Papers by Paul Letourneau
Abstract. Cellular interactions with fibronectin-treated substrata have a complex molecular basis... more Abstract. Cellular interactions with fibronectin-treated substrata have a complex molecular basis involving multiple domains. A carboxy-terminal cell and heparin binding region of fibronectin (FN) is particularly interesting because it is a strong promoter of neurite
Differences Based on the Effects of Lanthanum Ion
The effects of lanthanum ions (La +++) on the locomotion and adhesion of g lial cells and elongat... more The effects of lanthanum ions (La +++) on the locomotion and adhesion of g lial cells and elongating nerve axons are reported. I.a +++ increases adhesion of both glia and of nerve growth cones to a plastic substratum. La +++ also markedly reduces glia locomotion, but it does not inhibit nerve elongation. Electron-opaque deposits are seen on the cell surface and within cytoplasmic vesicles of gila and nerves cultured in a La+++-containing medium. Possible modes of action for La +++ are discussed, particularly the possibilities that Ca ++ fluxes or Ca ++ involvement in adhesion are altered by La +++. The results are consistent with the hypothesis that cell migration and nerve axon elongation differ in mechanism, with respect to both adhesive interactions and the activity of microfilament systems.
Structural features of fibronectin synthetic peptide FN-C/H II, responsible for cell adhesion, neurite extension, and heparan sulfate binding
Journal of Biological Chemistry, 1993
FN-C/H II (KNNQKSEPLIGRKKT), a heparin-binding peptide derived from the COOH-terminal heparin-bin... more FN-C/H II (KNNQKSEPLIGRKKT), a heparin-binding peptide derived from the COOH-terminal heparin-binding domain of fibronectin, mediates cell adhesion for a variety of cell types and promotes neurite outgrowth. By systematic amino acid substitution of synthetic peptide analogues of FN-C/H II, the basic structural features necessary for activity have been identified in the COOH-terminal residues LIGRKK. This biologically "active" sequence has been located in several other heparin/heparan sulfate-binding proteins and may represent a potential binding motif for sulfated polyanions. NMR structural studies indicate that the COOH-terminal segment of FN-C/H II displays significant multiple-turn or helix-like character suggesting that the RKK sequence may lie on the same surface of the protein, as opposed to alternating in an extended chain motif.
S1-4 Growth cones integrate signaling from multiple guidance cues
Acta Histochemica Et Cytochemica, 2002
Journal of Cell Science, 1996
The extracellular matrix through which growth cones navigate contains molecules, such as chondroi... more The extracellular matrix through which growth cones navigate contains molecules, such as chondroitin sulfate proteoglycan, that can inhibit growth cone advance and induce branching and turning. Growth cone turning is accompanied by rearrangement of the cytoskeleton. To identify changes in the organization of actin filaments and microtubules that occur as growth cones turn, we used time-lapse phase contrast videomicroscopy to observe embryonic chick dorsal root ganglion neuronal growth cones at a substratum border between fibronectin and chondroitin sulfate proteoglycan, in the presence and absence of cytochalasin B. Growth cones were fixed and immunocytochemically labeled to identify actin filaments and dynamic and stable microtubules. Our results suggest that microtubules are rearranged within growth cones to accomplish turning to avoid chondroitin sulfate proteoglycan. Compared to growth cones migrating on fibronectin, turning growth cones were more narrow, and they contained dyna...
