Retinal Degeneration 3 (RD3) is a small protein necessary for the survival of photoreceptor cells (Friedman, 2006). Mutations that truncate RD3 result in photoreceptor cell degeneration in Leber's Congenital Amaurosis type 12, a severe form of retinal dystrophy that causes severe loss of vision at an early age. Recent evidence suggests that RD3 is required for proper localization of receptor-type guanylate cyclases to rod and cone outer segments (Azadi, 2010). However, RD3's role in vivo in membrane trafficking is not known, nor it is known how mutations in RD3 lead to defects in sensory neuron physiology. In order to study the function of RD3 in vivo, we have identified its homolog in the nematode Caenorhabditis elegans. C. elegans is a strong model to study the normal function of RD3, because it is a powerful genetic model organism with available tools for the in vivo study of the cell biology of genes required for the development and function of sensory neurons. Furthermore, C. elegans sensory neurons that lack RD3 persist, allowing for the study of the effects of the mutation without the confounding effects of cell degeneration. The nematode homolog of RD3 is enriched in a subset of ciliated sensory neurons, including the chemosensory BAG neurons. In order to better understand the functions of RD3 in vivo, we used the CRISPR Cas-9 method (Friedland, 2013) to generate loss-of-function alleles. Using these mutant alleles, we have found that the C. elegans homologue of RD3 is required for the proper function of the BAG neurons. BAG neurons share characteristics with retinal photoreceptor neurons, including components of the signaling transduction apparatus, which consists of a receptor type guanylate cyclase, and the cyclic nucleotide gated (CNG) channels TAX-2/TAX-4 (Hallem, 2011). By using live cell and functional imaging techniques, behavioral studies, we will determine the in vivo function of RD3 in a ciliated sensory neuron.
Mutations in the Retinal Degeneration 3 (RD3) gene lead to a severe early onset retinal degeneration. The normal function for RD3 and many of the retinal degeneration genes remains unknown, partly because genetic study of mutations in these genes is complicated by the early death of photoreceptors in mammals. Determining the molecular mechanisms that require RD3 in ciliated sensory neurons in vivo will be instrumental in learning about specialized cellular processes that are essential for sensory neuron function, and provide knowledge that can be adapted to develop much needed diagnostics and therapeutics for hereditary retinopathies.
| Martínez-Velázquez, Luis A; Ringstad, Niels (2018) Antagonistic regulation of trafficking to Caenorhabditis elegans sensory cilia by a Retinal Degeneration 3 homolog and retromer. Proc Natl Acad Sci U S A 115:E438-E447 |
