Wingful, an extracellular feedback inhibitor of Wingless

Secreted peptide signals control many fundamental processes during animal development. Proper responses to these signals require cognate inducible feedback antagonists. Here we report the identification of a novel Drosophila Wingless (Wg) target gene, wingful (wf), and show that it encodes a potent extracellular feedback inhibitor of Wg. In contrast to the cytoplasmic protein Naked cuticle (Nkd), the only known Wg feedback antagonist, Wf functions during larval stages, when Nkd function is dispensable. We propose that Wf may provide feedback control for the long-range morphogen activities of Wg.

Nested autoinhibitory feedbacks alter the resistance of homeostatic adaptive biochemical networks

Negative feedback control is a ubiquitous feature of biochemical systems, as is time delay between a signal and its response. Negative feedback in conjunction with time delay can lead to oscillations. In a cellular context, it might be beneficial to mitigate oscillatory behaviour to avoid recurring stress situations. This can be achieved by increasing the distance between the parameters of the system and certain thresholds, beyond which oscillations occur. This distance has been termed resistance. Here, we prove that in a generic three-dimensional negative feedback system the resistance of the system is modified by nested autoinhibitory feedbacks. Our system features negative feedbacks through both input-inhibition as well as output-activation, a signalling component with mass conservation and perfect adaptation. We show that these features render the system applicable to biological data, exemplified by the high osmolarity glycerol system in yeast and the mammalian p53 system. Output-activation is better supported by data than input-inhibition and also shows distinguished properties with respect to the system's stimulus. Our general approach might be useful in designing synthetic systems in which oscillations can be tuned by synthetic autoinhibitory feedbacks.

Kisspeptins in human reproduction-future therapeutic potential

OBJECTIVE

Kisspeptins (Kps), were first found to regulate the hypothalamopituitary-gonadal axis (HPG) axis in 2003, when two groups-demonstrated that mutations of GPR54 causes idiopathic hypogonadotropic hypogonadism (IHH) characterized by delayed puberty. Objective of this review is to highlight both animal and human discoveries in KISS1/GPR54 system in last decade and extrapolate the therapeutic potential in humans from till date human studies.

DESIGN

A systematic review of international scientific literature by a search of PUBMED and the authors files was done for Kp in reproduction, metabolic control & signal transduction.

SETTING

None Patient(s): In human studies--normal subjects patients with HH, or HA.

MAIN OUTCOME MEASURES

Effects of Kp on puberty, brain sexual maturation, regulation of GnRH secretion, metabolic control of GnRH Neurons (N).

RESULTS

Kps/GPR54 are critical for brain sexual maturation, puberty and regulation of reproduction. Kps have been implicated in mediating signals to GnRH N--positive and negative feedback, metabolic input. Ability of Kp neurons to coordinate signals impinging on the HPG axis makes it one of most important regulators of reproductive axis since GnRH N's lack many receptors, with Kp neurons serving as upstream modulators.

CONCLUSIONS

Kps have proven as pivotal regulators of the reproduction, with the ability to integrate signals from both internal and external sources. Knowledge about signaling mechanisms involved in Kp stimulation of GnRH and with human studies has made it possible that therapeutically available Kp agonists/antagonists may be used for treatment of delayed puberty/HH, Hypothalamic amenorrhea and in prevention of spread of malignant ovarian/gonadal malignancies along with uses in some eating disorders.

Model-Based Design of a Synthetic Oscillator Based on an Epigenetic Methylation Memory System

Oscillations are an important component in biological systems; grasping their mechanisms and regulation, however, is difficult. Here, we use the theory of dynamical systems to support the design of oscillatory systems based on epigenetic control elements. Specifically, we use results that extend the Poincaré-Bendixson theorem for monotone control systems that are coupled to a negative feedback circuit. The methodology is applied to a synthetic epigenetic memory system based on DNA methylation that serves as a monotone control system, which is coupled to a negative feedback. This system is generally able to show sustained oscillations according to its structure; however, a first experimental implementation showed that fine-tuning of several parameters is required. We provide design support by exploring the experimental design space using systems-theoretic analysis of a computational model.

How Does Escherichia coli Allocate Proteome?

Microorganisms are shown to actively partition their intracellular resources, such as proteins, for growth optimization. Recent experiments have begun to reveal molecular components unpinning the partition; however, quantitatively, it remains unclear how individual parts orchestrate to yield precise resource allocation that is both robust and dynamic. Here, we developed a coarse-grained mathematical framework that centers on guanosine pentaphosphate (ppGpp)-mediated regulation and used it to systematically uncover the design principles of proteome allocation in Escherichia coli. Our results showed that the cellular ability of resource partition lies in an ultrasensitive, negative feedback-controlling topology with the ultrasensitivity arising from zero-order amino acid kinetics and the negative feedback from ppGpp-controlled ribosome synthesis. In addition, together with the time-scale separation between slow ribosome kinetics and fast turnovers of ppGpp and amino acids, the network topology confers the organism an optimization mechanism that mimics sliding mode control, a nonlinear optimization strategy that is widely used in man-made systems. We further showed that such a controlling mechanism is robust against parameter variations and molecular fluctuations and is also efficient for biomass production over time. This work elucidates the fundamental controlling mechanism of E. coli proteome allocation, thereby providing insights into quantitative microbial physiology as well as the design of synthetic gene networks.

Negative feedback neuroendocrine control of inflammatory response in the rat is dependent on the sympathetic postganglionic neuron

Negative feedback control of inflammation is mediated by activation of nociceptive afferents that in turn activates the hypothalamic-pituitary-adrenal axis to release corticosteroids. Plasma extravasation (PE) produced by the potent inflammatory mediator, bradykinin (BK), but not that induced by another potent inflammatory mediator, platelet-activating factor (PAF), is inhibited by released corticosterone. Because bradykinin, but not PAF, produces PE by a mechanism that is, in part, dependent on the sympathetic postganglionic neuron (SPGN) terminal, we tested the hypothesis that the negative feedback control of inflammation is dependent on the SPGN terminal in the inflamed tissue. In sympathectomized rats, the residual (i.e., SPGN-independent) PE in the knee joint produced by BK was not inhibited by noxious electrical stimulation. Furthermore, intravenous administration of corticosterone potently inhibited, with a similar time-course, the SPGN-dependent, but not the SPGN-independent, component of BK-induced PE. Neither electrical stimulation nor corticosterone inhibited PAF-induced PE. Finally, corticosterone's actions do not appear to be mediated by release of norepinephrine from the SPGN terminal, because neither the alpha-adrenergic receptor antagonist phentolamine nor the beta2-adrenergic receptor antagonist ICI 118, 551 antagonized the inhibition of BK-induced PE by corticosterone. We conclude that in the rat knee joint, negative feedback control of the inflammatory response is dependent on the presence of the SPGN terminal. Further, our data suggest that a significant component of corticosteroid-induced inhibition of PE produced by inflammatory mediators is SPGN-dependent.