Fig. 8

BCs form ribbon-containing and ribbon-free contacts with wild-type RGCs. a (Top panels) Relationship of PSD95-YFP puncta on ON-alpha RGCs (blue) with ribbons (CtBP2 labeling) at P9 and P32. Contact sites with PSD95-YFP and CtBP2 apposed are indicated as ‘colocalized’ (magenta) whereas PSD95-YFP sites without CtBP2 are marked as ‘non-colocalized’ (yellow). (Bottom panels) Magnified views of the stretch of dendrite within the rectangles. Red arrows indicate PSDS95 puncta not apposed to CtBP2 puncta. b Developmental increase of PSD95 density on the dendrites of ON-alpha RGCs. c Percentage of CtBP2 puncta apposed to PSD95 puncta on the dendrites of ON-alpha RGCs across development. N = 4–6 cells from 3–6 retinas. d Maximum intensity projections of confocal image stacks of en face views of T6 BC axon terminals and the dendrites and PSD95 puncta of an ON-alpha RGC. Two example synaptic contacts are marked with the asterisks. Magnified views for both contacts are shown on the right. (1) ribbon synaptic contact; (2) ribbonless synaptic contact. e Electron micrograph showing a typical ribbon (arrowhead) synapse between a T6 BC axon and a dyad of ON-alpha RGC and amacrine cell (AC) dendrites. Both GC and amacrine cell membranes are line with PSDs (brackets). f Two consecutive electron micrographs (S129 and S130) showing a non-ribbon contact (arrows) for the same T6 BC and ON-alpha GC pair shown in e. The GC membrane is slightly concave and clearly lined by a postsynaptic density (brackets). Data are presented as mean ± sem