Figure 4. Electron microscopy (EM) shows that RIBEYE KO abolishes synaptic ribbons in retinal synapses formed by photoreceptor and bipolar cells.

1. Transmission EM demonstrates the absence of synaptic ribbons in presynaptic terminals of photoreceptor ribbon synapses in RBE ^KO/KO mice, while synaptic ribbons are readily visible in the terminals of RBE ^WT/WT mice. Asterisks in (A2) and (A3) denote photoreceptor active zones of RBE ^KO/KO mice in which the synaptic ribbon is absent. Except for the absence of synaptic ribbons, the ultrastructural appearance of the presynaptic terminals is comparable to that of RBE ^WT/WT mice. Abbreviations: sr, synaptic ribbon; pre, presynaptic; post, postsynaptic. Scale bars: 500 nm.
2. Transmission EM demonstrates the absence of synaptic ribbons in presynaptic terminals of bipolar cell ribbon synapses in RBE ^KO/KO mice, while synaptic ribbons are readily visible in the terminals of RBE ^WT/WT mice. Except for the absence of synaptic ribbons, the ultrastructural appearance of the presynaptic terminals is comparable to RBE ^WT/WT mice. Abbreviations are the same as in (A). Scale bars: 1 μm (B1, B2, B4, B5); 300 nm (B3, B6).