Shiri Yaniv - Academia.edu (original) (raw)

Papers by Shiri Yaniv

Cell, 2016

During development, neurons switch among growth states, such as initial axon outgrowth, axon prun... more During development, neurons switch among growth states, such as initial axon outgrowth, axon pruning, and regrowth. By studying the stereotypic remodeling of the Drosophila mushroom body (MB), we found that the heme-binding nuclear receptor E75 is dispensable for initial axon outgrowth of MB γ neurons but is required for their developmental regrowth. Genetic experiments and pharmacological manipulations on ex-vivo-cultured brains indicate that neuronally generated nitric oxide (NO) promotes pruning but inhibits regrowth. We found that high NO levels inhibit the physical interaction between the E75 and UNF nuclear receptors, likely accounting for its repression of regrowth. Additionally, NO synthase (NOS) activity is downregulated at the onset of regrowth, at least partially, by short inhibitory NOS isoforms encoded within the NOS locus, indicating how NO production could be developmentally regulated. Taken together, these results suggest that NO signaling provides a switching mechanism between the degenerative and regenerative states of neuronal remodeling.

Neuron, 2015

Developmental axon pruning is essential for normal brain wiring in vertebrates and invertebrates.... more Developmental axon pruning is essential for normal brain wiring in vertebrates and invertebrates. How axon pruning occurs in vivo is not well understood. In a mosaic loss-of-function screen, we found that Bsk, the Drosophila JNK, is required for axon pruning of mushroom body γ neurons, but not their dendrites. By combining in vivo genetics, biochemistry, and high-resolution microscopy, we demonstrate that the mechanism by which Bsk is required for pruning is through reducing the membrane levels of the adhesion molecule Fasciclin II (FasII), the NCAM ortholog. Conversely, overexpression of FasII is sufficient to inhibit axon pruning. Finally, we show that overexpressing other cell adhesion molecules, together with weak attenuation of JNK signaling, strongly inhibits pruning. Taken together, we have uncovered a novel and unexpected interaction between the JNK pathway and cell adhesion and found that destabilization of cell adhesion is necessary for efficient pruning.

The plasticity hypothesis of major depression states that glucocorticoids may be detrimental to n... more The plasticity hypothesis of major depression states that glucocorticoids may be detrimental to neuronal plasticity while monoamines and antidepressants may reconstitute cellular plasticity. The aim of the present study was to investigate how dexamethasone, a synthetic glucocorticoid, and norepinephrine, both of which are involved in depression, interact to affect aspects of neuronal plasticity. Dexamethasone and norepinephrine administered separately oppositely affected differentiation of human neuroblastoma SH-SY5Y cells, observed by both morphological alterations and gene expression, at the level of mRNA and protein of the differentiation markers Gap-43, L1 and laminin. Norepinephrine increased differentiation, manifested as an increase in neurite length, neurite number, and gene expression, while dexamethasone reduced these parameters. Opposite effects were also observed in the expression of the transcription factor CREB with norepinephrine upregulating phosphorylated CREB (pCREB) levels, while dexamethasone downregulated CREB mRNA and protein levels, as well as pCREB levels. Interestingly, co-administration of dexamethasone and norepinephrine resulted in morphology more differentiated than control and similar to that induced by norepinephrine, albeit to a lesser degree. The alterations in the expression of the differentiation markers induced by norepinephrine or dexamethasone treatments were mostly annulled by the co-treatment. However, pCREB levels were robustly enhanced by co-treatment, as compared to both control and norepinephrine treated cells, providing a possible explanation for the morphological increase in differentiation. These results suggest that in order for cells to combat the deleterious effects of glucocorticoids, a hyperactivation of pCREB may be necessary to restore differentiation and plasticity.

