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Brian D. Perkins, Lynn Dudinsky; Rapid Photoreceptor Degeneration Occurs In Zebrafish arl13b Mutants Following Suppression Of Pcp Signaling. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6554.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in ARL13b are linked to Joubert Syndrome, a ciliopathy characterized by a distinctive midbrain-hindbrain malformation, kidney cysts, and varying degrees of retinal degeneration. Patients with mutations in ARL13b reported vision problems but ERG recordings were normal. Arl13b localizes to cilia but its function(s) are poorly understood. As genetic interactions between mutant alleles of cilia loci can modulate pathological expression, it is possible that mutant ARL13b alleles contribute to other diseases. Mice and zebrafish with Arl13b mutations exhibit cilia defects but the retinal phenotype has not been explored. As morpholino suppression of arl13b leads to phenotypes in zebrafish consistent with defects in planar cell polarity (PCP), we hypothesize that Arl13b and PCP components function together to enhance the arl13b phenotypic spectrum within photoreceptors.
Photoreceptor structure in arl13b mutants was examined in transverse sections and in cross-section by electron microscopy. Immunohistochemistry was performed to examine rhodopsin localization and the localization of various cilia proteins. Morpholinos against vangl2 or bbs8 were co-injected with arl13b morpholinos into 1-cell embryos. Genetic mosaic animals were generated by blastula transplantation using arl13b:Tg(TαC:GFP) transgenic as donors.
Zebrafish arl13b mutant photoreceptors did not exhibit overt signs of retinal degeneration by electron microscopy or immunohistochemistry at 5 days post fertilization (dpf). Starting at 14 dpf and continuing through 30 dpf, cells lacking Arl13b died following transplantation into wild-type host animals, whereas control transplanted cells survived. Mild suppression of arl13b with vangl2 or bbs8 by co-injection of morpholino oligonucleotides resulted in shorter photoreceptor outer segments and significant opsin mislocalization. None of these phenotypes are present in animals injected with single morpholinos.
Loss of arl13b does not cause early photoreceptor degeneration but did lead to slow photoreceptor degeneration following cell transplantation. Furthermore, arl13b genetically interacts with components of the PCP pathway and multiple BBS genes. These results suggest that retinal pathology does occur in Joubert patients and the rate of degeneration in Joubert Syndrome may be influenced by additional genetic factors.
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