have provided important evidence suggesting crucial roles of integrin-linked kinase (ILK), PINCH and CH-ILKBP/actopaxin/affixin/parvin (abbreviated as parvin herein) in ECM control of cell behavior. One general theme emerging from these studies is that the formation of ternary protein complexes consisting of ILK, PINCH and parvin is pivotal to the functions of PINCH, ILK and parvin proteins. In addition, recent studies have begun to uncover the molecular mechanisms underlying the assembly, functions and regulation of the PINCH-ILK-parvin (PIP) complexes. The PIP complexes provide crucial physical linkages between integrins and the actin cytoskeleton and transduce diverse signals from ECM to intracellular effectors. Among the challenges of future studies are to define the functions of different PIP complexes in various cellular processes, identify additional partners of the PIP complexes that regulate and/or mediate the functions of the PIP complexes, and determine the roles of the PIP complexes in the pathogenesis of human diseases involving abnormal cell-ECM adhesion and signaling.     

Atypical mitogen-activated protein kinases: structure, regulation and functions

Mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that play a central role in transducing extracellular cues into a variety of intracellular responses ranging from lineage specification to cell division and adaptation. Fourteen MAP kinase genes have been identified in the human genome, which define 7 distinct MAP kinase signaling pathways. MAP kinases can be classified into conventional or atypical enzymes, based on their ability to get phosphorylated and activated by members of the MAP kinase kinase (MAPKK)/MEK family. Conventional MAP kinases comprise ERK1/ERK2, p38s, JNKs, and ERK5, which are all substrates of MAPKKs. Atypical MAP kinases include ERK3/ERK4, NLK and ERK7. Much less is known about the regulation, substrate specificity and physiological functions of atypical MAP kinases.     

Brain insulin: regulation,mechanisms of action and functions

1. While many questions remain unanswered, it is now well documented that, contrary to earlier views, insulin is an important neuromodulator, contributing to neurobiological processes, in particular energy homeostasis and cognition. A specific role on cognitive functions related to feeding is proposed, and it is suggested that brain insulin from different sources might be involved in the above vital functions in health and disease.2. A molecule identical to pancreatic insulin, and specific insulin receptors, are found widely distributed in the central nervous system networks related to feeding, reproduction, or cognition.3. The actions of insulin in the central nervous system may be under both multilevel and multifactorial controls. The amount of blood insulin reaching the brain, brain insulin stores and secretion, potential local biosynthesis and degradation of the peptide, and insulin receptors and signal transduction can be affected by metabolic factors induced by nutrients, hormones, neurotransmitters, and regulatory peptides, peripherally or in the central nervous system.4. Glucose and serotonin regulate insulin directly in the hypothalamus and may be of importance for its biological effects. Central mechanisms regulating glucose-induced insulin secretion show some analogy with the mechanisms operating in the pancreas.5. A cross-talk between insulin and leptin receptors has been observed in the brain, and a regulation of central insulin actions, potentially via serotonin modulation, by leptin, galanin, melanocortins, and neuropeptide Y (NPY) is suggested.6. A more complete knowledge of the biological role of insulin in brain function and dysfunction, and of the regulatory mechanisms involved in these processes, constitutes a real advancement in the understanding of the pathophysiology of metabolic and mental diseases and could lead to important medical benefits.     

Nectar: properties, floral aspects, and speculations on origin

Although nectar is crucial for most pollinators, its evolutionary origin has received scant attention. Nectar is derived from the phloem solution. Both have high sugar concentrations (usually 10-30% solutes by fresh mass); the main solute in the phloem is sucrose, whereas nectar can also contain considerable amounts of fructose and glucose. The phloem, not the xylem, is the supplier of water to flowers and certain other organs. Therefore, a 'leaky phloem' hypothesis for the origin of nectar is presented based on the elevated hydrostatic pressure that can occur within the phloem and the structural weakness of developing phloem tissues. A 'sugar excretion' hypothesis is also presented that considers the solute accumulation resulting from the relatively high transpiration rates of flowers.     

Evolution of pesticide resistance: interactions between generation time and genetic, ecological, and operational factors

We used computer simulation modeling to clarify the relationship between generation time and the rate of evolution of pesticide resistance. We examined the influence of generation time under various assumptions about genetics, population dynamics and selection pressures. The simplest model demonstrated that the time required for resistance to evolve can be independent of generation time. However, interactions of generation time with genetic, biological and operational factors resulted in positive, negative, and U-shaped relationships between the number of generations per year and the time required for resistance to evolve. These results preclude any generalizations concerning the influence of generation time on resistance evolution. Some ability to predict the influence of generation time may still exist on a case-by-case basis if the context of the resistance episode can be specified.     

