The ability of agrin to cluster AChRs depends on alternative splicing and on cell surface proteoglycans

Ferns, Michael J.; Campanelli, James T.; Hoch, Werner; Scheller, Richard H.; Hall, Zach W.

doi:10.1016/0896-6273(93)90153-i

Cited by 294 publications

(250 citation statements)

References 36 publications

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“…Splicing isoforms containing 0 or 4 amino acid inserts at the y splicing site of the LG2 domain and 0, 8, 11, or 19 (8 + 11) amino acid inserts at the z splicing site of the LG3 domain of the C‐terminus have been investigated ( Figure 1). 23, 40 The neural agrin containing 4 and 8 amino acid inserts at the y and z sites, respectively, has a high affinity to the AChR clustering, while muscle agrin and agrin found in other non‐neuronal cells lacks inserts and fails to cluster AChRs 41. However, splicing isoforms of agrin lacking inserts have been found in NMJs (motor neurons, skeletal muscle, and Schwann cells), in the central nervous system and peripheral tissues (lung and kidney) 23.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation

Scherbakov

Knops

Ebner³

et al. 2015

Journal of Cachexia, Sarcopenia and Muscle

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BackgroundC‐terminal Agrin Fragment (CAF) has been proposed as a novel biomarker for sarcopenia originating from the degeneration of the neuromuscular junctions. In patients with stroke muscle wasting is a common observation that predicts functional outcome. We aimed to evaluate agrin sub‐fragment CAF22 as a marker of decreased muscle mass and physical performance in the early phase after acute stroke.MethodsPatients with acute ischaemic or haemorrhagic stroke (n = 123, mean age 70 ± 11 y, body mass index BMI 27.0 ± 4.9 kg/m2) admitted to inpatient rehabilitation were studied in comparison to 26 healthy controls of similar age and BMI. Functional assessments were performed at begin (23 ± 17 days post stroke) and at the end of the structured rehabilitation programme (49 ± 18 days post stroke) that included physical assessment, maximum hand grip strength, Rivermead motor assessment, and Barthel index. Body composition was assessed by bioelectrical impedance analysis (BIA). Serum levels of CAF22 were measured by ELISA.ResultsCAF22 levels were elevated in stroke patients at admission (134.3 ± 52.3 pM) and showed incomplete recovery until discharge (118.2 ± 42.7 pM) compared to healthy controls (95.7 ± 31.8 pM, p < 0.001). Simple regression analyses revealed an association between CAF22 levels and parameters of physical performance, hand grip strength, and phase angle, a BIA derived measure of the muscle cellular integrity. Improvement of the handgrip strength of the paretic arm during rehabilitation was independently related to the recovery of CAF22 serum levels only in those patients who showed increased lean mass during the rehabilitation.ConclusionsCAF22 serum profiles showed a dynamic elevation and recovery in the subacute phase after acute stroke. Further studies are needed to explore the potential of CAF22 as a serum marker to monitor the muscle status in patients after stroke.

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Section: Discussionmentioning

confidence: 99%

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation

Scherbakov

Knops

Ebner³

et al. 2015

Journal of Cachexia, Sarcopenia and Muscle

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“…PCR products were radiolabeled by inclusion of ϳ2 ϫ 10 5 cpm of 32 P-labeled forward primer in the reaction mixture, separated by electrophoresis on 8% polyacrylamide gels, and the relative abundance determined by analysis of the gel with a PhosphorImager (Molecular Dynamics, Sunnyvale, CA). To investigate the pattern of alternative splicing at either the Y or Z sites, samples were subjected to a single round of amplification (35 cycles) using oligonucleotide primers F111/ B112 or F24/B2 flanking the Y and Z sites, respectively (18,19). To examine alternative splicing in the Z region of agrin transcripts containing the 4-amino acid insert at the Y site, two rounds of amplification were performed using nested primers.…”

Section: Methodsmentioning

confidence: 99%

“…Optional exclusion of sequences encoding 4 amino acids at the Y site and 8 and 11 amino acids at the Z site result in mRNAs encoding agrin proteins with unique functional properties and tissue-specific patterns of expression. For example, forms of agrin lacking inserts at the both Y and Z sites (agrin y0z0 ) are unable to induce clustering of AChR (7,19) and are most highly expressed by non-neuronal cells (7,8). In contrast, agrin proteins containing the 4-amino acid insert at the Y site and either one or both of the 8 and 11 amino acid inserts at the Z site (agrin y4z8 , agrin y4z11 , and agrin y4z19 ) are potent inducers of AChR aggregates (7,19) and are specifically expressed by neurons (7,8).…”

mentioning

confidence: 99%

Selective Regulation of Agrin mRNA Induction and Alternative Splicing in PC12 Cells by Ras-dependent Actions of Nerve Growth Factor

