Microinjection of a monoclonal antibody against a 37-kD protein (tropomyosin 2) prevents the formation of new acetylcholine receptor clusters.

Marazzi, Giovanna; Bard, Frédérique; Klymkowsky, Michael W.; Rubin, Lee L.

doi:10.1083/jcb.109.5.2337

Cited by 11 publications

(6 citation statements)

References 28 publications

(26 reference statements)

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“…This hypothesis is consistent with our observations that agrin-induced aggregation of AChRs utilizes AChRs already in the myotube membrane and requires metabolic energy but not protein synthesis. It is also consistent with the evidence that AChR immobilization is mediated by attachment to the cytoskeleton (Bloch 1986;Froehner 1986;Anthony et al 1988;Bloch & Morrow 1989;Marazzi et al 1989), and with photobleach-recovery measurements that indicate that not only are AChRs in agrin-induced aggregates immobile, but agrin also immobilizes a fraction of the receptors in the diffuse phase (Dubinsky et al 1989). Interestingly, attachment of AChRs to the cytoskeleton is thought to occur through an interaction of the P subunit with the 43 kD AChR-associated protein and actin filaments (Burden et al 1983;Walker et al 1984;Froehner 1986), and it is the P subunit that is phosphorylated by agrin.…”

Section: Agrin Hypothesissupporting

confidence: 91%

The mechanism of agrin-induced acetylcholine receptor aggregation

Wallace

1991

Phil. Trans. R. Soc. Lond. B

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Abstract. Agrin, a protein extracted from the electric organ of Torpedo californica, induces the formation of specializations on cultured chick myotubes that resemble the postsynaptic apparatus at the neuromuscular junction. The aim of the studies reported here was to characterize the effects of agrin on the distribution of acetylcholine receptors (AChRs) and cholinesterase as a step toward determining agrin's mechanism of action. When agrin was added to the medium bathing chick myotubes small (<4 ~tm 2) aggregates of AChRs began to appear within 2 h and increased rapidly in number until 4 h. Over the next 12-20 h the number of aggregates per myotube decreased as the mean size of each aggregate increased to •15 ttm 2. The accumulation of AChRs into agrin-induced aggregates occurred primarily by lateral migration of AChRs already in the myotube plasma membrane at the time agrin was added to the cultures. Aggregates of AChRs and cholinesterase remained as long as agrin was present in the medium; if agrin was removed the number of aggregates declined slowly. The formation and maintenance of agrin-induced AChR aggregates required Ca ++. Co ++ and Mn ÷÷ inhibited agrin-induced AChR aggregation and increased the rate of aggregate dispersal. Mg +÷ and Sr ÷+ could not substitute for Ca ÷+. Agrin-induced receptor aggregation also was inhibited by phorbol 12-myristate 13-acetate, an activator of protein kinase C, and by inhibitors of energy metabolism. The similarities between agrin's effects on cultured myotubes and events that occur during formation of neuromuscular junctions support the hypothesis that axon terminals release molecules similar to agrin that induce the differentiation of the postsynaptic apparatus.

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Section: Agrin Hypothesissupporting

confidence: 91%

The mechanism of agrin-induced acetylcholine receptor aggregation

Wallace

1991

Phil. Trans. R. Soc. Lond. B

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“…Rubin and co-workers (211) have demonstrated the existence of a specific Tm associated with acetylcholine receptor clusters (211) in cultured chick muscle cells. They similarly detected a cytoskeletal Tm associated with the rat neuromuscular junction (211). The precise identity of this Tm isoform has yet to be unambiguously identified.…”

Section: Skeletal Musclementioning

confidence: 99%

Tropomyosin-Based Regulation of the Actin Cytoskeleton in Time and Space

Gunning

O’Neill²,

Hardeman³

2008

Physiological Reviews

421

457

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Tropomyosins are rodlike coiled coil dimers that form continuous polymers along the major groove of most actin filaments. In striated muscle, tropomyosin regulates the actin-myosin interaction and, hence, contraction of muscle. Tropomyosin also contributes to most, if not all, functions of the actin cytoskeleton, and its role is essential for the viability of a wide range of organisms. The ability of tropomyosin to contribute to the many functions of the actin cytoskeleton is related to the temporal and spatial regulation of expression of tropomyosin isoforms. Qualitative and quantitative changes in tropomyosin isoform expression accompany morphogenesis in a range of cell types. The isoforms are segregated to different intracellular pools of actin filaments and confer different properties to these filaments. Mutations in tropomyosins are directly involved in cardiac and skeletal muscle diseases. Alterations in tropomyosin expression directly contribute to the growth and spread of cancer. The functional specificity of tropomyosins is related to the collaborative interactions of the isoforms with different actin binding proteins such as cofilin, gelsolin, Arp 2/3, myosin, caldesmon, and tropomodulin. It is proposed that local changes in signaling activity may be sufficient to drive the assembly of isoform-specific complexes at different intracellular sites.

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“…Biochemical analyses demonstrated that the infected myotubes were missing a 37-kD protein immunologically related to tropomyosin (1). An mAb to this protein, called tropomyosin 2, stained uninfected myotubes diffusely (1), and when injected into cells blocked the formation ofnew clusters, but did not disrupt preexisting clusters (50) . The blocking action of the antibody may be because of interference with specific interactions that occur locally at the AChR cluster between tropomyosin 2 and other cluster-associated proteins.…”

Section: Froehner Neuromuscular Postsynaptic Cytoskeletonmentioning

confidence: 99%