The Role of TULP1 in Photoreceptor Cells

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TULP1 is a gene we identified to cause autosomal recessive retinitis pigmentosa, a hereditary retinal degeneration blinding nearly 1 million people worldwide. The genetic etiology of RP is known for about 50% of cases; however, the biochemical pathways involved in causing the disease much less. The overall objectives of the proposed studies are to explore the physiologic function of TULP1 in the retina and to define the pathologic mechanism leading to photoreceptor degeneration associated with TULP1 mutations. The TULP family consists of four proteins of unknown function, two of which are linked to photoreceptor degeneration. The two specific aims of this application are designed to test the central hypothesis that TULP1 is a component of the molecular machinery involved in the directional translocation of proteins in photoreceptor cells. The first specific aim is to determine the role of TULP1 in photoreceptor transport pathways. This will be accomplished by using immunocytochemistry to determine whether outer segment proteins, intracellular transport proteins and synaptic proteins are mistargeted in tulpt-/- retinas. Immunoelectron microscopy will be performed to determine if the proteins that are incorrectly transported are cargo on the extracellular vesicles in tulpl-/- retinas. The second specific aim is to determine the function of the TULP1/Dynamin-1 interaction identified in photoreceptor cells. This will be done by identifying the functional domains that interact between TULP1 and Dynamin-1 and determining whether TULP1 mutations that cause RP alter the binding between the two proteins. Experiments are also proposed to generate and phenotype mice lacking Dynamin-1 in photoreceptor cells using Cre-loxP mutagenesis. Transport pathways will be evaluated in these mice as described in aim 1. Since little is known about TULP proteins, discovering information regarding the function of TULP proteins should provide knowledge about the pathways involved in photoreceptor degeneration. It is possible that this work could form the foundation for future studies aimed at evaluating therapeutic modalities that might slow, stop, or reverse the course of retinal degeneration.