Spatial distribution and molecular dynamics of dystrophin glycoprotein components at the neuromuscular junction in vivo

Abstract

Bimolecular fluorescence complementation (BiFC) approach was used to study the molecular interactions between different components of the postsynaptic protein complex at the neuromuscular junction of living mice. Here, we showed that rapsyn forms complex with both α-dystrobrevin and α-syntrophin at the crests of junctional folds. The linkage of rapsyn to α-syntrophin and/or α-dystrobrevin is mediated by utrophin, a protein localized at AChR-rich domain. In mice deficient in α-syntrophin, in which utrophin is no longer present at the synapse, rapsyn interaction with α- dystrobrevin was completely abolished. This interaction was completely restored when either utrophin or α-syntrophin was introduced into muscles deficient in α-syntrophin. However, in NMJ deficient in α-dystrobrevin, in which utrophin remains intact, complex formation between rapsyn and α-syntrophin was not affected. Using fluorescence recovery after photobleaching, we found that α-syntrophin is turning over 5-7 times faster than AChRs and loss of α-dystrobrevin has no effect on rapsyn and α-syntrophin half-lives whereas the half-life of AChR is significantly altered. Altogether, these results provide new insights into the spatial distribution of dystrophin glycoprotein components and their dynamisms in living mice.