Molecular mechanisms underlying Retinitis pigmentosa type 2
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The term “Retinitis pigmentosa” (RP) represents a group of inherited, late-onset diseases characterised by progressive retinal degeneration due to photoreceptor death. Mutations in the RP2 gene are found in 7-18% of patients with X-linked RP, one of the most severe forms. The RP2 gene product is a membrane-associated protein which encompasses two distinct domains. The N-terminal domain is well characterised as possessing GTPase-activating protein (GAP) activity towards the small GTPase ARL3 and thus regulate the transport of lipid-modified proteins within the photoreceptor cell. However, it is not known if the loss of this particular function of RP2 is the sole reason that causes the disease, while the role of the protein’s C-terminus remains unknown. This thesis focuses on the characterisation of two novel protein-protein interactions of RP2 with the aim to investigate novel roles of the protein. Firstly, evidence is provided that a highly-conserved cluster of RP2 residues that span both the N- and C-terminus participate in direct interaction with Osteoclast-stimulating factor 1 (OSTF1). Two hypotheses are explored about the potential role of the complex in SRC-mediated RP2 phosphorylation and the regulation of cell motility. Secondly, the catalytic subunit of DNA-dependent protein kinase (DNA PK) is identified as a novel interaction partner of RP2 in cultured cells. The two proteins are shown to co-localise in the nuclear and membrane compartments of a retinal-derived cell line and might engage in a kinase-substrate relationship. So far, no evidence was found that RP2 participates in the canonical function of DNA PK which is the regulation of DNA double-stranded breaks. Finally, the CRISPR/Cas9 genome editing method was applied on zebrafish embryos to generate a novel vertebrate animal model for the loss of RP2 function. One out of three different zebrafish lines with rp2 mutations was shown by histology to have mild late-onset thinning of the photoreceptor outer segments. The present thesis reports previously unexplored aspects of RP2’s function and will, therefore, contribute to understanding the molecular mechanisms that underlie RP. Moreover, this thesis will contribute to the discussion about the usefulness of zebrafish as an RP model.