Ribbon synapses reliably transmit synaptic signals over a broad signalling range. Rod
photoreceptor ribbon synapses are capable of transmitting signals generated by the absorption of
single photons. The high precision of ribbon synapses emphasizes the need for particularly efficient
signalling mechanisms. Synaptic ribbons are presynaptic specializations of ribbon synapses and are
anchored to the active zone. Synaptic ribbons bind many synaptic vesicles that are delivered to the
active zone for continuous and faithful signalling. In the present study we demonstrate with independent antibodies at the light- and electron microscopic level that rabconnectin-3α (RC3α)—alternative
name Dmx-like 2 (DMXL2)—is localized to the synaptic ribbons of rod photoreceptor synapses in
the mouse retina. In the brain, RC3α-containing complexes are known to interact with important
components of synaptic vesicles, including Rab3-activating/inactivating enzymes, priming proteins
and the vesicular H+
-ATPase that acidifies the synaptic vesicle lumen to promote full neurotransmitter loading. The association of RC3α/DMXL2 with rod synaptic ribbons of the mouse retina could
enable these structures to deliver only fully signalling-competent synaptic vesicles to the active zone
thus contributing to reliable synaptic communication