Time Lapse in Vivo Visualization of Developmental Stabilization of Synaptic Receptors at Neuromuscular Junctions

Pessah Yampolsky,Pier Giorgio Pacifici,Lukas Lomb,Günter Giese,Rüdiger Rudolf,Ira V Röder,Veit Witzemann

doi:10.1074/jbc.m110.168880

Abstract

The lifetime of nicotinic acetylcholine receptors (AChRs) in neuromuscular junctions (NMJs) is increased from <1 day to >1 week during early postnatal development. However, the exact timing of AChR stabilization is not known, and its correlation to the concurrent embryonic to adult AChR channel conversion, NMJ remodeling, and neuromuscular diseases is unclear. Using a novel time lapse in vivo imaging technology we show that replacement of the entire receptor population of an individual NMJ occurs end plate-specifically within hours. This makes it possible to follow directly in live animals changing stabilities of end plate receptors. In three different, genetically modified mouse models we demonstrate that the metabolic half-life values of synaptic AChRs increase from a few hours to several days after postnatal day 6. Developmental stabilization is independent of receptor subtype and apparently regulated by an intrinsic muscle-specific maturation program. Myosin Va, an F-actin-dependent motor protein, is also accumulated synaptically during postnatal development and thus could mediate the stabilization of end plate AChR.

Highlights

In the adult synapses the acetylcholine receptors (AChRs) turnover is rather slow (t1⁄2 Ϸ 10 days) [1, 7,8,9,10]
In the current study we implemented in vivo time lapse imaging techniques for direct, continuous visualization of surface AChR trafficking in vivo
Time Lapse in Vivo Imaging at Early Postnatal Stages—Our aim was to resolve in vivo changes in AChR stability and changes of receptor composition in individual neuromuscular junctions (NMJs)

Summary

Introduction

In the adult synapses the AChRs turnover is rather slow (t1⁄2 Ϸ 10 days) [1, 7,8,9,10]. Using nonsaturating r-bgt concentrations for end plate is significantly lower than the AChR⑀ content (75.8 Ϯ 3.8%) in staining, we measured the apparent metabolic stability of the end plates of AChR␥-GFP/␥-GFP animals on the same postnatal

Objectives

Results

Conclusion