Smith¹,

Fanger²,

O'Connor³

et al. 1997

Journal of Biological Chemistry

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The extracellular matrix protein agrin plays an important role in the formation and maintenance of the neuromuscular junction. However, regulation of agrin gene expression and pre-mRNA splicing, important in determining the biological actions of agrin, is not well understood. To begin to identify mechanisms controlling agrin expression, quantitative polymerase chain reaction techniques were used to analyze the effect of growth factors on the expression of agrin mRNA isoforms in rat pheochromocytoma (PC12) cells. Agrin transcripts in untreated cells lacked inserts in the Y and Z sites (agrin y0z0 ), encoding agrin isoforms with low acetylcholine receptor aggregating activity and a primarily non-neuronal tissue distribution. Transcripts encoding isoforms with high aggregating activity and neuronal tissue distribution (agrin y4z8 , agrin y4z11 , and agrin y4z19 ) were not detected. Treatment of PC12 cells with nerve growth factor (NGF) caused a significant increase in total agrin mRNA. In contrast, exposure to epidermal growth factor had no effect. Analysis of alternative splicing of agrin mRNA revealed that NGF elicited a specific increase in agrin y4 and agrin z8 mRNAs that did not occur in the presence of epidermal growth factor, insulin, dexamethasone, or retinoic acid. Analysis of PC12 sublines stably overexpressing a dominant inhibitory form of p21 Ras indicated that NGF induced changes in levels of agrin mRNA and alternative splicing required Ras activity. The results show that NGF can influence important aspects of neuronal differentiation by regulating alternative splicing. Furthermore, these data provide insight into the mechanisms governing agrin gene expression and suggest that neurotrophic factors may play a role in regulating agrin expression in vivo.

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“…However, when presented in a cell-attached form, rat agrin lacking inserts at sites A and B was shown to have some AChR-aggregating activity (C ampanelli et al, 1991;Ferns et al, 1992Ferns et al, , 1993. To address whether the agrin A0B0 isoform, when expressed in a physiological context, would have such aggregating activity, we also injected cDNA constructs encoding cAgrin 7A0B0 into extrasynaptic fiber regions.…”

Section: Induction Of Postsynaptic Specializations In Vivo Is Splice-mentioning

confidence: 99%

Neural Agrin Induces Ectopic Postsynaptic Specializations in Innervated Muscle Fibers

Meier¹,

et al. 1997

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Neural agrin, in the absence of a nerve terminal, can induce the activity-resistant expression of acetylcholine receptor (AChR) subunit genes and the clustering of synapse-specific adult-type AChR channels in nonsynaptic regions of adult skeletal muscle fibers. Here we show that, when expression plasmids for neural agrin are injected into the extrasynaptic region of innervated muscle fibers, the following components of the postsynaptic apparatus are aggregated and colocalized with ectopic agrininduced AChR clusters: laminin-␤2, MuSK, phosphotyrosinecontaining proteins, ␤-dystroglycan, utrophin, and rapsyn. These components have been implicated to play a role in the differentiation of neuromuscular junctions. Furthermore, ErbB2 and ErbB3, which are thought to be involved in the regulation of neurally induced AChR subunit gene expression, were colocalized with agrin-induced AChR aggregates at ectopic nerve-free sites. The postsynaptic muscle membrane also contained a high concentration of voltage-gated Na ϩ channels as well as deep, basal lamina-containing invaginations comparable to the secondary synaptic folds of normal endplates. The ability to induce AChR aggregation in vivo was not observed in experiments with a muscle-specific agrin isoform. Thus, a motor neuron-specific agrin isoform is sufficient to induce a full ectopic postsynaptic apparatus in muscle fibers kept electrically active at their original endplate sites.

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The ability of agrin to cluster AChRs depends on alternative splicing and on cell surface proteoglycans

Cited by 294 publications

References 36 publications

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation

Selective Regulation of Agrin mRNA Induction and Alternative Splicing in PC12 Cells by Ras-dependent Actions of Nerve Growth Factor

Neural Agrin Induces Ectopic Postsynaptic Specializations in Innervated Muscle Fibers

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