Friso Postma - Academia.edu (original) (raw)

Papers by Friso Postma

Research paper thumbnail of Genetic Dissection of Retinal Pathways Using the Electroretinogram (ERG)

Investigative Ophthalmology & Visual Science, 2007

Research paper thumbnail of Genetic elimination of rod/cone coupling reveals the contribution of the secondary rod pathway to the retinal output

Science Advances, 2022

In the retina, signals originating from rod and cone photoreceptors can reach retinal ganglion ce... more In the retina, signals originating from rod and cone photoreceptors can reach retinal ganglion cells (RGCs)—the output neurons—through different pathways. However, little is known about the exact sensitivities and operating ranges of these pathways. Previously, we created rod- or cone-specific Cx36 knockout (KO) mouse lines. Both lines are deficient in rod/cone electrical coupling and therefore provide a way to selectively remove the secondary rod pathway. We measured the threshold of the primary rod pathway in RGCs of wild-type mice. Under pharmacological blockade of the primary rod pathway, the threshold was elevated. This secondary component was removed in the Cx36 KOs to unmask the threshold of the third rod pathway, still below cone threshold. In turn, the cone threshold was estimated by several independent methods. Our work defines the functionality of the secondary rod pathway and describes an additive contribution of the different pathways to the retinal output.

Research paper thumbnail of JCB: ARTICLE Regulation of connexin43 gap junctional communication by phosphatidylinositol

Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibite... more Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibited upon activation of various G protein– coupled receptors; however, the mechanism is unknown. We show that Cx43-based cell–cell communication is inhibited by depletion of phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) from the plasma membrane. Knockdown of phospholipase Cβ3 (PLCβ3) inhibits PtdIns(4,5)P2 hydrolysis and keeps Cx43 channels open after receptor activation. Using a translocatable 5-phosphatase, we show that PtdIns(4,5)P2 depletion is sufficient to close Cx43 channels. When PtdIns(4,5)P2 is overproduced by

Research paper thumbnail of Genetic Dissection of Rod and Cone Synaptic Inputs to Light Responses of Retinal Ganglion Cells in the Mouse

Investigative Ophthalmology & Visual Science, 2008

Research paper thumbnail of Cone Telodendria Form the Substrate for Photoreceptor Coupling

Investigative Ophthalmology & Visual Science, 2010

Research paper thumbnail of The Rod Connexin is Connexin36

Investigative Ophthalmology & Visual Science, 2016

Research paper thumbnail of Connexin45 Is Expressed in Off Cone Bipolar Cells

Investigative Ophthalmology & Visual Science, 2009

Research paper thumbnail of Technical Performance Verification of Wearable and Home Sensor Devices Monitoring Sleep: Best Practices

Biological Psychiatry, 2020

Background: We previously reported that TSPAN5 SNPs were associated with plasma serotonin concent... more Background: We previously reported that TSPAN5 SNPs were associated with plasma serotonin concentrations which were themselves correlated with selective serotonin reuptake inhibitor treatment outcomes in patients with major depression, and with alcohol use disoder (AUD) risk. This study was designed to explore the biological function of TSPAN5, with a focus on serotonin and kynurenine concentrations in the tryptophan pathway. Methods: Functional genomic studies were performed using five human induced pluripotent stem cell (iPSC) lines. Results: TSPAN5 was downregulated by ethanol and by acamprosatedan FDA approved drug for AUD therapy, resulting in decreased serotonin concentrations in iPSCderived neuron culture media and the down-regulation of DDC, MAOA, MAOB, TPH1, and TPH2. Strikingly, these results were compatible with results obtained after the knockdown of TSPAN5 expression in neurons. Very similar observations were also made in iPSC-derived astrocytes. Mass spectrometry identified proteins related to clathrin and other vesicle related proteins which interacted physically with TSPAN5, indicating that TSPAN5 might play a role in vesicular function in addition to regulating genes associated with serotonin biosynthesis and metabolism. RNA-seq data demonstrated that TSPAN5 knockdown in iPSC-derived astrocytes also significantly influenced kynurenine concentrations as well as the expression of genes associated with immune related pathways. Finally, we also determined that TSPAN5 SNPs were associated with acamprosate treatment outcomes in AUD patients. Conclusions: TSPAN5 can modulate concentrations of major metabolites of tryptophan and CNS immune response. These results highlight novel pharmacogenomic mechanisms underlying response to acamprosate therapy.

