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A. M. Jensen, Y.-C. Hsu; Multiple Domains in the Crumbs Homolog 2a (Crb2a) Protein Are Required for Its Localization and Function in Rod Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2715.
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Vertebrate retinal photoreceptors are morphologically complex cells that have two large apical regions, the inner segment and the outer segment. The outer segment is continuously renewed throughout the life of the animal. The molecular and cellular mechanisms that underlie vertebrate photoreceptor morphogenesis and the maintenance of the outer segment remain unknown. The Crumbs (Crb) complex is a key regulator of apical membrane identity and size in epithelia and Drosophila photoreceptors. Mutations in the human gene CRUMBS HOMOLOG 1 (CRB1) are associated with early and severe vision loss. Our study sought to understand what domains in Crb proteins are important for its localization and function in photoreceptors
In order to begin to understand the role of the Crb family of proteins in vertebrate photoreceptors we generated transgenic zebrafish in which rod photoreceptors overexpress full-length Crb2a protein and Crb2a constructs that lack specific domains.
We examined the localization of these Crb2a constructs and their effects on rod morphology using confocal microscopy. Only full-length Crb2a (Crb2aFL) approximated the normal localization of Crb2a protein and localized to the inner segment. Many constructs showed outer segment localization, suggesting that the outer segment maybe the default destination for transmembrane proteins lacking intracellular or extracellular anchoring. Overexpression of several constructs led to a modest increase in outer segment size. Interestingly, overexpression of Crb2aFL greatly increased inner segment size, and massively increased the number of ribosomes, suggesting that Crb2a may regulate the Tor pathway.
All domains in Crb2a are important for its function and Crb proteins in photoreceptors may regulate the Tor pathway.
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