Abstract
The photoreceptor outer segment is the canonical example of a modified and highly specialized cilium, with an expanded membrane surface area in the form of disks or lamellae for efficient light detection. Many ciliary proteins are essential for normal photoreceptor function and cilium dysfunction often results in retinal degeneration leading to impaired vision. Herein, we investigate the function and localization of the ciliary G-protein RAB28 in zebrafish cone photoreceptors. CRISPR-Cas9 generated rab28 mutant zebrafish display significantly reduced shed outer segment material/phagosomes in the RPE at 1 month post fertilization (mpf), but otherwise normal visual function up to 21 dpf and retinal structure up to 12 mpf. Cone photoreceptor-specific transgenic reporter lines show Rab28 localizes almost exclusively to outer segments, independently of GTP/GDP nucleotide binding. Co-immunoprecipitation analysis demonstrates tagged Rab28 interacts with components of the phototransduction cascade, including opsins, phosphodiesterase 6C and guanylate cyclase 2D. Our data shed light on RAB28 function in cones and provide a model for RAB28-associated cone-rod dystrophy.
Highlights
The photoreceptor outer segment (OS) is an elaborate membranous organelle which functions in the detection of light stimuli and their conversion to electrical signals via phototransduction (Fain et al, 2010; Goldberg et al, 2016)
A product was successfully amplified in three reactions, the others failing either because the prediction of exon placement was incorrect or the introns were too large to amplify by PCR (Figure 1B)
Loss of rab28 Leads to Reduced Cone OS Shedding in Zebrafish
Summary
The photoreceptor outer segment (OS) is an elaborate membranous organelle which functions in the detection of light stimuli and their conversion to electrical signals via phototransduction (Fain et al, 2010; Goldberg et al, 2016). Rab Function in Zebrafish Cone Photoreceptors polymerization (Spencer et al, 2019) and gradually migrate upwards as the oldest disks/lamellae at the OS tip are shed and phagocytosed daily by the retinal pigment epithelium (RPE). RAB28 null and hypomorphic alleles cause autosomal recessive cone-rod dystrophy (arCRD) (Roosing et al, 2013; Riveiro-Álvarez et al, 2015; Lee et al, 2017). To our knowledge, this is the only example of inherited PRD arising exclusively from a disorder of cone OS (COS) shedding
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