Research paper thumbnail of Sphingosine-1-phosphate rapidly induces Rho-dependent neurite retraction: action through a specific cell surface receptor

The EMBO Journal, 1996

Sphingosine-l-phosphate (S1P) is a bioactive lysosphingolipid implicated in mitogenesis and cytos... more Sphingosine-l-phosphate (S1P) is a bioactive lysosphingolipid implicated in mitogenesis and cytoskeletal remodelling, but its mechanism of action is poorly understood. We report here that in N1E-115 neuronal cells, SiP mimics the G protein-coupled receptor agonist lysophosphatidic acid (LPA) in rapidly inducing neurite retraction and soma rounding, a process driven by Rho-dependent contraction of the actin cytoskeleton. SlP is .100-fold more potent than LPA in evoking these shape changes, with an EC50 as low as 1.5 nM. Microinjection of SiP has no effect, neither has addition of sphingosine or ceramide. As with LPA, SiP action is inhibited by suramin and subject to homologous desensitization; however, the responses to SlP and LPA do not show cross-desensitization. We conclude that SiP activates its own high affinity receptor to trigger Rho-regulated cytoskeletal events. Thus, SiP and LPA may belong to an emerging family of bioactive lysophospholipids that act through distinct G proteincoupled receptors to mediate similar actions.

Research paper thumbnail of Serum-induced membrane depolarization in quiescent fibroblasts: activation of a chloride conductance through the G protein-coupled LPA receptor

The EMBO Journal, 1996

contributed equally to this work 4Corresponding author Serum stimulation of quiescent fibroblasts... more contributed equally to this work 4Corresponding author Serum stimulation of quiescent fibroblasts leads to a dramatic depolarization of the plasma membrane; however, the identity of the active serum factor(s) and the underlying mechanism are unknown. We find that this serum activity is attributable to albumin-bound lysophosphatidic acid (LPA) acting on its own G protein-coupled receptor, and that membrane depolarization is due to activation of an anion conductance mediating Cl-efflux. This depolarizing Clcurrent can also be activated by thrombin and neuropeptide receptors; it is distinct from volume-regulated Cl1 currents. Activation of the Clcurrent consistently follows stimulation of phospholipase C and coincides with remodelling of the actin cytoskeleton, which is regulated by the Ras-related GTPase Rho. However, the response is not due to Ca2+/protein kinase C signalling and requires neither Rho nor Ras activation. The results indicate that in quiescent fibroblasts, LPA and other G protein-coupled receptor agonists evoke membrane depolarization by activating a new type of Clchannel through a signalling pathway that is closely associated with phosphoinositide hydrolysis, yet independent of known second messengers.

Research paper thumbnail of Connexin29 Is Uniquely Distributed within Myelinating Glial Cells of the Central and Peripheral Nervous Systems

The Journal of Neuroscience, 2002

Although both Schwann cells and oligodendrocytes express connexin32 (Cx32), the loss of this conn... more Although both Schwann cells and oligodendrocytes express connexin32 (Cx32), the loss of this connexin causes demyelination only in the PNS. To determine whether oligodendrocytes might express another connexin that can function in place of Cx32, we searched for novel CNS-specific connexins using reverse transcriptase-PCR and degenerate primers. We identified Cx29, whose transcript was restricted to brain, spinal cord, and sciatic nerve. Developmental expression of Cx29 mRNA in the CNS paralleled that of other myelin-related mRNAs, including Cx32. In the CNS, Cx29 antibodies labeled the internodal and juxtaparanodal regions of small myelin sheaths, whereas Cx32 staining was restricted to large myelinated fibers. In the PNS, Cx29 expression preceded that of Cx32 and declined to lower levels than Cx32 in adulthood. In adult sciatic nerve, Cx29 was primarily localized to the innermost aspects of the myelin sheath, the paranode, the juxtaparanode, and the inner mesaxon. Cx29 displayed a striking coincidence with Kv1.2 K ϩ channels, which are localized in the axonal membrane. Both Cx29 and Cx32 were found in the incisures. Cx29 expressed in N2A cells did not induce intercellular conductances but did participate in the formation of active channels when coexpressed with Cx32. Together, these data show that Cx29 and Cx32 are expressed by myelinating glial cells with distinct distributions.

