Ca2+ Clearance at Growth Cones Produced by Crayfish Motor Axons in an Explant Culture

2003 ◽  
Vol 89 (6) ◽  
pp. 3225-3234 ◽  
Author(s):  
Nidhi Rumpal ◽  
Gregory A. Lnenicka
Keyword(s):  
Plasma Membrane ◽  
Growth Cones ◽  
Explant Culture ◽  
Motor Axons ◽  
Rapid Decay ◽  
Mitochondrial Inhibitors ◽  
High K ◽  
Explant Cultures ◽  
Regulation Of Growth ◽  
Exchange Activity

Intracellular free Ca2+ concentration ([Ca2+]i) plays an important role in the regulation of growth cone (GC) motility; however, the mechanisms responsible for clearing Ca2+ from GCs have not been examined. We studied the Ca2+-clearance mechanisms in GCs produced by crayfish tonic and phasic motor axons by measuring the decay of [Ca2+]i after a high [K+] depolarizing pulse using fura-2AM. Tonic motor axons regenerating in explant cultures develop GCs with more rapid Ca2+ clearance than GCs from phasic axons. When Na/Ca exchange was blocked by replacing external Na+ with N-methyl-d-glucamine (NMG), [Ca2+]i decay was delayed in both tonic and phasic GCs. Tonic GCs appear to have higher Na/Ca exchange activity than phasic ones since reversal of Na/Ca exchange by lowering external Na+ caused a greater increase in [Ca2+]i for tonic than phasic GCs. Application of the mitochondrial inhibitors, Antimycin A1 (1 μM) and CCCP (10 μM), demonstrated that mitochondrial Ca2+ uptake/release was more prominent in phasic than tonic GCs. When both Na/Ca exchange and mitochondria were inhibited, the plasma membrane Ca2+ ATPase was effective in extruding Ca2+ from tonic, but not phasic GCs. We conclude that Na/Ca exchange plays a prominent role in extruding large Ca2+ loads from both tonic and phasic GCs. High Na/Ca exchange activity in tonic GCs contributes to the rapid decay of [Ca2+]i in these GCs; low rates of Ca2+ extrusion plus the release of Ca2+ from mitochondria prolongs the decay of [Ca2+]i in the phasic GCs.

Ca2+ Clearance at Growth Cones Produced by Crayfish Motor Axons in an Explant Culture

2003 ◽  
Vol 89 (6) ◽  
pp. 3225-3234 ◽  
Author(s):  
Nidhi Rumpal ◽  
Gregory A. Lnenicka
Keyword(s):  
Plasma Membrane ◽  
Growth Cones ◽  
Explant Culture ◽  
Motor Axons ◽  
Rapid Decay ◽  
Mitochondrial Inhibitors ◽  
High K ◽  
Explant Cultures ◽  
Regulation Of Growth ◽  
Exchange Activity

Intracellular free Ca2+ concentration ([Ca2+]i) plays an important role in the regulation of growth cone (GC) motility; however, the mechanisms responsible for clearing Ca2+ from GCs have not been examined. We studied the Ca2+-clearance mechanisms in GCs produced by crayfish tonic and phasic motor axons by measuring the decay of [Ca2+]i after a high [K+] depolarizing pulse using fura-2AM. Tonic motor axons regenerating in explant cultures develop GCs with more rapid Ca2+ clearance than GCs from phasic axons. When Na/Ca exchange was blocked by replacing external Na+ with N-methyl-d-glucamine (NMG), [Ca2+]i decay was delayed in both tonic and phasic GCs. Tonic GCs appear to have higher Na/Ca exchange activity than phasic ones since reversal of Na/Ca exchange by lowering external Na+ caused a greater increase in [Ca2+]i for tonic than phasic GCs. Application of the mitochondrial inhibitors, Antimycin A1 (1 μM) and CCCP (10 μM), demonstrated that mitochondrial Ca2+ uptake/release was more prominent in phasic than tonic GCs. When both Na/Ca exchange and mitochondria were inhibited, the plasma membrane Ca2+ ATPase was effective in extruding Ca2+ from tonic, but not phasic GCs. We conclude that Na/Ca exchange plays a prominent role in extruding large Ca2+ loads from both tonic and phasic GCs. High Na/Ca exchange activity in tonic GCs contributes to the rapid decay of [Ca2+]i in these GCs; low rates of Ca2+ extrusion plus the release of Ca2+ from mitochondria prolongs the decay of [Ca2+]i in the phasic GCs.