Biology of the Nerve Growth Cone
Trends in Neurosciences, 1986
Growth cones are the highly motile tips of growing axons and dendrites. They have held our attent... more Growth cones are the highly motile tips of growing axons and dendrites. They have held our attention ever since Ram6n y Cajal first saw one in the central nervous system of the developing chick and guessed, with characteristic accuracy, at their purpose. That was nearly one hundred years ago and we still have no definitive description of how growth cones move about or how axons and dendrites elongate. Perhaps even further from our grasp is a molecular description of the recognition events involved in synapse formation. Because the growth cone is responsible not only for navigating the axon or dendrite to its destination bet also for recognizing the correct synaptic partner, growth cones are crucial in the development and regeneration of the nervous system. For those interested in these areas this book is essential reading. As the editors point out in their preface, which serves as a potted history of the field, there has been a resurgence of late in growth cone research after a lull of 20 years or so since the heydays of Harrison (who invented tissue culture to study them) and Speidel. They attribute this renascence to the introduction of new and powerful techniques such as time lapse cinematography coupled with high contrast optics and dissociated cell culture. Examples of these techniques as applied to growth cone research and more recently introduced ones such as patch clamping and scanning electron microscopy are represented in the book. The book starts off with an introduction by Trinkaus which cogently argues a place for growth cone motility in the more general context of directional cell movement. This implies that those studying growth cone behaviour would benefit from an awareness of the state of knowledge of other examples of cell movement (and vice versa). It is a pity then that a few papers in this book were not devoted to such pertinent topics as fibroblast movement, chemotaxis in neutrophils or even to microvillus structure. The book is divided up into three sections dealing with in-vivo, in-vitro and electrophysiological aspects. The individual contributions collectively represent the most comprehensive assembly of papers on growth cones so far published. The book is also something of an imaginative publishing venture because it started life as an issue of the Journal of Neuroscience Research (Vol. 13, number 1 /2 ) entirely devoted to invited research papers on growth cones. The consequences of this unusual genesis are that it is very up-todate and the papers have a uniformity of style, in marked contrast to many books of symposia or meetings which it most closely resembles. Several of the papers are mainly descriptive, dealing with such things as the appearance of HRP-filled growth cones /n v./vo .(Mason, Reh and Constantine-Pa~om; Harris et ~/.) ,and, beautifally revealed, in the scanning electron microscope (Roberts and Patton), but these do not bring us noticeably closer to understanding growth cone motility or neurite extension. Studying channels in the growth cone plasma membrane and associated electrical fields or the responses of the growth cone to directly applied substances such as serotonin (Haydon et al.), NGF (Connolly et al., and Gundersen) or substrate bound molecules such as laminin (Hammarback et al.) are already beginning to do so. Two papers are technically ingenious, the first, by Freeman et al., reports the measurement of currents generated by growth cones in culture using a circularly vibrating probe. Ion substitution experiments seem to indicate that a Ca 2+ flux is responsible and the authors postulate that this may be involved in several processes including neurotransmitter release a property now known of growth cones. Importantly, Freeman et al. also show that the threshold for applied current densities necessary to re-direct growth cone movement is several orders of magnitude higher than the endogenous currents. The second paper, by O'Lagne et aL, reports on the morphological and electrophysiological properties of giant growth cones produced by fusion of the neuroae-like clone PC12. These monsters look set to provide us with much useful information. What is conspicuously lacking here, because of past technical difficulties, is a biochemical analysis of growth cones, in particular the contractile apparatus through which, presumably, all factors affecting motility operate. Perhaps the recent development of techniques to isolate growth cones from developing brain will help close this gap. In the meantime this book is highly recommended.
The nerve growth cone
Intrinsic mechanisms of growth cone motility influence of extrinsic factors growth cones in intac... more Intrinsic mechanisms of growth cone motility influence of extrinsic factors growth cones in intact developing systems the growth cone in regeneration.