Research paper thumbnail of Gap Junctions Contribute to Differential Light Adaptation across Direction-Selective Retinal Ganglion Cells

Neuron, Jan 10, 2018

Direction-selective ganglion cells (DSGCs) deliver signals from the retina to multiple brain area... more Direction-selective ganglion cells (DSGCs) deliver signals from the retina to multiple brain areas to indicate the presence and direction of motion. Delivering reliable signals in response to motion is critical across light levels. Here we determine how populations of DSGCs adapt to changes in light level, from moonlight to daylight. Using large-scale measurements of neural activity, we demonstrate that the population of DSGCs switches encoding strategies across light levels. Specifically, the direction tuning of superior (upward)-preferring ON-OFF DSGCs becomes broader at low light levels, whereas other DSGCs exhibit stable tuning. Using a conditional knockout of gap junctions, we show that this differential adaptation among superior-preferring ON-OFF DSGCs is caused by connexin36-mediated electrical coupling and differences in effective GABAergic inhibition. Furthermore, this adaptation strategy is beneficial for balancing motion detection and direction estimation at the lower sig...

Research paper thumbnail of Sphingosine 1-phosphate signalling through the G-protein-coupled receptor Edg-1

Biochemical Journal, 1998

Sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are structurally related lipid medi... more Sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are structurally related lipid mediators that act on distinct G-protein-coupled receptors to evoke similar responses, including Ca2+ mobilization, adenylate cyclase inhibition, and mitogen-activated protein (MAP) kinase activation. However, little is still known about the respective receptors. A recently cloned putative LPA receptor (Vzg-1/Edg-2) is similar to an orphan Gi-coupled receptor termed Edg-1. Here we show that expression of Edg-1 in Sf9 and COS-7 cells results in inhibition of adenylate cyclase and activation of MAP kinase (Gi-mediated), but not Ca2+ mobilization, in response to S1P. These responses are specific in that (i) S1P action is not mimicked by LPA, and (ii) Vzg-1/Edg-2 cannot substitute for Edg-1. Thus the Edg-1 receptor is capable of mediating a subset of the cellular responses to S1P.

Research paper thumbnail of Lysophosphatidic acid induces neuronal shape changes via a novel, receptor-mediated signaling pathway: similarity to thrombin action

Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1993

Lysophosphatidic acid (LPA) is a mitogenic phospholipid produced by certain activated cells and p... more Lysophosphatidic acid (LPA) is a mitogenic phospholipid produced by certain activated cells and present in serum. LPA stimulates phospholipase C and inhibits adenylate cyclase in its target cells, apparently by activating a specific G-protein-coupled receptor. Here, we demonstrate that LPA causes transient rounding of N1E-115 and NG108-15 neuronal cells accompanied by growth cone collapse and retraction of neurites. The effect of LPA is concentration dependent, being half-maximal at 10-20 nM, and reversibly blocked by suramin, an LPA receptor antagonist. The morphological response to LPA is indistinguishable from that evoked by thrombin or a thrombin receptor-activating peptide (TRP) (K. Jalink and W. H. Moolenaar, J. Cell Biol., 118: 411-419, 1992); yet, LPA and thrombin appear to act through distinct receptors. LPA-induced shape changes, like those induced by thrombin and TRP, are driven by contraction of the cortical actin cytoskeleton and not attributable to prior phospholipid h...

Research paper thumbnail of CHAPTER 15. Emerging Research towards the Understanding and Treatment of Autism

RSC Drug Discovery

Autism and Autism Spectrum Disorders (ASD) are neurodevelopmental disorders affecting social skil... more Autism and Autism Spectrum Disorders (ASD) are neurodevelopmental disorders affecting social skills, communication and behaviour. The prevalence of ASD is now recognized to be approximately 1:100. Although autism etiology is still largely undefined, there is convincing evidence of a familial effect. Significant research efforts are focused on defining genetic etiologies resulting from DNA mutations. This area of research has provoked several theories of autism etiology. One prevailing hypothesis suggests multiple DNA mutations converge on a few molecular pathways that regulate neuronal development and synapse formation to cause autism. Recent scientific findings define the regulation of synaptic protein synthesis as one critical pathway that is altered in several single-gene disorders associated with ASD. Defining the molecular neuropathophysiology underlying autism enables the development of effective therapies to treat the core symptoms of autism. Mechanism-based approaches are currently being tested in human trials. Clinical development of new therapies for autism faces significant challenges including the lack of validated outcome measures for efficacy. Identification of molecular and neurobehavioural biomarkers would directly address some of the clinical challenges faced in treating this heterogeneous patient population and speed development of novel therapeutics.

