Differential synaptic distribution of the scaffold proteins Cask and Caskin1 in the bovine retina.

Scaffold proteins organize pre- and postsynaptic compartments and align pre- and postsynaptic events. Cask is a multi-domain scaffold protein essential for brain synaptic functions. Caskin1 is a recently discovered, brain-specific Cask-interacting multi-domain protein of unknown function. In the present study, we determined the localization of these scaffold proteins in the bovine retina. The retina contains tonically active ribbon synapses and conventional synapses. We found Cask highly enriched in virtually all retinal synapses. Cask was localized in close vicinity to the active zone protein RIM1/2 in ribbon and conventional synapses. Caskin1 is also enriched in retinal synapses but is present only in a subset of Cask-positive synapses. These findings suggest that Cask plays an important role in all retinal synapses. In contrast, Caskin1 appears to execute more specialized functions in distinct sets of retinal synapses, possibly for neuronal pathway formation and stabilization of distinct synaptic contacts.