The Journal of Neuroscience, 1994
The differentiation and morphogenesis of neural tissues involves a diversity of interactions betw... more The differentiation and morphogenesis of neural tissues involves a diversity of interactions between neural cells and their environment. Many potentially important interactions occur with the extracellular matrix (ECM), a complex association of extracellular glycoproteins organized into aggregates and polymers. In this article, we discuss recent findings on neuronal interactions with the ECM and their roles in neural cell migration and neurite growth. First, we examine the expression and putative functions of the molecules of the neural ECM. Second, we discuss cell surface molecules that mediate neural interactions with ECM components. Last, we address proteoglycans (PGs), a diverse class of glycoproteins, present both as ECM components and as cell surface molecules, which may mediate neural interactions with their environment. The best-understood cellular interactions with the ECM are adhesive, mediated by binding between specific cell surface molecules and cell binding domains of ECM components (Strittmater and Fishman, 199 1; Damsky and Werb, 1992). Cellsubstratum adhesion is necessary for major cell movements of neuron morphogenesis, that is, the migrations of neural cells and their precursors and the migratory behavior ofgrowth cones at the extending tips of axons and dendrites. As cells move, adhesive molecules at the surface of the leading edge of a migrating cell or growth cone bind to ligands on other cell surfaces or ECM components. These bonds stabilize filopodia and lamellipodia, and, in some cases, provide anchorage against which cytoskeletal filaments, associated with the plasma membrane, exert forces to pull the cell or growth cone forward. Thus, ECM has been primarily viewed as an adhesive substratum to provide traction for migrating cells and to stabilize the position and, perhaps, the state of differentiation of nonmotile cells. However, the interactions between neural cells and the ECM are not longer regarded as only adhesive or mechanical. Two points are now clear. First, some of these interactions are definitely not adhesive, but, rather, they may even be antiadhesive (Chiquet-Ehrismann, 199 1). Second, evidence has accumulated to indicate that the cell surface molecules that mediate cell-cell and cell-ECM interactions (immunoglobulin superfamily, cad-Preparation of this review was supported by NIH Grants HDI 9950 and NS28807 (P.C.L.), NIH Grant EY0633 l-01 (D.M.S.), and a grant from the American Cancer Society (M.L.C.
The Journal of Neuroscience, 2002
Growing axons during development are guided to their targets by the activity of their growth cone... more Growing axons during development are guided to their targets by the activity of their growth cones. Growth cones integrate positive and negative guidance cues in deciding the direction in which to extend. We demonstrated previously that treatment of embryonic retinal ganglion cells with brain-derived neurotrophic factor (BDNF) protects their growth cones from collapse induced by nitric oxide (NO). BDNF stabilizes growth-cone actin filaments against NO-induced depolymerization. In the present study, we examined the signaling mechanism involved in BDNF-mediated protection. We found that BDNF causes transient activation of protein kinase A (PKA) during the first 5 min of treatment. Treatment with PKA inhibitors before or in conjunction with BDNF treatment blocked the protective effects of BDNF. The effects of BDNF, however, were not blocked when addition of PKA inhibitors was delayed as little as 15 min after BDNF treatment. When cultures raised overnight in BDNF were treated with PKA inhibitors, BDNF-mediated protection did not end, demonstrating that the maintenance of the protective effects of BDNF is independent of PKA activity. The BDNFinduced activation of PKA was required for BDNF-mediated stabilization of growth-cone actin filaments against depolymerization by cytochalasin D. Finally, the initiation and maintenance of the protective effects of BDNF required protein synthesis. Collectively, these data demonstrate that PKA signaling is required only for an early phase of BDNF-mediated protection from NO-induced growth-cone collapse.
The Journal of Neuroscience, 1998
The sprouting of axon collateral branches is important in the establishment and refinement of neu... more The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 m through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead-axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead-axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca 2ϩ fluctuations. These findings implicate neurotrophins as local cues that directly stimulate the formation of collateral axon branches.