Research paper thumbnail of Acute loss of Cell–Cell Communication Caused by G Protein–coupled Receptors: A Critical Role for c-Src

Journal of Cell Biology, 1998

Gap junctions mediate cell–cell communication in almost all tissues, but little is known about th... more Gap junctions mediate cell–cell communication in almost all tissues, but little is known about their regulation by physiological stimuli. Using a novel single-electrode technique, together with dye coupling studies, we show that in cells expressing gap junction protein connexin43, cell–cell communication is rapidly disrupted by G protein–coupled receptor agonists, notably lysophosphatidic acid, thrombin, and neuropeptides. In the continuous presence of agonist, junctional communication fully recovers within 1–2 h of receptor stimulation. In contrast, a desensitization-defective G protein–coupled receptor mediates prolonged uncoupling, indicating that recovery of communication is controlled, at least in part, by receptor desensitization. Agonist-induced gap junction closure consistently follows inositol lipid breakdown and membrane depolarization and coincides with Rho-mediated cytoskeletal remodeling. However, we find that gap junction closure is independent of Ca2+, protein kinase ...

Research paper thumbnail of Regulation of connexin43 gap junctional communication by phosphatidylinositol 4,5-bisphosphate

Journal of Cell Biology, 2007

Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibite... more Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibited upon activation of various G protein–coupled receptors; however, the mechanism is unknown. We show that Cx43-based cell–cell communication is inhibited by depletion of phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) from the plasma membrane. Knockdown of phospholipase Cβ3 (PLCβ3) inhibits PtdIns(4,5)P2 hydrolysis and keeps Cx43 channels open after receptor activation. Using a translocatable 5-phosphatase, we show that PtdIns(4,5)P2 depletion is sufficient to close Cx43 channels. When PtdIns(4,5)P2 is overproduced by PtdIns(4)P 5-kinase, Cx43 channel closure is impaired. We find that the Cx43 binding partner zona occludens 1 (ZO-1) interacts with PLCβ3 via its third PDZ domain. ZO-1 is essential for PtdIns(4,5)P2-hydrolyzing receptors to inhibit cell–cell communication, but not for receptor–PLC coupling. Our results show that PtdIns(4,5)P2 is a key regulator of Cx43 channel functi...

Research paper thumbnail of Reversal of Disease-Related Pathologies in the Fragile X Mouse Model by Selective Activation of GABA B Receptors with Arbaclofen

Science Translational Medicine, 2012

Pharmacological activation of the GABA B receptor with arbaclofen in a mouse model of fragile X s... more Pharmacological activation of the GABA B receptor with arbaclofen in a mouse model of fragile X syndrome corrects neuronal defects associated with the disease.

Research paper thumbnail of Pulse-Chase in the Light Microscope

Molecular Interventions, 2002

Research paper thumbnail of Multiple connexins contribute to intercellular communication in the Xenopus embryo

Journal of Cell Science, 2002

To explore the role of gap junctional intercellular communication (GJIC)during Xenopus embryogene... more To explore the role of gap junctional intercellular communication (GJIC)during Xenopus embryogenesis, we utilized the host-transfer and antisense techniques to specifically deplete Cx38, the only known maternally expressed connexin. Cx38-depleted embryos developed normally but displayed robust GJIC between blastomeres at 32-128 cell stages, suggesting the existence of other maternal connexins. Analysis of embryonic cDNA revealed maternal expression of two novel connexins, Cx31 and Cx43.4, and a third,Cx43, that had been previously identified as a product of zygotic transcription. Thus, the early Xenopus embryo contains at least four maternal connexins. Unlike Cx38, expression of Cx31, Cx43 and Cx43.4 continue zygotically. Of these, Cx43.4 is the most abundant, accumulating significantly in neural structures including the brain, the eyes and the spinal cord.