Special issue: Urban green infrastructure and the ecological functions

Landscape and Ecological Engineering -     

Plant aquaporins: novel functions and regulation properties

Aquaporins are water channel proteins of intracellular and plasma membranes that play a crucial role in plant water relations. The present review focuses on the most recent findings concerning the molecular and cellular properties of plant aquaporins. The mechanisms of transport selectivity and gating (i.e. pore opening and closing) have recently been described, based on aquaporin structures at atomic resolution. Novel dynamic aspects of aquaporin subcellular localisation have been uncovered. Also, some aquaporin isoforms can transport, besides water, physiologically important molecules such as CO(2), H(2)O(2), boron or silicon. Thus, aquaporins are involved in many great functions of plants, including nutrient acquisition, carbon fixation, cell signalling and stress responses.     

Extracellular TG2: emerging functions and regulation

Tissue transglutaminase (TG2) is a ubiquitously expressed member of the transglutaminase family of Ca(2+)-dependent crosslinking enzymes. Unlike other family members, TG2 is a multifunctional protein, which has several other well documented enzymatic and non-enzymatic functions. A significant body of evidence accumulated over the last decade reveals multiple and complex activities of this protein on the cell surface and in the extracellular matrix (ECM), including its role in the regulation of cell-ECM interactions and outside-in signaling by several types of transmembrane receptors. Moreover, recent findings indicate a dynamic regulation of the levels and functions of extracellular TG2 by several complementary mechanisms. This review summarizes and assesses recent research into the emerging functions and regulation of extracellular TG2.     

Complementarity of ecological goal functions

This paper summarizes, in the framework of network environ analysis, a set of analyses of energy-matter flow and storage in steady-state systems. The network perspective is used to codify and unify ten ecological orientors or extremal principles: maximum power (Lotka), maximum storage (J?rgensen-Mejer), maximum empower and emergy (Odum), maximum ascendency (Ulanowicz), maximum dissipation (Schneider-Kay), maximum cycling (Morowitz), maximum residence time (Cheslak-Lamarra), minimum specific dissipation (Onsager, Prigogine), and minimum empower to exergy ratio (Bastianoni-Marchettini). We show that, seen in this framework, these seemingly disparate extrema are all mutually consistent, suggesting a common pattern for ecosystem development. This pattern unfolds in the network organization of systems.     

Myosin light chain kinase MYLK1: Anatomy,interactions, functions,and regulation

This review discusses and summarizes the results of molecular and cellular investigations of myosin light chain kinase (MLCK, MYLK1), the key regulator of cell motility. The structure and regulation of a complex mylk1 gene and the domain organization of its products is presented. The interactions of the mylk1 gene protein products with other proteins and posttranslational modifications of the mylk1 gene protein products are reviewed, which altogether might determine the role and place of MLCK in physiological and pathological reactions of cells and entire organisms. Translational potential of MLCK as a drug target is evaluated.     

Biosynthesis,regulation and functions of tocochromanols in plants

Tocopherols and tocotrienols have been originally identified as essential nutrients in mammals based on their vitamin E activity. These lipid-soluble compounds are potent antioxidants that protect polyunsaturated fatty acids from lipid peroxidation. The biosynthesis of tocopherols and tocotrienols occurs exclusively in photosynthetic organisms. The biosynthetic precursors and the different pathway intermediates have been identified by biochemical studies and the different vitamin E biosynthetic genes (VTE genes) have been isolated in several plants and cyanobacteria. The characterization of transgenic plants overexpressing one or multiple VTE genes combined with the study of vitamin E deficient mutants allows from now on understanding the regulation and the function of tocopherols and tocotrienols in plants.     

ATP-dependent potassium channels of muscle cells: Their properties,regulation, and possible functions

ATP-dependent potassium channels are present at high density in the membranes of heart, skeletal, and smooth muscle and have a lowP _open at physiological [ATP]_i. The unitary conductance is 15–20 pS at physiological [K⁺] _o , and the channels are highly selective for K⁺. Certain sulfonylureas are specific blockers, and some K channel openers may also act through these channels. K_ATP channels are probably regulated through the binding of ATP, which may in turn be regulated through changes in the ADP/ATP ratio or in pH_i. There is some evidence for control through G-proteins. The channels have complex kinetics, with multiple open and closed states. The main effect of ATP is to increase occupancy of long-lived closed states. The channels may have a role in the control of excitability and probably act as a route for K⁺ loss from muscle during activity. In arterial smooth muscle they may act as targets for vasodilators.