Abstract
Purpose :
Photoreceptors are the main detectors of light that relay visual information to the brain. Establishing proper photoreceptor connectivity during development is critical for proper transmission of visual information. Within the outer retina, photoreceptors synapse selectively to horizontal cells and bipolars. Cone photoreceptors synapse to the dendrites of horizontal cells and cone bipolars, whereas rods connect to the axon terminal of horizontal cells and to the dendrites of rod bipolars. Although the pattern of connections within the retina has been well-described, the molecular mechanisms that guide their selective wiring during development remains unclear.
Methods :
We found a member of the Spectrin family, bII-spectrin to be highly expressed in the developing synaptic layer or OPL where photoreceptors are actively making synaptic connections to their respective partners. Based on the timing and location of expression, we set out to determine if bII-spectrin has a role in photoreceptor connectivity during development. To test our hypothesis, we crossed a floxed allele for bII-spectrin to the Chx10cre transgenic mouse line to conditionally remove bII-spectrin throughout the retina. We refer to this cross as bII-spectrin CKO. Next, we examined bII-spectrin CKO retinas for synaptic defects at various developmental ages.
Results :
Our initial findings reveal disruption of bII-spectrin leads to synaptic defects in the adult retina. Specifically, rod terminals retract into the nuclear layer (i.e. ONL) and processes from horizontal cells and the dendrites of rod bipolars misproject into the ONL. Surprisingly, cone terminals do not retract nor do the dendrites of cone bipolars misproject into the ONL. Consistent with these findings, we find selective loss of pre- and post-synaptic protein expression in the rod synaptic layer but not the cone synaptic layer. Our data suggests that loss of bII-spectrin mainly affects the rod pathway and not the cone pathway. Developmental analysis of bII-spectrin CKO animals reveals that these synaptic phenotypes arise at early stages (i.e. P7-9) when rod synapse formation begins in the outer retina.
Conclusions :
Our work supports a novel role for bII-spectrin in rod photoreceptor connectivity in the developing retina. Future work will focus on deciphering the cellular and molecular mechanisms of how bII-spectrin mediates synapse formation of the rod pathway and not the cone pathway.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.