A major proportion of bead-induced presynapses is enriched in actin and concentrates more presynaptic components than non-enriched induced presynapses. (A) Widefield fluorescence image of cultured neurons 2 d after bead seeding at 8 div, labeled for actin (green), bassoon (purple), synapsin (orange), and map2 (gray). (B) Zooms corresponding to the areas highlighted in A: top row, actin-enriched induced presynapse at an axon-bead contact (A+); second row, induced presynapse at an axon-bead contact with no actin enrichment (A−); third row, axon-bead contact with no induced presynapse (S−); bottom row, natural synapse at axon-dendrite contact (NS). (C) Widefield fluorescence image of cultured neurons 2 d after bead seeding at 8 div, labeled for actin (green), synaptophysin (purple), vamp2 (orange), and map2 (gray). (D) Zooms corresponding to the A+, A−, S− axon-bead contacts and natural synapses (NS) highlighted in C. Scale bars in A and C: 20 µm; B and D: 2 µm. (E) Quantification of the proportion of A+ (dark blue), A− (blue), and S− (gray) axon-bead contacts. (F) Quantification of the labeling intensity for actin (green), bassoon (dark purple), synaptophysin (purple), synapsin (orange), and vamp2 (yellow) at actin-enriched presynapses (A+), induced presynapses with no actin enrichment (A−), and axon-bead contacts devoid of presynapse (S−), normalized to the intensity at A+ presynapses. Significance signs on graphs compare to the value for the same labeling in actin-enriched presynapses (A+, normalized to 1.0). See Data S1 file for detailed statistics.