Abstract
Purpose :
Cell adhesion molecules (CAMs) have an important role in synapse formation in the retina. Nectins and nectin-like molecules (Necls) are immunoglobulin-like CAMs that are essential for cell-cell adhesion in the central nervous system (CNS). Among them, Necl-1/CADM3 is expressed at the contact sites between axons and glial processes and is essential for the myelination of the CNS and the peripheral nervous system. Necl-1 is also expressed in the photoreceptors and bipolar cells of the zebra fish retina, However, the localization or function of Necl-1 has not been investigated in the murine retina. We studied here these issues.
Methods :
We generated Necl-1 knockout (Necl-1 (-/-)) mice and crossed them with pure C57BL/6J mice more than 10 times. All experiments were performed using Necl-1 (-/-) mice and their wild-type littermates at age of 8 to 12 weeks. We analyzed the localization of Necl-1 in the retina using immunohistochemistry and immunoelectron microscopy. We used the antibodies against S-opsin for S-opsin-expressing cones, Rhodopsin for rod photoreceptors, M-opsin for M-opsin-expressing-cones, PKCα for rod ON bipolar cells, calsenilin for type-4 cone OFF bipolar cells, PKRA3b for type-3b cone OFF bipolar cells, and GluA1 and GluK1 for glutamate receptors.
Results :
Necl-1 was expressed throughout the retina, from the ganglion cell layer to the outer nuclear layer. In this study, we focused on Necl-1 at the outer plexiform layer (OPL) where the first synapse-binding site was located. First, Necl-1 was localized around the cell bodies and along the axons of the S-opsin-expressing cones. However, Necl-1 was not co-localized with the rod photoreceptors, although it was localized at the inner segment connected to the outer segment of the M-opsin-expressing cones. Second, Necl-1 was localized around the nuclei of the type-4 cone OFF bipolar cells and at their dendrites connected to the photoreceptors in the OPL. Finally, Necl-1 was localized at the pedicles of the S-opsin-expressing cones. In the Necl-1 (-/-) mice, these dendrites were extended toward the photoreceptor side in the OPL and glutamate receptor was dislocated.
Conclusions :
Necl-1 is localized most likely at the boundary between S-opsin-expressing cones and type-4 cone OFF bipolar cells and regulates the structure of the synapses formed between these cells in the OPL.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.