Morphometric analysis of photoreceptors in the zebrafish pde6c mutant with and without exposure to Schisandrin B

Abstract

Purpose : Schisandrin B (SchB) is a naturally-derived compound that enhances the light sensation of a zebrafish pde6c mutant. This mutant carries a mutation in the pde6c gene (phosphodiesterase 6C, cGMP-specific, cone, alpha prime) which causes cone degeneration. Consequently, the bystander rods degenerate too. These degenerating photoreceptors can be the target of SchB treatment, as its enhancing effect on light sensation was substantially attenuated by eye enucleation of the treated larvae. To investigate SchB’s effect on pde6c photoreceptors, we conducted morphometric analysis of these cells in the pde6c mutant with and without SchB treatment.

Methods : The pde6c embryos were exposed to an optimized concentration of SchB or the drug carrier DMSO as controls. These embryos were treated from 3 days postfertilization (dpf) to 6 dpf. Then, their retinas were microdissected for photoreceptor immunostaining. After the immunostaining procedure, the stained retinas were imaging by confocal microscopy. The resulting z-stack confocal images of the retinas were analyzed to extract several parameters of the PRs in three dimensions for statistical analysis.

Results : Without the SchB treatment, the pde6c rods generally appeared more prominent than the wild-type (WT) ones, a phenomenon that had been previously described. This was also supported by a larger cell volume measured in this study (p-values = 0.0013). Under the SchB treatment, the pde6c rods became significantly smaller compared with the untreated ones (p-value = 0.0008). The other morphological parameters and cell counts were not significantly different between the pde6c rods with and without SchB treatment. For cones, they were obviously more prominent and less in number in the pde6c mutants without the SchB treatment compared with those in the WT controls. Unlike rods, cone morphology or count in the pde6c mutants was not substantially altered by the SchB treatment.

Conclusions : Together, these results suggest that the SchB treatment likely acted on the degenerating pde6c rods and reduced their abnormally-large volume to the WT level. These rods might have transduced light signal better, and in turn enhanced the light sensation of the pde6c mutants.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.