Topic: photoreceptor ribbon synapses

The large, homologous proteins Bassoon (Bsn) and Piccolo are part of the cytomatrix at the active zone (AZ) of conventional chemical synapses, where they can partially compensate for each other’s function. At the highly specialized photoreceptor ribbon synapses, Piccolino (Pclo), a C-terminally truncated splice variant of Piccolo, is the functional partner of Bsn. In earlier studies, we detected free-floating photoreceptor synaptic ribbons and disrupted AZs in Bsn single knockout (sKO) mice1 and a loss of the plate‑like ribbon structure, but attached photoreceptor synaptic ribbons, in Pclo sKO

Synaptic ribbons (SRs) are the presynaptic hallmark of sensory ribbon synapses. SRs tether up to several hundred synaptic vesicles (SVs) to support continuous exocytosis. How tethering of SVs to SRs is achieved is currently unknown. We previously demonstrated that Piccolino, an integral component of SRs1,2, binds to RIBEYE, the main component of SRs, via its C-terminus3. Here, we explore how the N-terminus of Piccolino might interact with SVs. First, we ultrastructurally analyzed the distribution of SVs at photoreceptor ribbon synapses in Piccolino knock-out (KO) mice. We found a decrease in t