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Biomedical subjects

E T Stoeckli

Publications and source records attributed to E T Stoeckli.

At least 19 recordsLinked to original sources
PubMed2001

Distinct subpopulations of sensory afferents require F11 or axonin-1 for growth to their target layers within the spinal cord of the chick.

Dorsal root ganglion neurons project axons to specific target layers in the gray matter of the spinal cord, according to their sensory modality. Using an in vivo approach, we demonstrate an involvement of the two immunoglobulin superfamily cell adhesion molecules axonin-1/TAG-1 and F11/F3/contactin in subpopulation-specific sensory axon guidance. Proprioceptive neurons, which establish connections with motoneurons in the ventral horn, depend on F11 interactions. Nociceptive fibers, which target to layers in the dorsal horn, require axonin-1 for pathfinding. In vitro NgCAM and NrCAM were shown to bind to both axonin-1 and F11. However, despite this fact and despite their ubiquitous expression in the spinal cord, NgCAM and NrCAM are selective binding partners for axonin-1 and F11 in sensory axon guidance. Whereas nociceptive pathfinding depends on NgCAM and axonin-1, proprioceptive fibers require NrCAM and F11.

Animals↗
PubMed2000

A direct interaction of axonin-1 with NgCAM-related cell adhesion molecule (NrCAM) results in guidance, but not growth of commissural axons.

An interaction of growth cone axonin-1 with the floor-plate NgCAM-related cell adhesion molecule (NrCAM) was shown to play a crucial role in commissural axon guidance across the midline of the spinal cord. We now provide evidence that axonin-1 mediates a guidance signal without promoting axon elongation. In an in vitro assay, commissural axons grew preferentially on stripes coated with a mixture of NrCAM and NgCAM. This preference was abolished in the presence of anti-axonin-1 antibodies without a decrease in neurite length. Consistent with these findings, commissural axons in vivo only fail to extend along the longitudinal axis when both NrCAM and NgCAM interactions, but not when axonin-1 and NrCAM or axonin-1 and NgCAM interactions, are perturbed. Thus, we conclude that axonin-1 is involved in guidance of commissural axons without promoting their growth.

Animals↗
PubMed2000

Use of lipophilic dyes in studies of axonal pathfinding in vivo.

Fluorescent lipophilic dyes are an ideal tool to study axonal pathfinding. Because these dyes do not require active axonal transport for their spreading, they can be used in fixed tissue. Here, we describe the method we have used to study the molecular mechanisms of commissural axon pathfinding in the embryonic chicken spinal cord in vivo. Based on in vitro studies, different families of molecules had been suggested to play a role in the guidance of developing axons. In order to test their function in vivo, we used the commissural neurons that are located at the dorsolateral border of the chicken spinal cord as a model system [Stoeckli and Landmesser (1995) Neuron 14:1165-1179]. Axonin-1, NgCAM, and NrCAM, three members of the immunoglobulin (Ig) superfamily of cell adhesion molecules (CAMs), were shown to be important for the correct growth pattern of commissural axons. We studied the effect of perturbations of specific CAM/CAM interactions by injection of function-blocking antibodies into the central canal of the spinal cord in ovo. After 2 days, the embryos were sacrificed and fluorescent tracers, such as Fast-DiI, were used to visualize commissural axons, and thus, to analyze their response to these perturbations in two different types of fixed preparations: transverse vibratome sections and whole-mount preparations of the spinal cord. Both pathfinding errors and defasciculation of axons were observed as a result of the perturbation of CAM/CAM interactions.

Animals↗
PubMed1998

Axon guidance at choice points.

The common theme in many recent axonal pathfinding studies, both in vertebrates and invertebrates, is the demonstration of the importance of a balance between positive and negative cues. The integration of multiple and often opposing molecular interactions at each site along the axon's trajectory, especially at choice points, helps to fine tune the directional response of its growth cone, which continuously samples its environment for guidance cues. The dynamic regulation of the receptors for such cues, in response to extrinsic signals, also enhances the behavioral repertoire of growth cones at different points along their trajectory. Some of the molecules identified as being important for axon guidance at choice points are conserved between invertebrates and vertebrates (e.g. Robo and netrin), whereas other molecules have been identified, so far, only in invertebrates (e.g. Comm) or vertebrates (e.g. axonin-1 and NrCAM).

Animals↗
PubMed1997

Phenotype of mice lacking functional Deleted in colorectal cancer (Dcc) gene.

The DCC (Deleted in colorectal cancer) gene was first identified as a candidate for a tumour-suppressor gene on human chromosome 18q. More recently, in vitro studies in rodents have provided evidence that DCC might function as a receptor for the axonal chemoattractant netrin-1. Inactivation of the murine Dcc gene caused defects in axonal projections that are similar to those observed in netrin-1-deficient mice but did not affect growth, differentiation, morphogenesis or tumorigenesis in mouse intestine. These observations fail to support a tumour-suppressor function for Dcc, but are consistent with the hypothesis that DCC is a component of a receptor for netrin-1.

