Dynamic function and regulation of apoplast in the plant body

Apoplast is the internal environment of plant. Our body posses the internal environment that consists of blood, lympha, and tissue fluid. Plant cells are also cultivated and surrounded by a liquid medium in the apoplast. As well as various important functions of the internal environment in our body, apoplast function is also prerequisite for the plant life. There are so far seven distinct functions of apoplast. (1) Growth regulation with apoplastic enzymes by altering cell-wall properties through degradation, synthesis, orientation and cross-linking of supra-molecules of cell walls, such as cellulose, non-cellulosic polysaccharides, proteins, and lignin; (2) Skeleton sustained by cellulose microfibrils, lignin and various types of structural proteins with distinctively high content of hydroxyproline, proline or glycine; (3) Skin to defend symplast from desiccation, pathogens' attack and harmful environmental factors, such as ozone and sulfur dioxide; (4) Transportation route for not only well-known molecules of water, inorganic ions, and sugar, but also plant hormones, oligosaccharides and proteins; (5) Homeostasis of the internal environment by controlling ionic balance, pH and water content; (6) Adhesion of cell to cell; (7) Gas exchange space of leaf for photosynthesis. The present article reviews the recent advances in studies of several aspects of the dynamic function and regulation of apoplast.     

Characteristics of the temperature regulation system in the human body

1. 1. To study a complex biological system such as human temperature regulation, it is necessary to consider both physiological experiments and theoretical analysis.

2. 2. This paper presents the characteristics of this temperature regulation system obtained from a mathematical model, together with experimental data and the influence of exercise and clothing.

3. 3. The experimental results showed a good agreement with the theoretical results.

Hormonal and nutritional regulation of insect fat body development and function

The insect fat body is an organ analogue to vertebrate adipose tissue and liver and functions as a major organ for nutrient storage and energy metabolism. Similar to other larval organs, fat body undergoes a developmental “remodeling” process during the period of insect metamorphosis, with the massive destruction of obsolete larval tissues by programmed cell death and the simultaneous growth and differentiation of adult tissues from small clusters of progenitor cells. Genetic ablation of Drosophila fat body cells during larval‐pupal transition results in lethality at the late pupal stage and changes sizes of other larval organs indicating that fat body is the center for pupal development and adult formation. Fat body development and function are largely regulated by several hormonal (i.e. insulin and ecdysteroids) and nutritional signals, including oncogenes and tumor suppressors in these pathways. Combining silkworm physiology with fruitfly genetics might provide a valuable system to understand the mystery of hormonal regulation of insect fat body development and function. © 2009 Wiley Periodicals, Inc.     

The structure,regulation, and function of human matrix metalloproteinase-13

Matrix metalloproteinase-13 (MMP-13) is a proteolytic enzyme that belongs to a large family of extracellular matrix-degrading endopeptidases that are characterized by a zinc-binding motif at their catalytic sites. MMP-13 has a key role in the MMP activation cascade and appears to be critical in bone metabolism and homeostasis. It also has an important role in tumor invasion and metastasis. This commentary provides a detailed overview of the regulatory mechanisms, structure, and function of human MMP-13 and highlights the key factors involved in the biology of this important molecule.     

Integral mechanisms of regulation of oxygen delivery and consumption in human body

With new algorithms of pattern recognition three types of regulation of oxygen delivery and consumption were studied: at normal regulation, hypo- and hyperfunction of heart. It is shown that a surplus systemic blood flow results in increase of arterio-venous shunt flow. Insufficient blood flow results in increase of arterio-venous gradient of blood oxygen content due to the increase of gradient of oxygen content on both sides of capillary wall and to activating of vasomotor function of microcirculatory arterial bed. Quantitative estimations of shunt and capillary blood flow are obtained.     

The synapsins and the regulation of synaptic function

Synapsin I and II are a family of synaptic vesicle-associated phosphoproteins involved in the short-term regulation of neurotransmitter release. In this review, we discuss a working model for the molecular mechanisms by which the synapsins act. We propose that synapsin I links synaptic vesicles to actin filaments in the presynaptic nerve terminal and that these interactions are modulated by the reversible phosphorylation of synapsin I through various signal transduction pathways. The high degree of homology between the synapsins suggests that some of the functional properties of synapsin I are also shared by synapsin II.     

