Figure 2. Quantifications of ultrastructural NMJ phenotypes.

Embryonic NMJ boutons displaying active zones (arrows in Figs. 1, 4 and 5) were measured. Genotypes are grouped into combinations of cadherins and neurexins (A), Laminin-deficient conditions (B), combinations of lanA^9.32 with loss of cadherins (C), loss of other potential adhesion factors (as explained below) in combination with lanA^9.32 (D), loss of classical laminin receptors (E), and collagen type IV-deficient conditions (F). The following parameters were analysed: “adhesion index”, the percentage of the circumference of active zone-bearing boutons that is in contact with muscle membrane (between curved arrows in Figs. 1, 4 and 5); “synapse length”, mean length of electron dense cleft material known to indicate synapse diameter (between double chevrons in Figs. 1, 4 and 5); “cleft width”, mean distance between pre- and postsynaptic membranes at synapses. Bars represent mean ± standard error of the mean; n, number of assessed NMJ boutons sampled from at least 5 embryos, respectively; asterisks indicate statistical significances as compared to wt (black asterisks) or lanA (grey asterisks; *, P≤0.1; **, P≤0.01; ***, P≤0.001; ****, P≤0.0001 according to Mann Whitney tests). Additional information on included CAMs not explained in the main text: the immunoglobulin adhesion receptor Klingon is suggested to express potential synaptic functions [88], [89]; the immunoglobulin adhesion receptor Turtle acts as a homophilic adhesion factor in S2 cell assays which has demonstrated neuronal phenotypes in vivo [91], [92], [104], [105]; the transmembrane heparan sulfate proteoglycan Syndecan (Sdc) might act as a CAM by serving as a ligand for the motorneuronal receptor Lar (Leukocyte-antigen-related-like, a close homolog of avian protein tyrosin phosphatase ó) [106]–[108].