Zebrafish as a Model For Leber Congenital Amaurosis

Abstract

Leber Congenital Amaurosis (LCA) is the most severe form of inherited retinal degeneration, which causes severe visual impairment or blindness before the age of 1 year. Fifteen genes are mutated in LCA patients and mutations in the Retinitis Pigmentosa GTPase Regulator Interacting Protein 1 (RPGRIP1) accounts for ~5% of all the LCA cases. Visual impairment in the patients with homozygous mutations in the RPGRIP1 gene is rapid and progressive, but a late onset cone-rod dystrophy has been reported to be caused by a missense homozygous mutation. The exact function of the RPGRIP1 is not yet fully understood, but it’s found to be localised to the connecting cilium (CC) of the photoreceptors and required for the proper localisation of the ciliary proteins RPGR, NPHP4 and SDCCAG8 in the CC, mutations in which also cause retinal dystrophies. RPGRIP1 is shown to be essential for the rod outer segment elaboration and morphogenesis in mouse model. In this report, an N-ethyl-N-nitrosourea (ENU) induced RPGRIP1 mutant zebrafish has been characterized. I have found that RPGRIP1'1' mutant fish shows progressive photoreceptor degeneration, RPGRIP1 is required for proper morphogenesis of rod outer segment and proper localisation of the RAB8 in the CC of zebrafish photoreceptors. To test the functionality of different photoreceptor cell types, colour preference based behavioural technique has been established. Wild type zebrafish preference for colour has been identified, they prefer blue colour over white and white over red. Using this technique, the functionality of the adult RPGRIP1'1' zebrafish’s cone photoreceptors was evaluated. At 9mpf, the RPGRIP1'1' fish did not swim from red to blue and red to white compartment, but vice versa and in 23mpf RPGRIP1'/' fish unable recognize red and blue colour. The RPGRIP1'1' fish was able to swim between the compartments in UV light illumination confirming the UV cones were functional. From this we have concluded that the red cones got degenerated around 9mpf and blue cones degenerated before 23mpf and UV cones remain functional till 23mpf. In conclusion, RPGRIP1'1' mutant fish is an ideal model to study function of RPGRIP1 in the photoreceptors, LCA and other devastating retinal degeneration disorders. This model would also provide a platform for developing therapeutic treatment for LCA patients.

Date of Award	2015
Original language	English
Awarding Institution	Glasgow Caledonian University
Supervisor	Xinhua Shu (Supervisor), Daphne McCulloch (Supervisor) & John Craft (Supervisor)