scholarly journals Kinetic Model of Translational Autoregulation

2018 ◽  
Author(s):  
Vivian Tyng ◽  
Michael E. Kellman
Keyword(s):  
Steady State ◽  
Phase Space ◽  
Kinetic Model ◽  
Molecular Biology ◽  
Messenger Rna ◽  
Linear Models ◽  
Feedback Mechanism ◽  
Negative Feedback Mechanism ◽  
Feedback Set ◽  
System Phase

AbstractWe investigate dynamics of a kinetic model of inhibitory autoregulation as exemplified when a protein inhibits its own production by interfering with its messenger RNA, known in molecular biology as translational autoregulation. We first show how linear models without feedback set the stage with a nonequilibrium steady state that constitutes the target of the regulation. However, regulation in the simple linear model is far from optimal. The negative feedback mechanism whereby the protein “jams” the mRNA greatly enhances the effectiveness of the control, with response to perturbation that is targeted, rapid, and metabolically efficient. Understanding the full dynamics of the system phase space is essential to understanding the autoregulation process.

Matched rates of insulin infusion and secretion and concurrent tracer-determined rates of glucose appearance and disappearance in fasting dogs

1968 ◽  
Vol 46 (3) ◽  
pp. 383-390 ◽  
Author(s):  
M. Vranic ◽  
G. A. Wrenshall
Keyword(s):  
Steady State ◽  
Insulin Infusion ◽  
Feedback Mechanism ◽  
Negative Feedback Mechanism ◽  
Glucose Levels ◽  
Normal Glucose ◽  
Graft Removal ◽  
Glucose Accumulation ◽  
Hypoglycemic Action ◽  
Diabetic Dog

The endogenous secretion rate of insulin in the dog was matched by an intraportal infusion of exogenous pork insulin at a rate of 12 milliunits/kg h following removal of the remnant pancreatic autograft. Both homeostasis and a dynamic steady state for glucose were observed. An apparent functional relationship between the infusion rates of insulin (7.2–16.4 milliunits/kg h) and the tracer-determined rates of glucose appearance and disappearance was found following graft removal, but not in the diabetic dog after reduction of hyperglycemia. With rates of insulin infusion less than 12 milliunits/kg h the rate of glucose appearance increased and the rate of its disappearance decreased, causing glucose accumulation. Opposite changes were observed with insulin infusion rates from 15 to 156 milliunits/kg h. When the infusion was switched from the portal to a nonsplanchnic vein the dog was more sensitive to the hypoglycemic action of insulin. The switch-off of insulin infusions, maintained for 4.5–7.0 h in the depancreatized dog at different glucose levels, resulted within 2 min in a rise in plasma glucose concentration caused by both underutilization and overproduction of glucose. Overproduction of glucose was still observed 15 h thereafter, when a new steady state was being approached. It is postulated that in the fasting dog at normal glucose levels a continuous insulin secretion of 12 milliunits/kg h is indispensable for the apparent negative feedback mechanism to maintain glucose near the dynamic steady state. In the absence of insulin, the apparent feedback mechanism becomes functional again but at high glucose levels.

An aggregative response of the tropical Australian magpie goose (Anseranas semipalmata) to seasonal floodplains

2011 ◽  
Vol 27 (2) ◽  
pp. 171-180 ◽  
Author(s):  
Lochran W. Traill ◽  
Barry W. Brook
Keyword(s):  
Linear Models ◽  
Feedback Mechanism ◽  
Food Plants ◽  
Supporting Evidence ◽  
Negative Feedback Mechanism ◽  
Extrinsic Parameters ◽  
Aggregative Response ◽  
Plant Herbivore ◽  
The Impact ◽  
Australian Magpie

