Cell Types and Synapses Expressing the SNARE Complex Regulating Proteins Complexin 1 and Complexin 2 in Mammalian Retina

Abstract

Complexins (Cplxs) 1 to 4 are components of the presynaptic compartment of chemical synapses where they regulate important steps in synaptic vesicle exocytosis. In the retina, all four Cplxs are present, and while we know a lot about Cplxs 3 and 4, little is known about Cplxs 1 and 2. Here, we performed in situ hybridization experiments and bioinformatics and exploited Cplx 1 and Cplx 2 single-knockout mice combined with immunocytochemistry and light microscopy to characterize in detail the cell type and synapse-specific distribution of Cplx 1 and Cplx 2. We found that Cplx 2 and not Cplx 1 is the main isoform expressed in normal and displaced amacrine cells and ganglion cells in mouse retinae and that amacrine cells seem to operate with a single Cplx isoform at their conventional chemical synapses. Surprising was the finding that retinal function, determined with electroretinographic recordings, was altered in Cplx 1 but not Cplx 2 single-knockout mice. In summary, the results provide an important basis for future studies on the function of Cplxs 1 and 2 in the processing of visual signals in the mammalian retina.

Light-dependent regulation of neurotransmitter release from rod photoreceptor ribbon synapses involves an interplay of Complexin 4 and Transducin with the SNARE complex

“…In mouse retina, all four known Complexin (Cplx) isoforms, Cplx1-Cplx4, are present. While Cplx1 and Cplx2 are found at conventional chemical synapses in the retina, photoreceptor ribbon synapses are equipped with Cplx3 and Cplx4 ( Reim et al, 2005 ; Lux et al, 2021 ). We showed previously for the cone photoreceptor ribbon synapse in mouse retina that (i) Cplx3 and Cplx4 suppress tonic and facilitate evoked transmitter release, (ii) loss of Cplx3 and Cplx4 perturbs ribbon synapse function and differentially impacts ON and OFF pathways of the retina ( Reim et al, 2009 ; Landgraf et al, 2012 ; Babai et al, 2016 ), and (iii) Cplx3 and Cplx4 co-regulate the light-dependent replenishment of SVs to the synaptic ribbon of cone photoreceptors ( Babai et al, 2016 ).…”