Live imaging of neuromuscular junctions (NMJs) in situ has been constrained by the suitability of ligands for inert vital staining of motor nerve terminals. Here, we constructed several truncated derivatives of the tetanus toxin C-fragment (TetC) fused with Emerald Fluorescent Protein (emGFP). Four constructs, namely full length emGFP-TetC (emGFP-865:TetC) or truncations comprising amino acids 1066–1315 (emGFP-1066:TetC), 1093–1315 (emGFP-1093:TetC) and 1109–1315 (emGFP-1109:TetC), produced selective, high-contrast staining of motor nerve terminals in rodent or human muscle explants. Isometric tension and intracellular recordings of endplate potentials from mouse muscles indicated that neither full-length nor truncated emGFP-TetC constructs significantly impaired NMJ function or transmission. Motor nerve terminals stained with emGFP-TetC constructs were readily visualised in situ or in isolated preparations using fibre-optic confocal endomicroscopy (CEM). emGFP-TetC derivatives and CEM also visualised regenerated NMJs. Dual-waveband CEM imaging of preparations co-stained with fluorescent emGFP-TetC constructs and Alexa647-α-bungarotoxin resolved innervated from denervated NMJs in axotomized WldS mouse muscle and degenerating NMJs in transgenic SOD1G93A mouse muscle. Our findings highlight the region of the TetC fragment required for selective binding and visualisation of motor nerve terminals and show that fluorescent derivatives of TetC are suitable for in situ morphological and physiological characterisation of healthy, injured and diseased NMJs.
|Publication status||Published - Oct 2021|
Bibliographical noteFunding Information:
Funding: This research was principally funded by the Motor Neurone Disease Association (UK), grant number 838-791, and by the Medical Research Council (MRC), grant number MR/M024075. Additional support was obtained from the Biotechnology and Biological Research Council (BBSRC), grant numbers BBS/E/D/10002071 and BB/P007996/1; the Engineering and Physical Sciences Research Council (EPSRC) grants EP/R00661X/1, EP/S019367/1, EP/P02470X/1 and EP/P025285/1; and the Wellcome Trust, 208339/Z/17/Z.
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- Neuromuscular junction
- Tetanus toxin