Form and Function of Photoreceptors in kcnv2 Mutant Zebrafish: Implications for the Human Disease KCNV2 Retinopathy

Abstract

KCNV2 retinopathy is a rare inherited retinal disease caused by mutations in the gene KCNV2, which encodes the potassium channel subunit KV8.2. Expressed by photoreceptors, KV8.2 is a critical component for the efficient generation of a neural response to light. KCNV2 retinopathy is characterized by an abnormal light- and dark-adapted electroretinogram (ERG) waveform, macular photoreceptor degeneration, and variable associated vision deficits such as night blindness, photophobia, a central blind spot, colour blindness, and a reduction in visual acuity. The pathology underlying KCNV2 retinopathy is currently unknown, so I set out to develop a zebrafish animal model of KCNV2 retinopathy with the intention of examining both functional and cell biological changes caused by the absence of KV8.2. Here, I have used CRISPR-Cas9 mutagenesis to generate a line of zebrafish harbouring presumptive loss-of-function variants of kcnv2a and kcnv2b, homologs of human KCNV2. I also developed a novel approach to the zebrafish ERG that allowed us to measure the visual function of kcnv2 mutants. In addition, I evaluated the retinal morphology of kcnv2 mutants with optical coherence tomography (OCT), a common clinical assessment for human ocular diseases. Finally, I performed histology on kcnv2 mutant zebrafish retinal tissue to assess potential cellular changes. kcnv2 mutant zebrafish exhibited subnormal ERG amplitudes and delayed responses in both dark- and light-adapted conditions. Furthermore, the retinae of kcnv2 mutant zebrafish presented with several OCT abnormalities including an unusual signal between the ellipsoid and RPE layers, hyperreflective spots, and retinal holes. Histology revealed dysmorphic photoreceptor outer segments in kcnv2 mutants that were correlated to a reduction in visual function. This thesis documents the development and characterization of a novel zebrafish model of KCNV2 retinopathy. At the juvenile and young adult stages, the zebrafish model already shares phenotypic characteristics with human KCNV2 retinopathy patients, and I anticipate that this model will provide valuable insights into both photoreceptor biology and the enigmatic pathology of KCNV2 retinopathy.