Research paper thumbnail of Genetic Dissection of Retinal Pathways Using the Electroretinogram (ERG)

Investigative Ophthalmology & Visual Science, 2007

Research paper thumbnail of Genetic elimination of rod/cone coupling reveals the contribution of the secondary rod pathway to the retinal output

Science Advances, 2022

In the retina, signals originating from rod and cone photoreceptors can reach retinal ganglion ce... more In the retina, signals originating from rod and cone photoreceptors can reach retinal ganglion cells (RGCs)—the output neurons—through different pathways. However, little is known about the exact sensitivities and operating ranges of these pathways. Previously, we created rod- or cone-specific Cx36 knockout (KO) mouse lines. Both lines are deficient in rod/cone electrical coupling and therefore provide a way to selectively remove the secondary rod pathway. We measured the threshold of the primary rod pathway in RGCs of wild-type mice. Under pharmacological blockade of the primary rod pathway, the threshold was elevated. This secondary component was removed in the Cx36 KOs to unmask the threshold of the third rod pathway, still below cone threshold. In turn, the cone threshold was estimated by several independent methods. Our work defines the functionality of the secondary rod pathway and describes an additive contribution of the different pathways to the retinal output.

Research paper thumbnail of JCB: ARTICLE Regulation of connexin43 gap junctional communication by phosphatidylinositol

Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibite... more Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibited upon activation of various G protein– coupled receptors; however, the mechanism is unknown. We show that Cx43-based cell–cell communication is inhibited by depletion of phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) from the plasma membrane. Knockdown of phospholipase Cβ3 (PLCβ3) inhibits PtdIns(4,5)P2 hydrolysis and keeps Cx43 channels open after receptor activation. Using a translocatable 5-phosphatase, we show that PtdIns(4,5)P2 depletion is sufficient to close Cx43 channels. When PtdIns(4,5)P2 is overproduced by

Research paper thumbnail of Genetic Dissection of Rod and Cone Synaptic Inputs to Light Responses of Retinal Ganglion Cells in the Mouse

Investigative Ophthalmology & Visual Science, 2008

Research paper thumbnail of Cone Telodendria Form the Substrate for Photoreceptor Coupling

Investigative Ophthalmology & Visual Science, 2010

Research paper thumbnail of The Rod Connexin is Connexin36

Investigative Ophthalmology & Visual Science, 2016

Research paper thumbnail of Connexin45 Is Expressed in Off Cone Bipolar Cells

Investigative Ophthalmology & Visual Science, 2009

Research paper thumbnail of Technical Performance Verification of Wearable and Home Sensor Devices Monitoring Sleep: Best Practices

Biological Psychiatry, 2020

Background: We previously reported that TSPAN5 SNPs were associated with plasma serotonin concent... more Background: We previously reported that TSPAN5 SNPs were associated with plasma serotonin concentrations which were themselves correlated with selective serotonin reuptake inhibitor treatment outcomes in patients with major depression, and with alcohol use disoder (AUD) risk. This study was designed to explore the biological function of TSPAN5, with a focus on serotonin and kynurenine concentrations in the tryptophan pathway. Methods: Functional genomic studies were performed using five human induced pluripotent stem cell (iPSC) lines. Results: TSPAN5 was downregulated by ethanol and by acamprosatedan FDA approved drug for AUD therapy, resulting in decreased serotonin concentrations in iPSCderived neuron culture media and the down-regulation of DDC, MAOA, MAOB, TPH1, and TPH2. Strikingly, these results were compatible with results obtained after the knockdown of TSPAN5 expression in neurons. Very similar observations were also made in iPSC-derived astrocytes. Mass spectrometry identified proteins related to clathrin and other vesicle related proteins which interacted physically with TSPAN5, indicating that TSPAN5 might play a role in vesicular function in addition to regulating genes associated with serotonin biosynthesis and metabolism. RNA-seq data demonstrated that TSPAN5 knockdown in iPSC-derived astrocytes also significantly influenced kynurenine concentrations as well as the expression of genes associated with immune related pathways. Finally, we also determined that TSPAN5 SNPs were associated with acamprosate treatment outcomes in AUD patients. Conclusions: TSPAN5 can modulate concentrations of major metabolites of tryptophan and CNS immune response. These results highlight novel pharmacogenomic mechanisms underlying response to acamprosate therapy.