Animals↗
PubMed1997

Molecular mechanisms of growth cone guidance: stop and go?

Evidence from pathfinding studies in both vertebrates and invertebrates indicates that growth cones are not guided by simple stop or go signals. Rather, the navigation of growth cones through the preexisting tissue is controlled by a continuous integration of both positive and negative cues. The path taken by an axon is determined by the continuously changing situation encountered by the growth cone at any given site along the trajectory of the axon to the target. The signals derived from interactions of surface molecules with these cues provided by the environment of the growth cone are constantly changing both temporally and spatially. Therefore, each growth cone encounters a unique set of guidance cues directing it to its specific target, thus allowing for the tremendous complexity required for the guidance of millions of axons in the developing nervous system.

Animals↗
PubMed1997

Interference with axonin-1 and NrCAM interactions unmasks a floor-plate activity inhibitory for commissural axons.

Axonin-1 and NrCAM were previously shown to be involved in the in vivo guidance of commissural growth cones across the floor plate of the embryonic chicken spinal cord. To further characterize their role in axon pathfinding, we developed a two-dimensional coculture system of commissural and floor-plate explants in which it was possible to study the behavior of growth cones upon floor-plate contact. Although commissural axons readily entered the floor plate under control conditions, perturbations of either axonin-1 or NrCAM interactions prevented the growth cones from entering the floor-plate explants. The presence of antiaxonin-1 resulted in the collapse of commissural growth cones upon contact with the floor plate. The perturbation of NrCAM interactions also resulted in an avoidance of the floor plate, but without inducing growth-cone collapse. Therefore, axonin-1 and NrCAM are crucial for the contact-mediated interaction between commissural growth cones and the floor plate, which in turn is required for the proper guidance of the axons across the ventral midline and their subsequent rostral turn into the longitudinal axis.

Animals↗
PubMed1996

Clustering and functional cooperation of Ng-CAM and axonin-1 in the substratum-contact area of growth cones.

Growth cones and neurites of chicken dorsal root ganglia neurons cultured on laminin, Ng-CAM, or axonin-1 exhibit substratum-dependent morphology and growth patterns which are accompanied by distinctive distributions of axonin-1 and Ng-CAM in the growth cone membrane. On either Ng-CAM or axonin-1 substratum, both Ng-CAM and axonin-1 were depleted from some areas of the apical growth cone membrane. In contrast, on laminin, both axonin-1 and Ng-CAM remained randomly distributed. Removal of axonin-1 from growth cones resulted in a blockage of neurite outgrowth on both Ng-CAM and axonin-1 substrata, indicating that in these neurons axonin-1 cooperates with Ng-CAM in the activation of axon growth. Based on these results possible molecular models for cooperation between axonin-1 and Ng-CAM on the growth cone are discussed.

Animals↗
PubMed1996

Neuroserpin, an axonally secreted serine protease inhibitor.

We have identified and chromatographically purified an axonally secreted glycoprotein of CNS and PNS neurons. Several peptides derived from it were microsequenced. Based on these sequences, a fragment of the corresponding cDNA was amplified and used as a probe to isolate a full length cDNA from a chicken brain cDNA library. Because the deduced amino acid sequence qualified the protein as a novel member of the serpin family of serine protease inhibitors, we called it neuroserpin. Analysis of the primary structural features further characterized neuroserpin as a heparin-independent, functional inhibitor of a trypsin-like serine protease. In situ hybridization revealed a predominantly neuronal expression during the late stages of neurogenesis and in the adult brain in regions which exhibit synaptic plasticity. Thus, neuroserpin might function as an axonally secreted regulator of the local extracellular proteolysis involved in the reorganization of the synaptic connectivity during development and synapse plasticity in the adult.

Amino Acid Sequence↗
PubMed1995

Axonin-1, Nr-CAM, and Ng-CAM play different roles in the in vivo guidance of chick commissural neurons.

Immunoglobulin/fibronectin type III-like cell adhesion molecules have been implicated in axon pathfinding based on their expression pattern in the developing nervous system and on their complex interactions described in vitro. The present in vivo study demonstrates that interactions by two of these molecules, axonin-1 on commissural growth cones and Nr-CAM on floor plate cells, are required for accurate pathfinding at the midline. When axonin-1 or Nr-CAM interactions were perturbed, many commissural axons failed to cross the midline and turned instead along the ipsilateral floor plate border. In contrast, though perturbation of Ng-CAM produced a defasciculation of the commissural neurites, it did not affect their guidance across the floor plate.

Animals↗
PubMed1994

Distribution of TAG-1/axonin-1 in fibre tracts and migratory streams of the developing mouse nervous system.