Anterior mesendoderm induces mouse Engrailed genes in explant cultures

Development ◽  
1993 ◽  
Vol 118 (1) ◽  
pp. 139-149 ◽  
Author(s):  
S.L. Ang ◽  
J. Rossant
Keyword(s):  
Direct Evidence ◽  
Neural Tissue ◽  
Explant Culture ◽  
Neural Plate ◽  
Explant Cultures ◽  
Neural Marker ◽  
Engrailed Genes ◽  
Anterior Posterior

We have developed germ layer explant culture assays to study the role of mesoderm in anterior-posterior (A-P) patterning of the mouse neural plate. Using isolated explants of ectodermal tissue alone, we have demonstrated that the expression of Engrailed-1 (En-1) and En-2 genes in ectoderm is independent of mesoderm by the mid- to late streak stage, at least 12 hours before their onset of expression in the neural tube in vivo at the early somite stage. In recombination explants, anterior mesendoderm from headfold stage embryos induces the expression of En-1 and En-2 in pre- to early streak ectoderm and in posterior ectoderm from headfold stage embryos. In contrast, posterior mesendoderm from embryos of the same stage does not induce En genes in pre- to early streak ectoderm but is able to induce expression of a general neural marker, neurofilament 160 × 10(3) M(r). These results provide the first direct evidence for a role of mesendoderm in induction and regionalization of neural tissue in mouse.

The zebrafish unplugged gene controls motor axon pathway selection

Development ◽  
2000 ◽  
Vol 127 (10) ◽  
pp. 2099-2111 ◽  
Author(s):  
J. Zhang ◽  
M. Granato
Keyword(s):  
Motor Neuron ◽  
Experimental Studies ◽  
Choice Point ◽  
Growth Cones ◽  
Motor Axon ◽  
Motor Axons ◽  
Independent Mechanism ◽  
Neuron Growth ◽  
Future Path

En route to their targets, motor axons encounter choice points at which they select their future path. Experimental studies predict that at each choice point specialized cells provide local guidance to pathfinding motor axons, however, the identity of these cells and their signals is unknown. Here, we identify the zebrafish unplugged gene as a key component for choice point navigation of pioneering motor axons. We show that in unplugged mutant embryos, motor neuron growth cones reach the choice point but make inappropriate pathway decisions. Analysis of chimeric embryos demonstrates that unplugged activity is produced by a selective group of mesodermal cells located adjacent to the choice point. As the first motor growth cones approach the choice point, these mesodermal cells migrate away, suggesting that unplugged activity influences growth cones by a contact-independent mechanism. These data suggest that unplugged defines a somite-derived signal that elicits differential guidance decisions in motor growth cones.

scholarly journals Regulation of SNAREs by tomosyn and ROCK

2004 ◽  
Vol 166 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Toshiaki Sakisaka ◽  
Takeshi Baba ◽  
Shintaro Tanaka ◽  
Genkichi Izumi ◽  
Masato Yasumi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
G Protein ◽  
Growth Cones ◽  
Snare Complex ◽  
Stable Complex ◽  
Small G Protein ◽  
Leading Edges

Extension of neurites requires the SNARE-dependent fusion of plasmalemmal precursor vesicles with the plasma membrane of growth cones. Here, we show that tomosyn localizes at the palm of growth cones and inhibits the fusion of the vesicles there, thus promoting transport of the vesicles to the plasma membrane of the leading edges of growth cones. Tomosyn localizes because ROCK activated by Rho small G protein phosphorylates syntaxin-1, which increases the affinity of syntaxin-1 for tomosyn and forms a stable complex with tomosyn, resulting in inhibition of the formation of the SNARE complex. In retraction of neurites, tomosyn localizes all over the edges of the neurites and inhibits fusion of the vesicles with the plasma membrane. Thus, tomosyn demarcates the plasma membrane by binding to syntaxin-1 phosphorylated by ROCK, and thereby regulates extension and retraction of neurites.