Research paper thumbnail of Sphingosine-1-phosphate rapidly induces Rho-dependent neurite retraction: action through a specific cell surface receptor

The EMBO Journal, 1996

Sphingosine-l-phosphate (S1P) is a bioactive lysosphingolipid implicated in mitogenesis and cytos... more Sphingosine-l-phosphate (S1P) is a bioactive lysosphingolipid implicated in mitogenesis and cytoskeletal remodelling, but its mechanism of action is poorly understood. We report here that in N1E-115 neuronal cells, SiP mimics the G protein-coupled receptor agonist lysophosphatidic acid (LPA) in rapidly inducing neurite retraction and soma rounding, a process driven by Rho-dependent contraction of the actin cytoskeleton. SlP is .100-fold more potent than LPA in evoking these shape changes, with an EC50 as low as 1.5 nM. Microinjection of SiP has no effect, neither has addition of sphingosine or ceramide. As with LPA, SiP action is inhibited by suramin and subject to homologous desensitization; however, the responses to SlP and LPA do not show cross-desensitization. We conclude that SiP activates its own high affinity receptor to trigger Rho-regulated cytoskeletal events. Thus, SiP and LPA may belong to an emerging family of bioactive lysophospholipids that act through distinct G proteincoupled receptors to mediate similar actions.

Research paper thumbnail of Serum-induced membrane depolarization in quiescent fibroblasts: activation of a chloride conductance through the G protein-coupled LPA receptor

The EMBO Journal, 1996

contributed equally to this work 4Corresponding author Serum stimulation of quiescent fibroblasts... more contributed equally to this work 4Corresponding author Serum stimulation of quiescent fibroblasts leads to a dramatic depolarization of the plasma membrane; however, the identity of the active serum factor(s) and the underlying mechanism are unknown. We find that this serum activity is attributable to albumin-bound lysophosphatidic acid (LPA) acting on its own G protein-coupled receptor, and that membrane depolarization is due to activation of an anion conductance mediating Cl-efflux. This depolarizing Clcurrent can also be activated by thrombin and neuropeptide receptors; it is distinct from volume-regulated Cl1 currents. Activation of the Clcurrent consistently follows stimulation of phospholipase C and coincides with remodelling of the actin cytoskeleton, which is regulated by the Ras-related GTPase Rho. However, the response is not due to Ca2+/protein kinase C signalling and requires neither Rho nor Ras activation. The results indicate that in quiescent fibroblasts, LPA and other G protein-coupled receptor agonists evoke membrane depolarization by activating a new type of Clchannel through a signalling pathway that is closely associated with phosphoinositide hydrolysis, yet independent of known second messengers.

Research paper thumbnail of Connexin29 Is Uniquely Distributed within Myelinating Glial Cells of the Central and Peripheral Nervous Systems

The Journal of Neuroscience, 2002

Although both Schwann cells and oligodendrocytes express connexin32 (Cx32), the loss of this conn... more Although both Schwann cells and oligodendrocytes express connexin32 (Cx32), the loss of this connexin causes demyelination only in the PNS. To determine whether oligodendrocytes might express another connexin that can function in place of Cx32, we searched for novel CNS-specific connexins using reverse transcriptase-PCR and degenerate primers. We identified Cx29, whose transcript was restricted to brain, spinal cord, and sciatic nerve. Developmental expression of Cx29 mRNA in the CNS paralleled that of other myelin-related mRNAs, including Cx32. In the CNS, Cx29 antibodies labeled the internodal and juxtaparanodal regions of small myelin sheaths, whereas Cx32 staining was restricted to large myelinated fibers. In the PNS, Cx29 expression preceded that of Cx32 and declined to lower levels than Cx32 in adulthood. In adult sciatic nerve, Cx29 was primarily localized to the innermost aspects of the myelin sheath, the paranode, the juxtaparanode, and the inner mesaxon. Cx29 displayed a striking coincidence with Kv1.2 K ϩ channels, which are localized in the axonal membrane. Both Cx29 and Cx32 were found in the incisures. Cx29 expressed in N2A cells did not induce intercellular conductances but did participate in the formation of active channels when coexpressed with Cx32. Together, these data show that Cx29 and Cx32 are expressed by myelinating glial cells with distinct distributions.