Abstract:We describe the spatial aggregation of the magpie goose (Anseranas semipalmata) in relation to the dynamics of the ephemeral floodplains of northern Australia. Past broad-scale studies have linked geese to floodplains dominated by the sedge, Eleocharis dulcis, but the type of response has not been determined, nor the impact of predation on food plants. Moreover, departure thresholds are not known. We develop hypotheses on aggregation and departure and confront these with field data. Thus, from 2005–2007 we established two sites on the floodplains of Kakadu National Park (three 1-ha plots per site, six plots in total) and used for monthly, dry season bird counts. An airboat was used to collect data from each of the six plots, including sedge tubers and measures of water level and soil viscosity. Further, we built exclosures (three per site, six in total) to test the impact of herbivory on E. dulcis. Generalized linear models and information theory were used to test the strength of supporting evidence for alternate hypotheses. Geese showed a clear aggregative response to E. dulcis tubers, were forced to depart following floodplain drying and had a marked impact on E. dulcis tuber density. Despite this, there was no evidence of a negative-feedback mechanism between plant–herbivore populations, suggesting that the system is driven by extrinsic parameters (here rainfall).

Ultrastructural morphology of nontumorous lactotrophs in human pituitaries exposed to high prolactin levels

1987 ◽  
Vol 45 ◽  
pp. 896-897
Author(s):  
S. Jalalah ◽  
K. Kovacs ◽  
E. Horvath
Keyword(s):  
Anterior Pituitary ◽  
Secretory Activity ◽  
Pituitary Hormones ◽  
Feedback Mechanism ◽  
Endocrine Activity ◽  
Hormone Synthesis ◽  
Anterior Pituitary Hormones ◽  
Negative Feedback Mechanism ◽  
Ultrastructural Morphology ◽  
Transmission Electron

Lactotrophs, as many other endocrine cells, change their morphology in response to factors influencing their secretory activity. Secretion of prolactin (PRL) from lactotrophs, like that of other anterior pituitary hormones, is under the control of the hypothalamus. Unlike most anterior pituitary hormones, PRL has no apparent target gland which could modulate the endocrine activity of lactotrophs. It is generally agreed that PRL regulates its own release from lactotrophs via the short loop negative feedback mechanism exerted at the level of the hypothalamus or the pituitary. Accordingly, ultrastructural morphology of lactotrophs is not constant; it is changing in response to high PRL levels showing signs of suppressed hormone synthesis and secretion.By transmission electron microscopy and morphometry, we have studied the morphology of lactotrophs in nontumorous (NT) portions of 7 human pituitaries containing PRL-secreting adenoma; these lactotrophs were exposed to abnormally high PRL levels.

The Tangled Tale of Phase Space

2018 ◽  
Author(s):  
David D. Nolte
Keyword(s):  
Phase Space ◽  
Chaotic Behavior ◽  
Three Body Problem ◽  
Henri Poincaré ◽  
History Of ◽  
The Stability ◽  
Three Body ◽  
Space Phase ◽  
Central Paradigm ◽  
System Phase

This chapter presents the history of the development of the concept of phase space. Phase space is the central visualization tool used today to study complex systems. The chapter describes the origins of phase space with the work of Joseph Liouville and Carl Jacobi that was later refined by Ludwig Boltzmann and Rudolf Clausius in their attempts to define and explain the subtle concept of entropy. The turning point in the history of phase space was when Henri Poincaré used phase space to solve the three-body problem, uncovering chaotic behavior in his quest to answer questions on the stability of the solar system. Phase space was established as the central paradigm of statistical mechanics by JW Gibbs and Paul Ehrenfest.

scholarly journals Regulation of Store-Operated Ca2+ Entry by SARAF

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1887
Author(s):  
Inbal Dagan ◽  
Raz Palty
Keyword(s):  
Molecular Mechanisms ◽  
Feedback Mechanism ◽  
Cellular Biology ◽  
Excitable Cells ◽  
Major Pathway ◽  
Negative Feedback Mechanism ◽  
Crac Channels ◽  
Dependent Inactivation ◽  
Crac Channel ◽  
The One

