Clustering transmembrane-agrin induces filopodia-like processes on axons and dendrites

Annies, Maik; Bittcher, Godela; Ramseger, Rene; Löschinger, Jürgen; Wöll, Stefan; Porten, Elmar; Abraham, Christian; Rüegg, Markus A.; Kröger, Stephan

doi:10.1016/j.mcn.2005.11.005

Cited by 39 publications

(46 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In agreement with this hypothesis, it was recently shown that either clustering or overexpression of TM-agrin in neurons during the phase of active neurite extension reorganizes the actin cytoskeleton and induces the rapid formation of numerous filopodia-like processes extending from the primary neurite (21,22). In this study, we demonstrate that the TM-agrin-mediated formation of processes is the result of the initiation of an intracellular signaling cascade, which involves lipid rafts, the activation of the Src family kinase Fyn, and the activation of the mitogen-activated protein kinase (MAPK).…”

mentioning

confidence: 54%

“…TM-agrin is primarily expressed in the CNS on axons and dendrites during the phase of active neurite extension (15,21), and it has been hypothesized that neurite-associated TM-agrin might serve as a receptor or co-receptor (21). In agreement with this hypothesis, it was recently shown that either clustering or overexpression of TM-agrin in neurons during the phase of active neurite extension reorganizes the actin cytoskeleton and induces the rapid formation of numerous filopodia-like processes extending from the primary neurite (21,22).…”

Section: Association Of Tm-agrin With Lipid Rafts Results In the Phosmentioning

confidence: 99%

“…This antiserum was generated against the C-terminal half of agrin and, thus, specifically reacts with the extracellular part of all TM-agrin and NtA-agrin isoforms in Western blotting and immunohistochemistry. In contrast, sheep anti-TM-agrin (generated against a peptide of the intracellular domain of TM-agrin) reacts only with TM-agrin and not with NtA-agrin (21). Throughout this study, antiserum 46 was used to induce the filopodia-like processes.…”

Section: Methodsmentioning

confidence: 99%

“…Actin filaments were stained with Alexa488-conjugated phalloidin (Molecular Probes, Inc., Eugene, OR) (for details, see Ref. 21). Fluorescein-conjugated cholera toxin ␤-subunit was purchased from Sigma.…”

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Transmembrane Form Agrin-induced Process Formation Requires Lipid Rafts and the Activation of Fyn and MAPK

Ramseger

White

Kröger

2009

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

Overexpression or clustering of the transmembrane form of the extracellular matrix heparan sulfate proteoglycan agrin (TM-agrin) induces the formation of highly dynamic filopodialike processes on axons and dendrites from central and peripheral nervous system-derived neurons. Here we show that the formation of these processes is paralleled by a partitioning of TM-agrin into lipid rafts, that lipid rafts and transmembraneagrin colocalize on the processes, that extraction of lipid rafts with methyl-␤-cyclodextrin leads to a dose-dependent reduction of process formation, that inhibition of lipid raft synthesis prevents process formation, and that the continuous presence of lipid rafts is required for the maintenance of the processes. Association of TM-agrin with lipid rafts results in the phosphorylation and activation of the Src family kinase Fyn and subsequently in the phosphorylation and activation of MAPK. Inhibition of Fyn or MAPK activation inhibits process formation. These results demonstrate that the formation of filopodia-like processes by TM-agrin is the result of the activation of a complex intracellular signaling cascade, supporting the hypothesis that TM-agrin is a receptor or coreceptor on neurons.Agrin is a proteoglycan with a molecular mass of more than 500 kDa that is expressed in many tissues (for a review, see Ref. 1). Despite its widespread expression, the function of agrin is best characterized in skeletal muscle, where it is a key organizer during formation, maintenance, and regeneration of the neuromuscular junction (2, 3). Accordingly, mice with an inactivation of the agrn gene die at birth due to nonfunctional neuromuscular junctions and subsequent respiratory failure (4).Little is known about the role of agrin in other tissues, in particular in the central nervous system (for a review, see Ref. 5). Although neurons from mice with a targeted deletion of the agrn gene form synaptic specializations in vitro and in vivo (6, 7), the acute suppression of agrin expression or function by antisense probes or antibodies influences the formation and function of interneuronal synapses (8, 9). Likewise, brains of agrin-deficient mice, whose perinatal death was prevented by the reexpression of agrin specifically in motor neurons, have a severely reduced number of pre-and postsynaptic specializations at excitatory synapses (10). In addition, agrin isoforms are highly expressed by central nervous system neurons before synapse formation, suggesting additional functions for agrin during axonal and dendritic elongation (11-16). Although these data are consistent with a role of agrin during CNS 4 synaptogenesis, the precise role of agrin during CNS development remains to be clarified.Alternative first exon usage generates either a secreted soluble agrin molecule (NtA-agrin) or a transmembrane form of agrin (TM-agrin) (17, 18). The secreted form of agrin specifically interacts with the laminin ␥1-chain via its NtA-domain, resulting in a stable association with basal laminae (19,20). In contrast, in TM-agrin, t...