Research paper thumbnail of Gap Junctions Contribute to Differential Light Adaptation across Direction-Selective Retinal Ganglion Cells

Neuron, Jan 10, 2018

Direction-selective ganglion cells (DSGCs) deliver signals from the retina to multiple brain area... more Direction-selective ganglion cells (DSGCs) deliver signals from the retina to multiple brain areas to indicate the presence and direction of motion. Delivering reliable signals in response to motion is critical across light levels. Here we determine how populations of DSGCs adapt to changes in light level, from moonlight to daylight. Using large-scale measurements of neural activity, we demonstrate that the population of DSGCs switches encoding strategies across light levels. Specifically, the direction tuning of superior (upward)-preferring ON-OFF DSGCs becomes broader at low light levels, whereas other DSGCs exhibit stable tuning. Using a conditional knockout of gap junctions, we show that this differential adaptation among superior-preferring ON-OFF DSGCs is caused by connexin36-mediated electrical coupling and differences in effective GABAergic inhibition. Furthermore, this adaptation strategy is beneficial for balancing motion detection and direction estimation at the lower sig...

Research paper thumbnail of Sphingosine 1-phosphate signalling through the G-protein-coupled receptor Edg-1

Biochemical Journal, 1998

Sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are structurally related lipid medi... more Sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) are structurally related lipid mediators that act on distinct G-protein-coupled receptors to evoke similar responses, including Ca2+ mobilization, adenylate cyclase inhibition, and mitogen-activated protein (MAP) kinase activation. However, little is still known about the respective receptors. A recently cloned putative LPA receptor (Vzg-1/Edg-2) is similar to an orphan Gi-coupled receptor termed Edg-1. Here we show that expression of Edg-1 in Sf9 and COS-7 cells results in inhibition of adenylate cyclase and activation of MAP kinase (Gi-mediated), but not Ca2+ mobilization, in response to S1P. These responses are specific in that (i) S1P action is not mimicked by LPA, and (ii) Vzg-1/Edg-2 cannot substitute for Edg-1. Thus the Edg-1 receptor is capable of mediating a subset of the cellular responses to S1P.

Research paper thumbnail of Lysophosphatidic acid induces neuronal shape changes via a novel, receptor-mediated signaling pathway: similarity to thrombin action

Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1993

Lysophosphatidic acid (LPA) is a mitogenic phospholipid produced by certain activated cells and p... more Lysophosphatidic acid (LPA) is a mitogenic phospholipid produced by certain activated cells and present in serum. LPA stimulates phospholipase C and inhibits adenylate cyclase in its target cells, apparently by activating a specific G-protein-coupled receptor. Here, we demonstrate that LPA causes transient rounding of N1E-115 and NG108-15 neuronal cells accompanied by growth cone collapse and retraction of neurites. The effect of LPA is concentration dependent, being half-maximal at 10-20 nM, and reversibly blocked by suramin, an LPA receptor antagonist. The morphological response to LPA is indistinguishable from that evoked by thrombin or a thrombin receptor-activating peptide (TRP) (K. Jalink and W. H. Moolenaar, J. Cell Biol., 118: 411-419, 1992); yet, LPA and thrombin appear to act through distinct receptors. LPA-induced shape changes, like those induced by thrombin and TRP, are driven by contraction of the cortical actin cytoskeleton and not attributable to prior phospholipid h...

Research paper thumbnail of CHAPTER 15. Emerging Research towards the Understanding and Treatment of Autism

RSC Drug Discovery

Autism and Autism Spectrum Disorders (ASD) are neurodevelopmental disorders affecting social skil... more Autism and Autism Spectrum Disorders (ASD) are neurodevelopmental disorders affecting social skills, communication and behaviour. The prevalence of ASD is now recognized to be approximately 1:100. Although autism etiology is still largely undefined, there is convincing evidence of a familial effect. Significant research efforts are focused on defining genetic etiologies resulting from DNA mutations. This area of research has provoked several theories of autism etiology. One prevailing hypothesis suggests multiple DNA mutations converge on a few molecular pathways that regulate neuronal development and synapse formation to cause autism. Recent scientific findings define the regulation of synaptic protein synthesis as one critical pathway that is altered in several single-gene disorders associated with ASD. Defining the molecular neuropathophysiology underlying autism enables the development of effective therapies to treat the core symptoms of autism. Mechanism-based approaches are currently being tested in human trials. Clinical development of new therapies for autism faces significant challenges including the lack of validated outcome measures for efficacy. Identification of molecular and neurobehavioural biomarkers would directly address some of the clinical challenges faced in treating this heterogeneous patient population and speed development of novel therapeutics.