The phosphatonins and the regulation of phosphate transport and vitamin D metabolism

Phosphate homeostasis is preserved during variations in phosphate intake by short-term intrinsic renal and intestinal adaptations in transport processes, and by more long-term hormonal mechanisms, which regulate the efficiency of phosphate transport in the kidney and intestine. Recently, several phosphaturic peptides such as fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein-4 (sFRP-4), extracellular phosphoglycoprotein (MEPE) and fibroblast growth factor 7 (FGF-7) have been shown to play a pathogenic role in several hypophosphatemic disorders such as tumor-induced osteomalacia (TIO), autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemic rickets (XLH), the McCune-Albright syndrome (MAS) and fibrous dysplasia (FD). These proteins induce phosphaturia and hypophosphatemia in vivo, and inhibit sodium-dependent renal phosphate transport in cultured renal epithelial cells. Interestingly, despite the induction of hypophosphatemia by FGF-23 and sFRP-4 in vivo, serum 1, 25-dihydroxyvitamin D (1alpha,25(OH)(2)D) concentrations are decreased or remain inappropriately normal, suggesting an inhibitory effect of these proteins on 25-hydroxyvitamin D 1alpha-hydroxylase activity. In FGF-23 knockout mice, 25-hydroxyvitamin D 1alpha-hydroxylase expression is increased and elevated serum 1alpha,25(OH)(2)D levels cause significant hypercalcemia and hyperphosphatemia. MEPE, however, increases circulating 1alpha,25(OH)(2)D. Circulating or local concentrations of these peptides/proteins may regulate 25-hydroxyvitamin D 1alpha-hydroxylase activity in renal tissues under physiologic circumstances.     

The mechanism and regulation of dolichyl phosphate biosynthesis in rat liver

Rat liver slices were pulse labeled for 6 min with [3H]mevalonolactone and then chased for 90 min with unlabeled mevalonolactone in order to study the mechanism of dolichyl phosphate biosynthesis. The cholesterol pathway was also monitored and served to verify the pulse-chase. Under conditions in which radioactivity in the methyl sterol fraction chased to cholesterol, radioactivity in alpha-unsaturated polyprenyl (pyro)-phosphate chased almost exclusively into dolichyl (pyro)phosphate. Lesser amounts of radioactivity appeared in alpha-unsaturated polyprenol and dolichol, and neither exhibited significant decline after 90 min of incubation. The relative rates of cholesterol versus dolichyl phosphate biosynthesis were studied in rat liver under four different nutritional conditions using labeled acetate, while the absolute rates of cholesterol synthesis were determined using 3H2O. From these determinations, the absolute rates of dolichyl phosphate synthesis were calculated. The absolute rates of cholesterol synthesis were found to vary 42-fold while the absolute rates of dolichyl phosphate synthesis were unchanged. To determine the basis for this effect, the rates of synthesis of cholesterol and dolichyl phosphate were quantitated as a function of [3H]mevalonolactone concentration. Plots of nanomoles incorporated into the two lipids were nearly parallel, yielding Km values on the order of 1 mM. In addition, increasing concentrations of mevinolin yielded parallel inhibition of incorporation of [3H]acetate into cholesterol and dolichyl phosphate. The specific activity of squalene synthase in liver microsomes from rats having the highest rate of cholesterol synthesis was only 2-fold greater than in microsomes from rats having the lowest rate. Taken together, the results suggest that the maintenance of constant dolichyl phosphate synthesis under conditions of enhanced cholesterogenesis is not due to saturation of the dolichyl phosphate pathway by either farnesyl pyrophosphate or isopentenyl pyrophosphate but coordinate regulation of hydroxymethylglutaryl-CoA reductase and a reaction on the pathway from farnesyl pyrophosphate to cholesterol.     

