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A functional role for specific spliced variants of the alpha7beta1 integrin in acetylcholine receptor clustering.

Burkin DJ, Gu M, Hodges BL, Campanelli JT, Kaufman SJ - J. Cell Biol. (1998)

Bottom Line: High concentrations of anti-alpha7 antibodies inhibit colocalization of the integrin with AChR clusters as well as the enhanced response promoted by both laminin and agrin.Whereas both the alpha7A and alpha7B cytoplasmic domain variants cluster with AChR, only those isoforms containing the alpha7X2 extracellular domain were active.These results demonstrate that the alpha7beta1 integrin has a physiologic role in laminin-induced AChR clustering, that alternative splicing is integral to this function of the alpha7 chain, and that laminin, agrin, and the alpha7beta1 integrin interact in a common or convergent pathway in the formation of neuromuscular junctions.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801, USA.

ABSTRACT
The clustering of acetylcholine receptors (AChR) on skeletal muscle fibers is an early event in the formation of neuromuscular junctions. Recent studies show that laminin as well as agrin can induce AChR clustering. Since the alpha7beta1 integrin is a major laminin receptor in skeletal muscle, we determined if this integrin participates in laminin and/or agrin-induced AChR clustering. The alternative cytoplasmic domain variants, alpha7A and alpha7B, and the extracellular spliced forms, alpha7X1 and alpha7X2, were studied for their ability to engage in AChR clustering. Immunofluorescence microscopy of C2C12 myofibers shows that the alpha7beta1 integrin colocalizes with laminin-induced AChR clusters and to a much lesser extent with agrin-induced AChR clusters. However, together laminin and agrin promote a synergistic response and all AChR colocalize with the integrin. Laminin also induces the physical association of the integrin and AChR. High concentrations of anti-alpha7 antibodies inhibit colocalization of the integrin with AChR clusters as well as the enhanced response promoted by both laminin and agrin. Engaging the integrin with low concentrations of anti-alpha7 antibody initiates cluster formation in the absence of agrin or laminin. Whereas both the alpha7A and alpha7B cytoplasmic domain variants cluster with AChR, only those isoforms containing the alpha7X2 extracellular domain were active. These results demonstrate that the alpha7beta1 integrin has a physiologic role in laminin-induced AChR clustering, that alternative splicing is integral to this function of the alpha7 chain, and that laminin, agrin, and the alpha7beta1 integrin interact in a common or convergent pathway in the formation of neuromuscular junctions.

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Immunofluorescence localization of the β1 (green) integrin at  AChR clusters (red). Anti-β1 mAb is  colocalized at 82% (n = 91) of agrin- induced and 92% (n = 145) of laminin-induced AChR clusters. Bar, 15 μm.
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Figure 7: Immunofluorescence localization of the β1 (green) integrin at AChR clusters (red). Anti-β1 mAb is colocalized at 82% (n = 91) of agrin- induced and 92% (n = 145) of laminin-induced AChR clusters. Bar, 15 μm.

Mentions: To confirm the localization of β1 integrins at AChR clusters, an additional anti-β1 integrin mAb was used. As seen in Fig. 7, the integrin β1 chain was localized to both agrin and laminin-induced AChR clusters. The β1 integrin colocalized with ∼82% of agrin-induced clusters and 92% of laminin-induced clusters. This result is consistent with the inhibition of agrin-induced clustering by anti-β1 antibody and the role of the αvβ1 integrin in this process (Martin and Sanes, 1997). The β1 integrin has also been localized at agrin-induced AChR clusters in chick myofibers (Bozyczko et al., 1989).


A functional role for specific spliced variants of the alpha7beta1 integrin in acetylcholine receptor clustering.

Burkin DJ, Gu M, Hodges BL, Campanelli JT, Kaufman SJ - J. Cell Biol. (1998)

Immunofluorescence localization of the β1 (green) integrin at  AChR clusters (red). Anti-β1 mAb is  colocalized at 82% (n = 91) of agrin- induced and 92% (n = 145) of laminin-induced AChR clusters. Bar, 15 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132957&req=5

Figure 7: Immunofluorescence localization of the β1 (green) integrin at AChR clusters (red). Anti-β1 mAb is colocalized at 82% (n = 91) of agrin- induced and 92% (n = 145) of laminin-induced AChR clusters. Bar, 15 μm.
Mentions: To confirm the localization of β1 integrins at AChR clusters, an additional anti-β1 integrin mAb was used. As seen in Fig. 7, the integrin β1 chain was localized to both agrin and laminin-induced AChR clusters. The β1 integrin colocalized with ∼82% of agrin-induced clusters and 92% of laminin-induced clusters. This result is consistent with the inhibition of agrin-induced clustering by anti-β1 antibody and the role of the αvβ1 integrin in this process (Martin and Sanes, 1997). The β1 integrin has also been localized at agrin-induced AChR clusters in chick myofibers (Bozyczko et al., 1989).

Bottom Line: High concentrations of anti-alpha7 antibodies inhibit colocalization of the integrin with AChR clusters as well as the enhanced response promoted by both laminin and agrin.Whereas both the alpha7A and alpha7B cytoplasmic domain variants cluster with AChR, only those isoforms containing the alpha7X2 extracellular domain were active.These results demonstrate that the alpha7beta1 integrin has a physiologic role in laminin-induced AChR clustering, that alternative splicing is integral to this function of the alpha7 chain, and that laminin, agrin, and the alpha7beta1 integrin interact in a common or convergent pathway in the formation of neuromuscular junctions.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801, USA.

ABSTRACT
The clustering of acetylcholine receptors (AChR) on skeletal muscle fibers is an early event in the formation of neuromuscular junctions. Recent studies show that laminin as well as agrin can induce AChR clustering. Since the alpha7beta1 integrin is a major laminin receptor in skeletal muscle, we determined if this integrin participates in laminin and/or agrin-induced AChR clustering. The alternative cytoplasmic domain variants, alpha7A and alpha7B, and the extracellular spliced forms, alpha7X1 and alpha7X2, were studied for their ability to engage in AChR clustering. Immunofluorescence microscopy of C2C12 myofibers shows that the alpha7beta1 integrin colocalizes with laminin-induced AChR clusters and to a much lesser extent with agrin-induced AChR clusters. However, together laminin and agrin promote a synergistic response and all AChR colocalize with the integrin. Laminin also induces the physical association of the integrin and AChR. High concentrations of anti-alpha7 antibodies inhibit colocalization of the integrin with AChR clusters as well as the enhanced response promoted by both laminin and agrin. Engaging the integrin with low concentrations of anti-alpha7 antibody initiates cluster formation in the absence of agrin or laminin. Whereas both the alpha7A and alpha7B cytoplasmic domain variants cluster with AChR, only those isoforms containing the alpha7X2 extracellular domain were active. These results demonstrate that the alpha7beta1 integrin has a physiologic role in laminin-induced AChR clustering, that alternative splicing is integral to this function of the alpha7 chain, and that laminin, agrin, and the alpha7beta1 integrin interact in a common or convergent pathway in the formation of neuromuscular junctions.

Show MeSH
Related in: MedlinePlus