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Vol. 14, Issue 8, 3400-3413, August 2003

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The Role of Subunit Assembly in Peripherin-2 Targeting to Rod Photoreceptor Disk Membranes and Retinitis Pigmentosa

Christopher J.R. Loewen ^*, Orson L. Moritz , Beatrice M. Tam , David S. Papermaster , and Robert S. Molday ^*  

^* Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3; Department of Ophthalmology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3; and Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06032-3705

Submitted February 10, 2003; Revised March 19, 2003; Accepted April 9, 2003
Monitoring Editor: Benjamin Glick

Peripherin-2 is a member of the tetraspanin family of membrane proteins that plays a critical role in photoreceptor outer segment disk morphogenesis. Mutations in peripherin-2 are responsible for various retinal degenerative diseases including autosomal dominant retinitis pigmentosa (ADRP). To identify determinants required for peripherin-2 targeting to disk membranes and elucidate mechanisms underlying ADRP, we have generated transgenic Xenopus tadpoles expressing wild-type and ADRP-linked peripherin-2 mutants as green fluorescent fusion proteins in rod photoreceptors. Wild-type peripherin-2 and P216L and C150S mutants, which assemble as tetramers, targeted to disk membranes as visualized by confocal and electron microscopy. In contrast the C214S and L185P mutants, which form homodimers, but not tetramers, were retained in the rod inner segment. Only the P216L disease mutant induced photoreceptor degeneration. These results indicate that tetramerization is required for peripherin-2 targeting and incorporation into disk membranes. Tetramerization-defective mutants cause ADRP through a deficiency in wild-type peripherin-2, whereas tetramerization-competent P216L peripherin-2 causes ADRP through a dominant negative effect, possibly arising from the introduction of a new oligosaccharide chain that destabilizes disks. Our results further indicate that a checkpoint between the photoreceptor inner and outer segments allows only correctly assembled peripherin-2 tetramers to be incorporated into nascent disk membranes.

Abbreviations used: GFP, green fluorescent protein; ROS, rod outer segments; ADRP, autosomal dominant retinitis pigmentosa; WT, wild-type; DTT, dithiothreitol.

Corresponding author. E-mail address: molday{at}interchange.ubc.ca.

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