Journal of Neuroscience, 2004
The mechanisms by which neurotrophins regulate growth cone motility are unclear. We investigated ... more The mechanisms by which neurotrophins regulate growth cone motility are unclear. We investigated the role of the p75 neurotrophin receptor (p75 NTR ) in mediating neurotrophin-induced increases in filopodial length. Our data demonstrate that neurotrophin binding to p75 NTR is necessary and sufficient to regulate filopodial dynamics. Furthermore, retinal and dorsal root ganglion growth cones from p75 mutant mice are insensitive to neurotrophins but display enhanced filopodial lengths comparable with neurotrophin-treated wild-type growth cones. This suggests unoccupied p75 NTR negatively regulates filopodia length. Furthermore, p75 NTR regulates RhoA activity to mediate filopodial dynamics. Constitutively active RhoA blocks neurotrophin-induced increases in filopodial length, whereas inhibition of RhoA enhances filopodial lengths, similar to neurotrophin treatment. BDNF treatment of retinal neurons results in reduced RhoA activity. Furthermore, p75 mutant neurons display reduced levels of activated RhoA compared with wild-type counterparts, consistent with the enhanced filopodial lengths observed on mutant growth cones. These observations suggest that neurotrophins regulate filopodial dynamics by depressing the activation of RhoA that occurs through p75 NTR signaling.
Journal of Neurobiology, 2003
The motile behaviors of growth cones at the ends of elongating axons determine pathways of axonal... more The motile behaviors of growth cones at the ends of elongating axons determine pathways of axonal connections in developing nervous systems. Growth cones express receptors for molecular guidance cues in the local environment, and receptor-guidance cue binding initiates cytoplasmic signaling that regulates the cytoskeleton to control growth cone advance, turning, and branching behaviors. The dynamic actin filaments of growth cones are frequently targets of this regulatory signaling. Rho GTPases are key mediators of signaling by guidance cues, although much remains to be learned about how growth cone responses are orchestrated by Rho GTPase signaling to change the dynamics of polymerization, transport, and disassembly of actin filaments. Binding of neurotrophins to Trk and p75 receptors on growth cones triggers changes in actin filament dynamics to regulate several aspects of growth cone behaviors. Activation of Trk receptors mediates local accumulation of actin filaments, while neurotrophin binding to p75 triggers local decrease in RhoA signaling that promotes lengthening of filopodia. Semaphorin IIIA and ephrin-A2 are guidance cues that trigger avoidance or repulsion of certain growth cones, and in vitro responses to these proteins include growth cone collapse. Dynamic changes in the activities of Rho GTPases appear to mediate responses to these cues, although it remains unclear what the changes are in actin filament distribution and dynamic reorganization that result in growth cone collapse. Growth cones in vivo simultaneously encounter positive and negative guidance cues, and thus, growth cone behaviors during axonal pathfinding reflect the complex integration of multiple signaling activities.
Journal of Neurobiology, 2000
The morphology of neuronal axons and dendrites is dependent on the dynamics of the cytoskeleton. ... more The morphology of neuronal axons and dendrites is dependent on the dynamics of the cytoskeleton. An understanding of neurodevelopment and adult neuroplasticity must therefore include a detailed description of the intrinsic and extrinsic mechanisms that regulate the organization and dynamics of actin filaments and microtubules. In this paper we review recent advances in the understanding of the dynamic regulation of neuronal morphology by interactions among cytoskeletal components and the regulation of the cytoskeleton by neurotrophins.
Current Biology, 2002
Accurate navigation by a neuronal growth cone requires the modulation of the growth cone's respon... more Accurate navigation by a neuronal growth cone requires the modulation of the growth cone's responsiveness to spatial and temporal changes in expression of guidance cues. These adaptations involve local protein synthesis and turnover in growth cones and distal axons. Local Protein Synthesis at an Intermediate Target Spinal cord commissural axons are attracted to the ventral midline, a source of the attractant netrin. Once
Chemistry & Biology, 1997
Expression of α6 and β4 integrins in serous ovarian carcinoma correlates with expression of the basement membrane protein laminin
The American Journal of Pathology, 1996
Difference in the organization of actin in the growth cones compared with the neurites of cultured n
Cytoskeleton in Axon Growth
eLS, 2016
L1, �1 integrin, and cadherins mediate axonal regeneration in the embryonic spinal cord
J Neurobiol, 2006
The cytoskeleton in growth cone motility and axon pathfinding
Uploads
Papers by Paul Letourneau