Sense and specificity in neuronal calcium signalling

AbstractChanges in the intracellular free calcium concentration ([Ca2+]i) in neurons regulate many and varied aspects of neuronal function over time scales from microseconds to days. The mystery is how a single signalling ion can lead to such diverse and specific changes in cell function. This is partly due to aspects of the Ca2+ signal itself, including its magnitude, duration, localisation and persistent or oscillatory nature. The transduction of the Ca2+ signal requires Ca2+ binding to various Ca2+ sensor proteins. The different properties of these sensors are important for differential signal processing and determine the physiological specificity of Ca2+ signalling pathways. A major factor underlying the specific roles of particular Ca2+ sensor proteins is the nature of their interaction with target proteins and how this mediates unique patterns of regulation. We review here recent progress from structural analyses and from functional analyses in model organisms that have begun to reveal the rules that underlie Ca2+ sensor protein specificity for target interaction. We discuss three case studies exemplifying different aspects of Ca2+ sensor/target interaction. This article is part of a special issue titled the 13th European Symposium on Calcium

Beyond nature vs. nurture in expertise research – comment on Baker & Wattie

The field of expertise is mired in a nature vs. nurture debate. Despite what we now know from behavioral genetics research about the underpinnings of human behavior, some expertise theorists continue to deny or downplay the importance of genetic factors (“innate talent”) in expert performance. In this commentary, we argue that this viewpoint is neither defensible nor productive. Our argument is based on two observations. First, there are always limits on human performance, even among individuals who have engaged in long periods of intensive training. Second, grounded in a neurobiological system that has evolved through natural selection, variation across people in phenotypes reflecting these limits will have a genetic component. We comment on directions for future research to advance the field of expertise

Neuronal calcium sensor proteins: emerging roles in membrane traffic and synaptic plasticity

Ca2+ plays a crucial role in the regulation of neuronal function. Recent work has revealed important functions for two families of neuronally expressed Ca2+ sensor proteins. These include roles in membrane traffic and in alterations in synaptic plasticity underlying changes in behaviour

Evolution and functional diversity of the Calcium Binding Proteins (CaBPs)

The mammalian central nervous system (CNS) exhibits a remarkable ability to process, store, and transfer information. Key to these activities is the use of highly regulated and unique patterns of calcium signals encoded by calcium channels and decoded by families of specific calcium-sensing proteins. The largest family of eukaryotic calcium sensors is those related to the small EF-hand containing protein calmodulin (CaM). In order to maximize the usefulness of calcium as a signaling species and to permit the evolution and fine tuning of the mammalian CNS, families of related proteins have arisen that exhibit characteristic calcium binding properties and tissue-, cellular-, and sub-cellular distribution profiles. The Calcium Binding Proteins (CaBPs) represent one such family of vertebrate specific CaM like proteins that have emerged in recent years as important regulators of essential neuronal target proteins. Bioinformatic analyses indicate that the CaBPs consist of two subfamilies and that the ancestral members of these are CaBP1 and CaBP8. The CaBPs have distinct intracellular localizations based on different targeting mechanisms including a novel type-II transmembrane domain in CaBPs 7 and 8 (otherwise known as calneuron II and calneuron I, respectively). Recent work has led to the identification of new target interactions and possible functions for the CaBPs suggesting that they have multiple physiological roles with relevance for the normal functioning of the CNS

Determination of the Membrane Topology of the Small EF-Hand Ca2+-Sensing Proteins CaBP7 and CaBP8

The CaBPs represent a subfamily of small EF-hand containing calcium (Ca2+)-sensing proteins related to calmodulin that regulate key ion channels in the mammalian nervous system. In a recent bioinformatic analyses we determined that CaBP7 and CaBP8 form an evolutionarily distinct branch within the CaBPs (also known as the calneurons) a finding that is consistent with earlier observations characterising a putative C-terminal transmembrane (TM) spanning helix in each of these proteins which is essential for their sub-cellular targeting to the Golgi apparatus and constitutive secretory vesicles. The C-terminal position of the predicted TM-helix suggests that CaBP7 and CaBP8 could be processed in a manner analogous to tail-anchored integral membrane proteins which exhibit the ability to insert across membranes post-translationally. In this study we have investigated the topology of CaBP7 and CaBP8 within cellular membranes through a combination of trypsin protection and epitope accessibility analyses. Our results indicate that the TM-helices of CaBP7 and CaBP8 insert fully across membranes such that their extreme C-termini are luminal. The observed type-II membrane topology is consistent with processing of CaBP7 and CaBP8 as true tail-anchored proteins. This targeting mechanism is distinct from any other calmodulin related Ca2+-sensor and conceivably underpins unique physiological functions of these proteins

Modulation of phosphatidylinositol 4-phosphate levels by CaBP7 controls cytokinesis in mammalian cells

Calcium and phosphoinositide signaling regulate cell division in model systems, but their significance in mammalian cells is unclear. Calcium-binding protein-7 (CaBP7) is a phosphatidylinositol 4-kinaseIIIβ (PI4KIIIβ) inhibitor required during cytokinesis in mammalian cells, hinting at a link between these pathways. Here we characterize a novel association of CaBP7 with lysosomes that cluster at the intercellular bridge during cytokinesis in HeLa cells. We show that CaBP7 regulates lysosome clustering and that PI4KIIIβ is essential for normal cytokinesis. CaBP7 depletion induces lysosome mislocalization, extension of intercellular bridge lifetime, and cytokinesis failure. These data connect phosphoinositide and calcium pathways to lysosome localization and normal cytokinesis in mammalian cells

