A MOLECULAR ANALYSIS OF PROTEIN TRAFFICKING IN THE VERTEBRATE RETINA: IMPLICATIONS FOR INTRAFLAGELLAR TRANSPORT AND DISEASE

Vertebrate photoreceptors are highly specialized sensory neurons that utilize a modified cilium known as the outer segment to detect light. Proper trafficking of proteins to the outer segment is essential for photoreceptor function and survival and defects in this process lead to retinal disease. In this dissertation I focus on two aspects of protein trafficking, intracellular vesicular trafficking in photoreceptors and retinal pigmented epithelial (RPE) cells and how it relates to the human disease choroideremia (CHM), and the trafficking of proteins through the photoreceptor cilium. The human retinal degenerative disease choroideremia (CHM) is caused by mutation of the Rab escort protein-1 (REP1) gene, which is required for proper intracellular vesicular trafficking. However, it was unclear whether photoreceptor degeneration in this disease is cell-autonomous, due to defective opsin transport within the photoreceptor, or is noncell-autonomous and a secondary consequence of defective RPE. Utilizing the technique of blastomere transplantation and a zebrafish line with a mutation in the rep1 gene, I show that photoreceptor degeneration in CHM is noncell-autonomous and is caused by defective RPE. The molecular machinery responsible for protein trafficking through the photoreceptor cilium remained unclear for a long time. Recent studies found Intraflagellar Transport (IFT) is the process that mediates cilia formation and transport of proteins through a cilium, and further analyses showed IFT is important for trafficking proteins to the outer segment. However, many details about how IFT works in photoreceptors remained unclear. By analyzing zebrafish harboring a null mutation in the ift57 gene, I show that Ift57 is only required for efficient IFT, and that the Ift57 protein plays a role in the ATP-dependent dissociation of kinesin II from the IFT particle. Lastly, I investigate the role of retrograde IFT in photoreceptors, a process that had yet to be investigated. By utilizing antisense morpholino oligonucleotides to inhibit expression of cytoplasmic dynein-2 (the molecular motor that mediates retrograde IFT) , I show that retrograde IFT is required for outer segment extension and the recycling of IFT proteins.