The role of inorganic phosphate in the regulation of C4 photosynthesis

Inorganic phosphate participates in many fundamental processes within the plant cell. Its broad influence on plant metabolism is related to such key operations as metabolite transport, enzyme regulation and carbohydrate metabolism in general. This review discusses these topics with special emphasis on the role assigned to this ubiquitous anion within the C₄ pathway of photosynthesis.Abbreviations DHAP dihydroxyacetone phosphate - Ga3P glyceraldehyde-3-phosphate - NAD(P)-ME-NAD(P) dependent malic enzyme - PEP phosphoenolpyruvate - 3-PGA 3-phosphoglycerate - PFK and PFP-ATP- and PPi dependent fructose-6-phosphate 1-phosphotransferase - PPDK pyruvate:orthophosphate dikinase - RPPC reductive pentose-phosphate cycle - RuBisCO ribulose bisphosphate carboxylase-oxygenase - SPS sucrose-6-phosphate synthase     

An update on the function and regulation of methylerythritol phosphate and mevalonate pathways and their evolutionary dynamics

Isoprenoids are among the largest and most chemically diverse classes of organic compounds in nature and are involved in the processes of photosynthesis, respiration, growth, development, and plant responses to stress. The basic building block units for isoprenoid synthesis—isopentenyl diphosphate and its isomer dimethylallyl diphosphate—are generated by the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. Here, we summarize recent advances on the roles of the MEP and MVA pathways in plant growth, development and stress responses, and attempt to define the underlying gene networks that orchestrate the MEP and MVA pathways in response to developmental or environmental cues. Through phylogenomic analysis, we also provide a new perspective on the evolution of the plant isoprenoid pathway. We conclude that the presence of the MVA pathway in plants may be associated with the transition from aquatic to subaerial and terrestrial environments, as lineages for its core components are absent in green algae. The emergence of the MVA pathway has acted as a key evolutionary event in plants that facilitated land colonization and subsequent embryo development, as well as adaptation to new and varied environments.     

Brain angiotensin: critical role in the ongoing regulation of body fluid homeostasis and cardiovascular function

The existence of an endogenous brain-angiotensin system and its association with cardiovascular and body water regulation has been recognized for over a decade. Nevertheless, the importance of the brain-angiotensin system to the instantaneous regulation of these processes has not been firmly established. A 5-minute intracerebroventricular (ICV) infusion of the angiotensin antagonist, [Sar1,Thr8]-AII, effectively lowered the blood pressure in normotensive rats. Additionally, application of the selective aminopeptidase inhibitor, bestatin, given alone, resulted in a dramatic increase in blood pressure and a robust drinking response. Both effects were 100% blockable by [Sar1,Thr8]-AII pretreatment. Predictably, an aminopeptidase inhibitor, bestatin, greatly elongated the half-lives of AII and AIII in the cerebroventricles. Since neither of these treatments included the introduction of exogenous angiotensins, we have concluded that perturbations of the endogenous brain-angiotensin system are effective at rapidly influencing both cardiovascular and body fluid homeostasis, thus highlighting the paramount role played by brain angiotensin in their ongoing regulation.     

The regulation and function of protein phosphatases in the brain

Data emerging from a number of different systems indicate that protein phosphatases are highly regulated and potentially responsive to changes in the levels of intracellular second messengers produced by extracellular stimulation. They may therefore be involved in the regulation of many cell functions. The protein phosphatases in the nervous system have not been well studied. However, a number of neuronal-specific regulators (such as DARPP-32 and G-substrate) exist, and brain protein phosphatases appear to have particularly low specific activity, suggesting that neuronal protein phosphatases possess considerable and unique potential for regulation. Several early events following depolarization or receptor activation appear to involve specific dephosphorylations, indicating that regulation of protein phosphatase activity is important for the control of many neuronal functions. This article reviews the current literature concerning the identification, regulation, and function of serine/threonine protein phosphatases in the brain, with particular emphasis on the regulation of the major protein phosphatases, PP1 and PP2A, and their potential roles in modulating neurotransmitter release and postsynaptic responses.