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Katie Bales, Mandy J Croyle, Bradley K Yoder, Alecia K Gross; Congenital knock-out of transition zone protein BBS5 reveals cone-rod dystrophy with protein mislocalization. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2053.
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© ARVO (1962-2015); The Authors (2016-present)
The BBSome is a stable network of eight proteins that has been found necessary for normal cilia function and is involved in vesicular trafficking to the ciliary membrane. Mutations occurring in BBSome components result in retinal degeneration-associated ciliopathies. In photoreceptors the precise role of BBSome remains elusive and the function of the protein Bardet-Biedl Syndrome 5 (BBS5) is currently unknown.
BBS5 knock-out (KO) mice were generated with ES cells from Eucomm. Electroretinography (ERG) scotopic and photopic tests were performed on 2 month-, 4 month-, 6 month- and 9 month-old mice using the HMsERG LAB system from OcuScience. For immunohistochemistry (IHC), eyes were enucleated, fixed in 4% paraformaldehyde, embedded and cut into 12 micron sections. Sections were then labeled with antibodies against rhodopsin (B6-30N), transducin (SC-389, Santa Cruz), visual arrestin (SC-67130, Santa Cruz), and stained for wheat germ agglutinin (WGA) and nuclei (DAPI). TUNEL staining was performed to analyze cell death. Transmission electron microscopy (TEM) was performed on 3 month-old animals.
At 2 months of age, mouse ERG responses were completely diminished in BBS5 KO mice, while scotopic responses were reduced. IHC revealed mislocalization of rhodopsin, arrestin and transducin. Labeling with WGA showed that outer segments are shortened significantly by 2 months, while interestingly there is only a reduction of 2 rows of nuclei in the outer nuclear layer by 9 months. TUNEL staining revealed a significant increase of cell death by two months. TEM showed the appearance of mostly normal disks with very few areas of abnormal membranes in BBS5 KO photoreceptors.
Based on these results we find BBS5 plays a role in photoreceptor function and outer segment protein localization. By 2 months of age, BBS5 KO mice lose cone function entirely, accompanied by loss of rod function via ERG analyses. Severe mislocalization of rhodopsin, arrestin and transducin are found as well. TEM reveals the appearance of mostly normal disk formation. These data support the hypothesis that BBS5 plays a vital functional role within photoreceptors and protein trafficking.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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