Stimulation of NSF ATPase activity during t-SNARE priming

AbstractN-Ethylmaleimide-sensitive factor (NSF) plays a key role in vesicular traffic by disassembling and priming SNARE proteins for their function in docking and fusion. We demonstrate that the ATPase activity of NSF is activated by α-soluble NSF attachment protein (α-SNAP) in a complex with syntaxin 1A. In addition, we show that a construct consisting of the H3 domain of syntaxin 1A (GST-synt(195–263), which does not support NSF disassembly in the presence of MgATP gave a larger stimulation. NSF ATPase activation was specific and did not occur using mutant α-SNAPs unable to bind GST-synt or with mutated C-termini. We suggest that activation of NSF ATPase activity in the SNARE complex may be essential to allow SNARE priming

Specific effects of KChIP3/calsenilin/DREAM, but not KChIPs 1, 2 and 4, on calcium signalling and regulated secretion in PC12 cells

The KChIPs (K+ channel-interacting proteins) are members of the NCS (neuronal calcium sensor) protein family of Ca2+-binding proteins. It is unclear to what extent the KChIPs have distinct functions although they all interact with Kv4 K+ channels. KChIP3 has also been shown to repress transcription of specific genes via binding to DRE (downstream regulatory element) motifs and all KChIPs may share this function. In the present study, we have compared the function of isoforms of the four KChIPs. KChIPs 1–4 were found to stimulate the traffic of Kv4.2 channels to the plasma membrane. KChIP3 expression in PC12 cells resulted in an increase in exocytosis evoked by activation of purinergic receptors. In contrast, KChIPs 1, 2 and 4, although expressed to the same extent, had no effect on secretion. In addition, KChIP3 but not KChIPs 1, 2 and 4 modified the ATP-induced Ca2+ signal resulting in a delay in recovery after the peak Ca2+ elevation and also specifically resulted in down-regulation of the Na+/Ca2+ exchanger NCX3, which could explain the effects on the Ca2+ signal and secretion. Regulation of NCX3 by KChIP3 has been shown to occur via its DREAM (DRE antagonist modulator) function [Gomez-Villafuertes, Torres, Barrio, Savignac, Gabellini, Rizzato, Pintado, Gutierrez-Adan, Mellstrom, Carafoli and Naranjo (2005) J. Neurosci. 25, 10822–10830] suggesting that this activity might depend on the cellular context of expression of the various KChIPs. These results reveal a new role for KChIP3 in the regulation of Ca2+-regulated secretion and also suggest that the functions of each of the KChIPs may be more specialized than previously appreciated

Parents' perspectives on the value of assistance dogs for children with autism spectrum disorder: a cross-sectional study

Objective While there is an emerging literature on the usefulness of assistance dogs for children with autism spectrum disorder (ASD), there is a dearth of quantitative data on the value of assistance dog interventions for the family unit and family functioning. Using previously validated scales and scales developed specifically for this study, we measured parents’/guardians’ perceptions of how having an assistance dog affects: (1) child safety from environmental dangers, (2) public reception of ASD and (3) levels of caregiver strain and sense of competence. We also obtained open-ended response data from parents/guardians on benefits and constraints of having an assistance dog. Setting This study was based in the primary care setting, within the context of a specific accredited assistance dog centre in Ireland. Participants A total of 134 parents/guardians with an assistance dog, and 87 parents of children on the waiting list were surveyed. Primary and secondary outcome measures The primary outcome measures were scores on environmental hazards and public reception scales. The secondary outcome measures were scores on caregiver strain and competence scales. Results Parents/guardians of children who have ASD and an assistance dog rate their child as significantly safer from environmental dangers (p<0.001), perceive that the public act more respectfully and responsibly towards their child (p<0.001) and feel more competent about managing their child (p=0.023) compared with parents on the waiting list. There was a concentration of positive feeling towards assistance dog interventions with particular focus on safety and comfort for children, and a sense of freedom from family restrictions associated with ASD. The amount of dedication and commitment required to care for a dog were viewed as the primary constraints. Conclusions Our findings indicate that parents perceive that assistance dog interventions can be a valuable intervention for families with children who have ASD

AMP-activated protein kinase is a key regulator of acute neurovascular permeability

Many neuronal and retinal disorders are associated with pathological hyperpermeability of the microvasculature. We have used explants of rodent retinae to study acute neurovascular permeability and signal transduction and the role of AMP-activated protein kinase (AMPK). Following stimulation with either vascular endothelial growth factor (VEGF-A) or bradykinin (BK), AMPK was rapidly and strongly phosphorylated and acted as a key mediator of permeability downstream of Ca2+ Accordingly, AMPK agonists potently induced acute retinal vascular leakage. AMPK activation led to phosphorylation of endothelial nitric oxide synthase (eNOS), which in turn increased VE-cadherin phosphorylation on Y685. In parallel, AMPK also mediated phosphorylation of p38 MAP kinase and HSP27, indicating that it regulated paracellular junctions and cellular contractility, both previously associated with endothelial permeability. Endothelial AMPK provided a missing link in neurovascular permeability, connecting Ca2+ transients to the activation of eNOS and p38, irrespective of the permeability-inducing factor used. Collectively, we find that, due to its compatibility with small molecule antagonists/agonists and siRNA, the ex-vivo retina model constitutes a reliable tool to identify and study regulators and mechanism of acute neurovascular permeability