The axonal cell adhesion molecule, TAG-1/axonin-1, stimulates axonal growth and supports neurite fasciculation in vitro. Using a polyclonal antiserum raised against chick axonin-1, which shares 75% of its sequence with TAG-1 of the rat, we have mapped the distribution of TAG-1/axonin-1 throughout the developing nervous system of the mouse. Although absent from proliferating neuroepithelia and from non-neuronal cells, immunoreactivity for TAG-1/axonin-1 is expressed by stage-specific subpopulations of differentiating neurons from embryonic day 10 to postnatal day 15. It stains their axons and the surface of their parent somata during the early phases of axogenesis. In agreement with a putative role of TAG-1/axonin-1 as an axon-bound growth substrate, immunoreactivity is found in developing spinal and cranial nerves, in corticothalamic projections, as well as in subsets of fasciculating long projecting tracts of the central nervous system, such as the dorsal funiculi of the spinal cord, the lateral olfactory and optic tracts, the fasciculus retroflexus, and the predorsal bundle. High levels of immunoreactivity characterise the development of the cerebellar molecular layer, the corpus callosum, anterior and hippocampal commissure, and of crossed projections in the spinal cord and at several levels of the brainstem. Intense immunoreactivity in fine collaterals of cutaneous afferents, including their growth cones that are in contact with the embryonic skin, suggests a role of TAG-1/axonin-1 in target recognition. While staining is weak on the somata of radially migrating neurons such as cortical neurons and cerebellar granule cells, strong immunoreactivity is associated with neural somata and processes of the three tangential migrations that form the precerebellar nuclei, indicating a possible involvement of TAG-1/axonin-1 in contacts between these neurons and the processes they migrate upon.

Aging↗
PubMed1993

Cell-cell adhesion by homophilic interaction of the neuronal recognition molecule axonin-1.

The axonal surface glycoprotein axonin-1, which occurs both as a glycosyl-phosphatidylinositol-anchored membrane-bound form and a secreted form, promotes neurite outgrowth and is thought to be involved in axon-guidance mechanisms in the developing nervous system. Recently, we have demonstrated that the neurite-outgrowth-promoting activity of axonin-1, presented as a substratum for cultured neurons, is mediated by a heterophilic interaction with the axonal glycoprotein neuronglia cell-adhesion molecule (Ng-CAM). Here we present evidence for homophilic (like-like) binding among axonin-1 molecules. Axonin-1 was heterologously expressed in myeloma cells. Clonal cell lines, with exposed membrane-bound axonin-1 at their surface, formed large multicellular aggregates. Incubations of transfected and parental myeloma cells, under a series of different conditions, revealed homophilic axonin-1/axonin-1 interactions across the intermembrane space as the molecular mechanism promoting stable cell-cell contacts. Using structural and functional characterisation, recombinant axonin-1 was very similar to native axonin-1, suggesting that homophilic axonin-1 interactions are also established in neurons. The capability of axonin-1 to interact with both Ng-CAM and other axonin-1 molecules might contribute to the formation of macromolecular networks at contact sites of growth cones and axons, comprising molecules of both membranes, and thus represent a mechanism for regulating neurite outgrowth and pathfinding.

Animals↗
PubMed1993

cDNA cloning, structural features, and eucaryotic expression of human TAG-1/axonin-1.

Axonal surface glycoproteins, composed of repeated immunoglobulin-like and fibronectin-type-III(FNIII)-like domains, mediate adhesion between axons or between axons and non-neuronal cells or extracellular matrix proteins. Several representatives of this group promote neurite outgrowth, when presented as substratum to neurons in culture, and have been implicated in axonal guidance mechanisms. TAG-1 and axonin-1 are presumptive species homologues of the rat and the chick, respectively; together with F11/F3, they form a subgroup of Ig/FNIII-like molecules containing a glycosyl-PtdIns membrane anchor. Recent reports on tumor suppressor genes encoding Ig-like and FNIII-like sequences prompted us to isolate the human homologue to TAG-1 and axonin-1. Polymerase chain reaction (PCR) primers were designed to regions conserved in both TAG-1 and axonin-1 using deoxyinosine at ambiguous positions. An expected 1000-bp fragment was obtained from cDNA derived from adult human cerebellum. Using this PCR fragment as a probe, several clones were isolated from a human fetal brain cDNA library. Nucleotide sequence analysis of a full-length clone, as expected, revealed a high degree of similarity to rat TAG-1 (91% identity) and chicken axonin-1 (75% identity) at the amino acid level. The encoded protein was then transiently expressed in monkey COS1 cells, and a stable mouse myeloma cell line was established expressing human TAG-1/axonin-1. The transfected COS1 and myeloma cells showed immunoreactivity on the cell surface with polyclonal anti-(chicken axonin-1) serum. On Western blots, the same antibodies recognized the recombinant protein migrating slightly slower on SDS/PAGE than chicken axonin-1. A comparison of chicken and human brain-tissue proteins by Western-blot analysis revealed a similar apparent molecular mass difference between the two species, which might be due to three additional N-glycosylation sites present on human TAG-1/axonin-1. Immunostaining of cryostat sections of embryonic retinas with polyclonal anti-(axonin-1) serum showed similar expression patterns in chicken and human samples at corresponding developmental stages. An additional shared feature of human TAG-1/axonin-1, rat TAG-1 and chick axonin-1 is their attachment to the cell membrane with a glycosyl-PtdIns anchor.

Amino Acid Sequence↗