PLoS ONE, 2014

Axon pruning is an evolutionarily conserved strategy used to remodel neuronal connections during ... more Axon pruning is an evolutionarily conserved strategy used to remodel neuronal connections during development. The Drosophila mushroom body (MB) undergoes neuronal remodeling in a highly stereotypical and tightly regulated manner, however many open questions remain. Although it has been previously shown that glia instruct pruning by secreting a TGFb ligand, myoglianin, which primes MB neurons for fragmentation and also later engulf the axonal debris once fragmentation has been completed, which glia subtypes participate in these processes as well as the molecular details are unknown. Here we show that, unexpectedly, astrocytes are the major glial subtype that is responsible for the clearance of MB axon debris following fragmentation, even though they represent only a minority of glia in the MB area during remodeling. Furthermore, we show that astrocytes both promote fragmentation of MB axons as well as clear axonal debris and that this process is mediated by ecdysone signaling in the astrocytes themselves. In addition, we found that blocking the expression of the cell engulfment receptor Draper in astrocytes only affects axonal debris clearance. Thereby we uncoupled the function of astrocytes in promoting axon fragmentation to that of clearing axonal debris after fragmentation has been completed. Our study finds a novel role for astrocytes in the MB and suggests two separate pathways in which they affect developmental axon pruning.

European Neuropsychopharmacology, 2007

European Neuropsychopharmacology, 2006

European Journal of Pharmacology, 2008

European Journal of Cell Biology, 2010

Norepinephrine (NE) and glucocorticoids (GCs) have been shown to oppositely affect various aspect... more Norepinephrine (NE) and glucocorticoids (GCs) have been shown to oppositely affect various aspects of neuronal plasticity. These findings provided the basis for the plasticity hypothesis of major depression, which suggests that the disease-related impairment in neuronal plasticity is associated with long-term increase in GCs and may be reconstituted by antidepressants and monoamines. To investigate the interaction between GCs and NE, the plasticity-relevant ERK/MAPK pathway was studied in SH-SY5Y neuroblastoma cells treated with dexamethasone (DEX), a synthetic GC, NE, or both. NE treatment activated ERK and c-Jun and increased AP-1 transcriptional activity. Although DEX had no effect, co-treatment caused a prolonged and robust activation of the ERK/AP-1 pathway beyond NE-induced activation. Co-treatment also induced hyperactivation of CREB as compared to NE activation while DEX decreased pCREB. Independent alterations of ERK and CREB suggest an upstream point of interaction. Yohimbine, an alpha(2)-adrenergic receptor (AR) antagonist, prevented the hyperactivation of the ERK/AP-1 pathway and CREB induced by co-treatment. Immunofluorescence showed that after 2h of NE treatment, beta-arrestin was co-localized with the alpha(2)-AR at the plasma membrane while following co-treatment beta-arrestin was diffused within the cell, suggesting that DEX delays AR downregulation by altering beta-arrestin translocation. These results show a novel complex interaction by which GCs augment NE-induced intracellular signaling that may be relevant to antidepressant mode of action.

Current Biology, 2012

Background: The molecular mechanisms that determine axonal growth potential are poorly understood... more Background: The molecular mechanisms that determine axonal growth potential are poorly understood. Intrinsic growth potential decreases with age, and thus one strategy to identify molecular pathways controlling intrinsic growth potential is by studying developing young neurons. The programmed and stereotypic remodeling of Drosophila mushroom body (MB) neurons during metamorphosis offers a unique opportunity to uncover such mechanisms. Despite emerging insights into MB g-neuron axon pruning, nothing is known about the ensuing axon re-extension. Results: Using mosaic loss of function, we found that the nuclear receptor UNF (Nr2e3) is cell autonomously required for the re-extension of MB g-axons following pruning, but not for the initial growth or guidance of any MB neuron type. We found that UNF promotes this process of developmental axon regrowth via the TOR pathway as well as a late axon guidance program via an unknown mechanism. We have thus uncovered a novel developmental program of axon regrowth that is cell autonomously regulated by the UNF nuclear receptor and the TOR pathway. Conclusions: Our results suggest that UNF activates neuronal re-extension during development. Taken together, we show that axon growth during developmental remodeling is mechanistically distinct from initial axon outgrowth. Due to the involvement of the TOR pathway in axon regeneration following injury, our results also suggests that developmental regrowth shares common molecular mechanisms with regeneration following injury. *Correspondence: oren.schuldiner@weizmann.ac.il Please cite this article in press as: Yaniv et al., Axon Regrowth during Development and Regeneration Following Injury Share Molecular Mechanisms, Current Biology (2012), http://dx.