show abstract

mentioning

confidence: 54%

Section: Association Of Tm-agrin With Lipid Rafts Results In the Phosmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Transmembrane Form Agrin-induced Process Formation Requires Lipid Rafts and the Activation of Fyn and MAPK

Ramseger

White

Kröger

2009

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

show abstract

“…Functional studies provided additional evidence for a regulatory role of agrin on the rate of axonal and dendritic elongation in central neurons (Chang et al, 1997;Gautman et al, 1996;Ferreira, 1999;Mantych and Ferreira, 2001). This agrin effect was accompanied by clear changes in neuronal morphology including an enhanced branching pattern and the formation of filopodia-like processes protruding from axonal and dendritic shafts (Ferreira, 1999;Mantych and Ferreira, 2001;Annies et al, 2006;McCroskery et al, 2006). In this study, we showed that agrin also induced morphological changes in the growth cones of hippocampal neurons.…”

Section: Discussionmentioning

confidence: 55%

Agrin induced morphological and structural changes in growth cones of cultured hippocampal neurons

2007

View full text Add to dashboard Cite

The role of agrin in synaptogenesis has been extensively studied. On the other hand, little is known about the function of this extracellular matrix protein during developmental processes that precede the formation of synapses. Recently, it has been shown that agrin regulates the rate of neurite elongation and the behavior of growth cones in hippocampal and spinal neurons, respectively. However, the molecular mechanisms underlying these effects have not been completely elucidated.In the present study, we analyzed the morphological and molecular changes induced by agrin in growth cones of hippocampal neurons that developed in culture. Morphometric analysis showed a significant enlargement of growth cones of hippocampal neurons cultured in the presence of agrin. These agrin-induced growth cone changes were accompanied by the formation of loops of microtubules highly enriched in acetylated tubulin and an increase in the content of the microtubuleassociated protein MAP1B. Together, these data provide further insights into the potential molecular mechanisms underlying the effects of agrin on neurite outgrowth in central neurons.

show abstract

Retina development in zebrafish requires the heparan sulfate proteoglycan agrin

Liu¹,

Zhang²,

Kim

et al. 2008

Developmental Neurobiology

View full text Add to dashboard Cite

Recent studies from our laboratory have begun to elucidate the role of agrin in zebrafish development. One agrin morphant phenotype that results from agrin knockdown is microphthalmia (reduced eye size). To begin to understand the mechanisms underlying the role of agrin in eye development, we have analyzed retina development in agrin morphants. Retinal differentiation is impaired in agrin morphants, with retinal lamination being disrupted following agrin morpholino treatment. Pax 6.1 and Mbx1 gene expression, markers of eye development, are markedly reduced in agrin morphants. Formation of the optic fiber layer of the zebrafish retina is also impaired, exhibited as both reduced size of the optic fiber layer, and disruption of retinal ganglion cell axon growth to the optic tectum. The retinotectal topographic projection to the optic tectum is perturbed in agrin morphants in association with a marked loss of heparan sulfate expression in the retinotectal pathway, with this phenotype resembling retinotectal phenotypes observed in mutant zebrafish lacking enzymes for heparan sulfate synthesis. Treatment of agrin morphants with a fibroblast growth factor (Fgf) receptor inhibitor, rescue of the retinal lamination phenotype by transplantation of Fgf8-coated beads, and disruption of both the expression of Fgf-dependent genes and activation of ERK in agrin morphants provides evidence that agrin modulation of Fgf function contributes to retina development. Collectively, these agrin morphant phenotypes provide support for a crucial role of agrin in retina development and formation of an ordered retinotectal topographic map in the optic tectum of zebrafish.

show abstract

Clustering transmembrane-agrin induces filopodia-like processes on axons and dendrites

Cited by 39 publications

References 51 publications

Transmembrane Form Agrin-induced Process Formation Requires Lipid Rafts and the Activation of Fyn and MAPK

Transmembrane Form Agrin-induced Process Formation Requires Lipid Rafts and the Activation of Fyn and MAPK

Agrin induced morphological and structural changes in growth cones of cultured hippocampal neurons

Retina development in zebrafish requires the heparan sulfate proteoglycan agrin

Contact Info

Product

Resources

About