scholarly journals Na+/H+ Exchange Activity in the Plasma Membrane of Arabidopsis

2003 ◽  
Vol 132 (2) ◽  
pp. 1041-1052 ◽  
Author(s):  
Quan-Sheng Qiu ◽  
Bronwyn J. Barkla ◽  
Rosario Vera-Estrella ◽  
Jian-Kang Zhu ◽  
Karen S. Schumaker
Keyword(s):  
Plasma Membrane ◽  
Exchange Activity

scholarly journals Vasopressin-stimulated Ca2+ influx in rat hepatocytes is inhibited in high-K+ medium

1989 ◽  
Vol 260 (3) ◽  
pp. 821-827 ◽  
Author(s):  
A L Savage ◽  
M Biffen ◽  
B R Martin
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Rat Hepatocytes ◽  
Initial Increase ◽  
Phosphorylase Activity ◽  
Plasma Membrane Potential ◽  
Control Value ◽  
High K ◽  
Increased Activity ◽  
Ca2 Channels

We examined the effects of K+ substitution for Na+ on the response of hepatocytes to vasopressin, and on the hepatocyte plasma-membrane potential. (1) High K+ (114 mM) had no effect on the initial increase in phosphorylase a activity in response to vasopressin, but abolished the ability of the hormone to maintain increased activity beyond 10 min. With increasing concentrations a decrease in the vasopressin response was first observed at 30-50 mM-K+. (2) High K+ (114 mM) had no effect on basal 45Ca2+ influx, but abolished the ability of vasopressin to stimulate influx. This effect was also first observed at a concentration of 30-50 mM-K+. (3) Increasing K+ had little effect on the plasma-membrane potential until a concentration of 40 mM was reached. With further increases in concentration the plasma membrane was progressively depolarized. (4) Replacement of Na+ with N-methyl-D-glucamine+ depolarized the plasma membrane to a much smaller extent than did replacement with K+, and was also much less effective in inhibiting the vasopressin response. (5) The plasma-membrane potential was restored to near the control value by resuspending cells in normal-K+ medium after exposure to high-K+ medium. The effects of vasopressin on phosphorylase activity were also restored. (6) We conclude that the Ca2+ channels responsible for vasopressin-stimulated Ca2+ influx are closed by depolarization of the plasma membrane.

scholarly journals One of the origins of plasma membrane phosphatidylserine in plant cells is a local synthesis by a serine exchange activity

FEBS Letters ◽  
1999 ◽  
Vol 464 (1-2) ◽  
pp. 80-84 ◽  
Author(s):  
Patrick Vincent ◽  
Lilly Maneta-Peyret ◽  
Bénédicte Sturbois-Balcerzak ◽  
Michel Duvert ◽  
Claude Cassagne ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Plant Cells ◽  
Local Synthesis ◽  
Exchange Activity

scholarly journals Synergistic integration of Netrin and ephrin axon guidance signals by spinal motor neurons

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Sebastian Poliak ◽  
Daniel Morales ◽  
Louis-Philippe Croteau ◽  
Dayana Krawchuk ◽  
Elena Palmesino ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Molecular Mechanisms ◽  
Neural Circuit ◽  
Growth Cones ◽  
In Vitro Assays ◽  
Dependent Manner ◽  
Motor Axons ◽  
Spinal Motor Neurons ◽  
Spinal Motor

During neural circuit assembly, axonal growth cones are exposed to multiple guidance signals at trajectory choice points. While axonal responses to individual guidance cues have been extensively studied, less is known about responses to combination of signals and underlying molecular mechanisms. Here, we studied the convergence of signals directing trajectory selection of spinal motor axons entering the limb. We first demonstrate that Netrin-1 attracts and repels distinct motor axon populations, according to their expression of Netrin receptors. Quantitative in vitro assays demonstrate that motor axons synergistically integrate both attractive or repulsive Netrin-1 signals together with repulsive ephrin signals. Our investigations of the mechanism of ephrin-B2 and Netrin-1 integration demonstrate that the Netrin receptor Unc5c and the ephrin receptor EphB2 can form a complex in a ligand-dependent manner and that Netrin–ephrin synergistic growth cones responses involve the potentiation of Src family kinase signaling, a common effector of both pathways.

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