Distribution of agrin mRNAs in the chick embryo nervous system

Ma, Enbo; Morgan, R. Garret; Godfrey, EW

doi:10.1523/jneurosci.14-05-02943.1994

Cited by 62 publications

(64 citation statements)

References 26 publications

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“…In contrast to neurons, muscle cells express high levels of transcripts encoding agrinAoB0 Hoch et ai., 1993;Ma et al, 1994). In agreement with previous reports , we find that recombinant agrinA0so does not show any activity.…”

Section: Role Of Agrin Isoforms In the Formation Of The Neuromuscularsupporting

confidence: 93%

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Acetylcholine receptor-aggregating activity of agrin isoforms and mapping of the active site.

Gesemann

Denzer

Rüegg

1995

The Journal of Cell Biology

221

228

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Abstract. Agrin is a basal lamina protein that induces aggregation of acetylcholine receptors (AChRs) and other molecules at the developing neuromuscular junction. Alternative splicing of chick agrin mRNA at two sites, A and B, gives rise to eight possible isoforms of which five are expressed in vivo. Motor neurons express high levels of isoforms with inserts at sites A and B, muscle cells synthesize isoforms that lack amino acids at the B-site. To obtain further insights into the mechanism of agrin-induced AChR aggregation, we have determined the ECs0 (effective concentration to induce half-maximal AChR clustering) of each agrin isoform and of truncation mutants. On chick myotubes, ECs0 of the COOH-terminal, 95-kD fragment of agrinA4a8 was ,'~35 pM, of agrinA4aZ9 ~110 pM and of agrinA4a, --5 nM. While some AChR clusters were observed with 64 nM of agrinA4aO, no activity was detected for agrinAoa0. Recombinant fulllength chick agrin and a 100-kD fragment of ray agrin showed similar ECso values. A 45-kD, COOH-terminal fragment of agrinA4u retained high activity (ECso ----130 pM) and a 21-kD fragment was still active, but required higher concentrations (ECs0 ---13 nM). Unlike the 45-kD fragment, the 21-kD fragment neither bound to heparin nor did heparin inhibit its capability to induce AChR aggregation. These data show quantitatively that agrinA4nS and agrinA4mg, expressed in motor neurons, are most active, while no activity is detected in agrinAoBo, the dominant isoform synthesized by muscle cells. Furthermore, our results show that a fragment comprising site Bs and the most COOHterminal G-like domain is sufficient for this activity, and that agrin domains required for binding to heparin and those for AChR aggregation are distinct from each other.T HE formation of chemical synapses in the nervous system requires exchange of local signals between preand postsynaptic cells. At the neuromuscular junction (NMJ) ~, muscle cells aggregate several proteins, such as acetylcholine receptors (AChRs), acetylcholinesterase, and heparan sulfate proteoglycans at the site of contact between nerve and muscle cell. This process is, at least in part, initiated by the release of molecules from the motor axon. Several lines of evidence suggest that agrin, a component of synaptic basal lamina, is such a molecule. On cultured myotubes, agrin induces aggregation of several molecules that are concentrated at the NMJ including AChRs (Nitkin et al., 1987;Wallace, 1989). Motor neurons synthesize agrin, transport it to the nerve terminal from where it is released to induce AChR aggregation (Magill

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Section: Role Of Agrin Isoforms In the Formation Of The Neuromuscularsupporting

confidence: 93%

“…Thus, cholinergic neurons express a mixture of agrin isoforms and depending on the developmental stage, agrin^4,s or agrin^,B19 is most abundant. Nonneuronal and muscle ceils, on the other hand, express only mRNA encoding agrin^4B0 and agrinmB0 Hoch et al, 1993;Ma et al, 1994;Smith and O'Dowd, 1994).…”

mentioning

confidence: 99%

Acetylcholine receptor-aggregating activity of agrin isoforms and mapping of the active site.

Gesemann

Denzer

Rüegg

1995

The Journal of Cell Biology

221

228

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“…The agrin A4B8 isoform used in this study is abundantly expressed by chick and rat motor neurons Smith and O'Dowd, 1994;Ma et al, 1994;Stone and Nikolics, 1995). Our experiments demonstrate that ectopic neural agrin can induce ectopic AChR clusters in vivo.…”

Section: Discussionmentioning

confidence: 56%

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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“…This raises the intriguing possibility that these active agrin isoforms (B8 and BI9 ) were specifically ex- cell layer in both chick and rat cerebellum [20,21]. It remains to be determined that this labeling comes from Bs or B,9 agrin isoforms.…”

Section: Discussionmentioning

confidence: 99%

Cerebellar granule cells express a specific isoform of agrin that lacks the acetylcholine receptor aggregating activity

Pun

Wan

et al. 1996

FEBS Letters

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Distribution of agrin mRNAs in the chick embryo nervous system

Cited by 62 publications

References 26 publications

Acetylcholine receptor-aggregating activity of agrin isoforms and mapping of the active site.

Acetylcholine receptor-aggregating activity of agrin isoforms and mapping of the active site.

Neural Agrin Induces Ectopic Postsynaptic Specializations in Innervated Muscle Fibers

Cerebellar granule cells express a specific isoform of agrin that lacks the acetylcholine receptor aggregating activity

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