Different types of adhesion at the Drosophila NMJ
Symbols are used consistently throughout; abbreviations: BM, basement membrane; ne, neuron; mf, myofilaments; mi, mitochondria; mu, muscle. A,B) Two examples of embryonic NMJs with active zones (black arrowheads), synaptic (between blue arrows) and extra-synaptic contacts (open arrowheads), and basement membrane (open arrow) overlaying the neuronal bouton. C) Magnified synaptic contact showing details of the dashed cleft material (between blue arrows). D) Cleft material displays honeycomb-like pattern in oblique sections. E) Loss of extra-synaptic adhesion in lanA mutant embryos (>>>). F) Structural details of synaptic contacts with intra-membraneous particles presynaptically (black arrow) and postsynaptically (orange arrow), coinciding with active zones and cleft material, respectively (>>>; >>>). G) Compartmentalisation of muscle surface (>>>): a) myoepidermal junction, b) focal hemiadherens junction, c) non-specialised basement membrane association, d) extra-synaptic contact, e) synaptic contact. The transcription factor Mef2 is crucial for NMJ adhesion (>>>) and could trigger (curved red arrows) either factors excluding Lan-receptors from NMJs (1) or factors mediating neuromuscular adhesion (2).