C8orf37 knockout mice display abnormal photoreceptor outer segment morphogenesis and progressive photoreceptor degeneration

Abstract

Purpose : The mechanisms underlying protein trafficking and transport from the photoreceptor inner segment (IS) to the base of the outer segment (OS) remains unclear. To address this, we investigated the function of C8ORF37, a novel protein localized at the connecting cilium and IS of photoreceptors.

Methods : We have generated a knockout mouse of C8orf37 using the CRISPR/Cas9 technique. Phenotypical characterizations were conducted by electroretinography (ERG), histology, spectral domain optical coherence tomography (SD-OCT), transmission (TEM) and scanning (SEM) electron microscopy, immunoblotting, and immunostaining. Identification of C8ORF37-interacting proteins was performed by GST-protein pull-down assays and yeast-two hybrid screenings. Confirmation of the identified candidates was performed by coimmunoprecipitation (CoIP) in cell culture.

Results : Both scotopic and photopic ERG responses in C8orf37^-/- mice were reduced by ~50% at various light intensities at 5 weeks of age when compared to C8orf3^+/- mice. SD-OCT analysis of 8-week-old C8orf37^-/- mice showed that the photoreceptor IS/OS junction line was absent compared to age-matched control C8orf3^+/- mice. TEM and SEM examination at P10 revealed that C8orf37^-/- OS were disorganized. Immunoblotting analyses on C8orf37^-/- mice revealed that some OS membrane proteins, as well as their associated non-membrane proteins, were reduced compared to control retinas. Protein-protein interaction screenings identified candidate proteins involved in the dynactin complex and SNARE complex.

Conclusions : Our data suggest that C8ORF37 may function in the OS membrane protein trafficking through interacting with the vesicle-mediated transport machinery.

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