Brain Research Bulletin, 2004

Prenatal exposure of mice to heroin (SC injection of 10 mg/kg to the dams on gestational days 9-1... more Prenatal exposure of mice to heroin (SC injection of 10 mg/kg to the dams on gestational days 9-18) resulted at adulthood in behavioral deficits related to septohippocampal cholinergic innervation accompanied with both presynaptic and postsynaptic cholinergic hyperactivity; including an increase membrane PKC activity, and a desensitization of PKC to cholinergic input which were highly correlated with the behavioral performance and were reversed by cholinergic grafting. Therefore, we studied the receptor induced activation of the behaviorally relevant PKC␥ and PKC␤II isoforms and the less behaviorally relevant PKC␣ isoform. Time course studies revealed peak translocation after 40 min incubation with carbachol for PKC␥ (110% increase from basal, i.e. no carbachol level, P < 0.01), 30 min for phosphorylated PKC␤II (130%, P < 0.05) and 5 min for non-phosphorylated PKC␤II (64%, P < 0.05) with no peak for alpha. Prenatal heroin abolished the translocation of PKC␥ and PKC␤II while PKC␣ remained unaffected. A decrease occurred in basal phosphorylated membrane (−45%, P < 0.01) and cytosol-associated (−29%, P < 0.01) PKC␤II, in membrane-associated non-phosphorylated PKC␤II (−32%, P < 0.01) and PKC␥ (−25%, P < 0.01) and in cytosolic PKC␣ (−27%, P < 0.01), while membrane-associated PKC␣ was slightly increased (11%, P < 0.05). The results suggest that prenatal heroin disrupts cholinergic receptor induced PKC translocation and activation with the underlying mechanism of neuroteratogenicity potentially lying in the PKC␥ and PKC␤II, while PKC␣ remains unaffected.

Annals of the New York Academy of Sciences, 2004

Although the actions of heroin on central nervous system (CNS) development are mediated through o... more Although the actions of heroin on central nervous system (CNS) development are mediated through opioid receptors, the net effects converge on dysfunction of cholinergic systems. We explored the mechanisms underlying neurobehavioral deficits in mouse and avian (chick, Cayuga duck) models. In mice, prenatal heroin exposure (10 mg/kg on gestation days 9-18) elicited deficits in behaviors related to hippocampal cholinergic innervation, characterized by concomitant pre-and postsynaptic hyperactivity, but ending in a reduction of basal levels of protein kinase C (PKC) isoforms ␤II and ␥ and their desensitization to cholinergic receptor-induced activation. PKC␣, which is not involved in the behaviors studied, was unaffected. Because mammalian models possess inherent confounding factors from maternal effects, we conducted parallel studies using avian embryos, evaluating hyperstriatal nucleus (intermedial part of the hyperstriatum ventrale, IMHV)-related, filial imprinting behavior. Heroin injection to the eggs (20 mg/kg) on incubation days 0 and 5 diminished the post-hatch imprinting ability and reduced PKC␥ and ␤II content in the IMHV membrane fraction. Two otherwise unrelated agents that converge on cholinergic systems, chlorpyrifos and nicotine, elicited the same spectrum of effects on PKC isoforms and imprinting but had more robust actions. Pharmacological characterization also excluded direct effects of opioid receptors on the expression of imprinting; instead, it indicated participation of serotonergic innervation. The avian models can provide rapid screening of neuroteratogens, exploration of common mechanisms of behavioral disruption, and the potential design of therapies to reverse neurobehavioral deficits.

The international journal of neuropsychopharmacology / official scientific journal of the Collegium Internationale Neuropsychopharmacologicum (CINP), 2003

Opioid drugs act primarily on the opiate receptors; they also exert their effect on other innerva... more Opioid drugs act primarily on the opiate receptors; they also exert their effect on other innervations resulting in non-opioidergic behavioural deficits. Similarly, opioid neurobehavioural teratogenicity is attested in numerous behaviours and neural processes which hinder the research on the mechanisms involved. Therefore, in order to be able to ascertain the mechanism we have established an animal (mouse) model for the teratogenicity induced by opioid abuse, which focused on behaviours related to specific brain area and innervation. Diacetylmorphine (heroin) and not morphine was applied because heroin exerts a unique action, distinguished from that of morphine. Pregnant mice were exposed to heroin (10 mg/kg per day) and the offspring were tested for behavioural deficits and biochemical alterations related to the septohippocampal cholinergic innervation. Some studies employing the chick embryo were concomitantly added as a control for the confounding indirect variables. Prenatal exp...