Research paper thumbnail of Acute loss of Cell–Cell Communication Caused by G Protein–coupled Receptors: A Critical Role for c-Src

Journal of Cell Biology, 1998

Gap junctions mediate cell–cell communication in almost all tissues, but little is known about th... more Gap junctions mediate cell–cell communication in almost all tissues, but little is known about their regulation by physiological stimuli. Using a novel single-electrode technique, together with dye coupling studies, we show that in cells expressing gap junction protein connexin43, cell–cell communication is rapidly disrupted by G protein–coupled receptor agonists, notably lysophosphatidic acid, thrombin, and neuropeptides. In the continuous presence of agonist, junctional communication fully recovers within 1–2 h of receptor stimulation. In contrast, a desensitization-defective G protein–coupled receptor mediates prolonged uncoupling, indicating that recovery of communication is controlled, at least in part, by receptor desensitization. Agonist-induced gap junction closure consistently follows inositol lipid breakdown and membrane depolarization and coincides with Rho-mediated cytoskeletal remodeling. However, we find that gap junction closure is independent of Ca2+, protein kinase ...

Research paper thumbnail of Regulation of connexin43 gap junctional communication by phosphatidylinositol 4,5-bisphosphate

Journal of Cell Biology, 2007

Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibite... more Cell–cell communication through connexin43 (Cx43)-based gap junction channels is rapidly inhibited upon activation of various G protein–coupled receptors; however, the mechanism is unknown. We show that Cx43-based cell–cell communication is inhibited by depletion of phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) from the plasma membrane. Knockdown of phospholipase Cβ3 (PLCβ3) inhibits PtdIns(4,5)P2 hydrolysis and keeps Cx43 channels open after receptor activation. Using a translocatable 5-phosphatase, we show that PtdIns(4,5)P2 depletion is sufficient to close Cx43 channels. When PtdIns(4,5)P2 is overproduced by PtdIns(4)P 5-kinase, Cx43 channel closure is impaired. We find that the Cx43 binding partner zona occludens 1 (ZO-1) interacts with PLCβ3 via its third PDZ domain. ZO-1 is essential for PtdIns(4,5)P2-hydrolyzing receptors to inhibit cell–cell communication, but not for receptor–PLC coupling. Our results show that PtdIns(4,5)P2 is a key regulator of Cx43 channel functi...

Research paper thumbnail of Reversal of Disease-Related Pathologies in the Fragile X Mouse Model by Selective Activation of GABA B Receptors with Arbaclofen

Science Translational Medicine, 2012

Pharmacological activation of the GABA B receptor with arbaclofen in a mouse model of fragile X s... more Pharmacological activation of the GABA B receptor with arbaclofen in a mouse model of fragile X syndrome corrects neuronal defects associated with the disease.

Research paper thumbnail of Pulse-Chase in the Light Microscope

Molecular Interventions, 2002

Research paper thumbnail of Multiple connexins contribute to intercellular communication in the Xenopus embryo

Journal of Cell Science, 2002

To explore the role of gap junctional intercellular communication (GJIC)during Xenopus embryogene... more To explore the role of gap junctional intercellular communication (GJIC)during Xenopus embryogenesis, we utilized the host-transfer and antisense techniques to specifically deplete Cx38, the only known maternally expressed connexin. Cx38-depleted embryos developed normally but displayed robust GJIC between blastomeres at 32-128 cell stages, suggesting the existence of other maternal connexins. Analysis of embryonic cDNA revealed maternal expression of two novel connexins, Cx31 and Cx43.4, and a third,Cx43, that had been previously identified as a product of zygotic transcription. Thus, the early Xenopus embryo contains at least four maternal connexins. Unlike Cx38, expression of Cx31, Cx43 and Cx43.4 continue zygotically. Of these, Cx43.4 is the most abundant, accumulating significantly in neural structures including the brain, the eyes and the spinal cord.