Calcium (Ca2+) signaling plays a dichotomous role in cellular biology, controlling cell survival and proliferation on the one hand and cellular toxicity and cell death on the other. Store-operated Ca2+ entry (SOCE) by CRAC channels represents a major pathway for Ca2+ entry in non-excitable cells. The CRAC channel has two key components, the endoplasmic reticulum Ca2+ sensor stromal interaction molecule (STIM) and the plasma-membrane Ca2+ channel Orai. Physical coupling between STIM and Orai opens the CRAC channel and the resulting Ca2+ flux is regulated by a negative feedback mechanism of slow Ca2+ dependent inactivation (SCDI). The identification of the SOCE-associated regulatory factor (SARAF) and investigations of its role in SCDI have led to new functional and molecular insights into how SOCE is controlled. In this review, we provide an overview of the functional and molecular mechanisms underlying SCDI and discuss how the interaction between SARAF, STIM1, and Orai1 shapes Ca2+ signaling in cells.

scholarly journals Direct observation of a coil-to-helix contraction triggered by vinculin binding to talin

2020 ◽  
Vol 6 (21) ◽  
pp. eaaz4707 ◽  
Author(s):  
Rafael Tapia-Rojo ◽  
Alvaro Alonso-Caballero ◽  
Julio M. Fernandez
Keyword(s):  
Focal Adhesions ◽  
Interaction Force ◽  
Magnetic Tweezers ◽  
Feedback Mechanism ◽  
Force Transmission ◽  
Mechanical Coupling ◽  
Negative Feedback Mechanism ◽  
The Reformation ◽  
Energy Penalty ◽  
First Time

Vinculin binds unfolded talin domains in focal adhesions, which recruits actin filaments to reinforce the mechanical coupling of this organelle. However, it remains unknown how this interaction is regulated and its impact on the force transmission properties of this mechanotransduction pathway. Here, we use magnetic tweezers to measure the interaction between vinculin head and the talin R3 domain under physiological forces. For the first time, we resolve individual binding events as a short contraction of the unfolded talin polypeptide caused by the reformation of the vinculin-binding site helices, which dictates a biphasic mechanism that regulates this interaction. Force favors vinculin binding by unfolding talin and exposing the vinculin-binding sites; however, the coil-to-helix contraction introduces an energy penalty that increases with force, defining an optimal binding regime. This mechanism implies that the talin-vinculin-actin association could operate as a negative feedback mechanism to stabilize force on focal adhesions.

scholarly journals HOPF BIFURCATION FROM NEW-KEYNESIAN TAYLOR RULE TO RAMSEY OPTIMAL POLICY

2020 ◽  
pp. 1-33
Author(s):  
Jean-Bernard Chatelain ◽  
Kirsten Ralf
Keyword(s):  
Hopf Bifurcation ◽  
Optimal Policy ◽  
Ad Hoc ◽  
Taylor Rule ◽  
Dynamic Properties ◽  
Feedback Mechanism ◽  
New Keynesian ◽  
Negative Feedback Mechanism ◽  
Positive Feedback Mechanism ◽  
Forward Looking

This paper compares different implementations of monetary policy in a new-Keynesian setting. We can show that a shift from Ramsey optimal policy under short-term commitment (based on a negative feedback mechanism) to a Taylor rule (based on a positive feedback mechanism) corresponds to a Hopf bifurcation with opposite policy advice and a change of the dynamic properties. This bifurcation occurs because of the ad hoc assumption that interest rate is a forward-looking variable when policy targets (inflation and output gap) are forward-looking variables in the new-Keynesian theory.

Activation of the Na+/K+-ATPase by insulin and glucose as a putative negative feedback mechanism in pancreatic beta-cells

2008 ◽  
Vol 457 (6) ◽  
pp. 1351-1360 ◽  
Author(s):  
M. Düfer ◽  
D. Haspel ◽  
P. Krippeit-Drews ◽  
L. Aguilar-Bryan ◽  
J. Bryan ◽  
...  
Keyword(s):  
Beta Cells ◽  
Negative Feedback ◽  
Pancreatic Beta Cells ◽  
Feedback Mechanism ◽  
Negative Feedback Mechanism
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