The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform

Muna I Naash - One of the best experts on this subject based on the ideXlab platform.

  • Photoreceptor disc enclosure is tightly controlled by Peripherin-2 oligomerization.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 2021
    Co-Authors: Tylor R Lewis, Muna I Naash, Muayyad R. Al-ubaidi, Mustafa S Makia, Carson M Castillo, Vadim Y Arshavsky
    Abstract:

    Mutations in the PRPH2 gene encoding the photoreceptor-specific protein PRPH2 (also known as Peripherin-2 or rds) cause a broad range of autosomal dominant retinal diseases. Most of these mutations affect the structure of the light-sensitive photoreceptor outer segment, which is composed of a stack of flattened "disc" membranes surrounded by the plasma membrane. The outer segment is renewed on a daily basis in a process whereby new discs are added at the outer segment base and old discs are shed at the outer segment tip. New discs are formed as serial membrane evaginations, which eventually enclose through a complex process of membrane remodeling (completely in rods and partially in cones). As disc enclosure proceeds, PRPH2 localizes to the rims of enclosed discs where it forms oligomers which fortify the highly curved membrane structure of these rims. In this study, we analyzed the outer segment phenotypes of mice of both sexes bearing a single copy of either the C150S or the Y141C PRPH2 mutation known to prevent or increase the degree of PRPH2 oligomerization, respectively. Strikingly, both mutations increased the number of newly forming, not-yet-enclosed discs, indicating that the precision of disc enclosure is regulated by PRPH2 oligomerization. Without tightly controlled enclosure, discs occasionally over-elongate and form large membranous "whorls" instead of disc stacks. These data show that the defects in outer segment structure arising from abnormal PRPH2 oligomerization are manifested at the stage of disc enclosure.SIGNIFICANCE STATEMENT:The light-sensitive photoreceptor outer segment contains a stack of flattened "disc" membranes that are surrounded, or "enclosed", by the outer segment membrane. Disc enclosure is an adaptation increasing photoreceptor light sensitivity by facilitating the diffusion of the second messenger along the outer segment axes. However, the molecular mechanisms by which photoreceptor discs enclose within the outer segment membrane remain poorly understood. We now demonstrate that oligomers of the photoreceptor-specific protein Peripherin-2, or PRPH2, play an active role in this process. We further propose that defects in disc enclosure due to abnormal PHPH2 oligomerization result in major structural abnormalities of the outer segment, ultimately leading to loss of visual function and cell degeneration in PRPH2 mutant models and human patients.

  • Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration.
    International journal of molecular sciences, 2020
    Co-Authors: Ayse M Genc, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Sinha, Muna I Naash
    Abstract:

    The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component Peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)P23H/+ and Prph2Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in RhoP23H/+/Rtbdn-/- and Prph2Y141C/+/Rtbdn-/- retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

  • Syntaxin 3 is essential for photoreceptor outer segment protein trafficking and survival.
    Proceedings of the National Academy of Sciences of the United States of America, 2020
    Co-Authors: Mashal Kakakhel, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Lars Tebbe, David M. Sherry, Muna I Naash
    Abstract:

    Trafficking of photoreceptor membrane proteins from their site of synthesis in the inner segment (IS) to the outer segment (OS) is critical for photoreceptor function and vision. Here we evaluate the role of syntaxin 3 (STX3), in trafficking of OS membrane proteins such as Peripherin 2 (PRPH2) and rhodopsin. Photoreceptor-specific Stx3 knockouts [Stx3f/f(iCre75) and Stx3f/f(CRX-Cre)] exhibited rapid, early-onset photoreceptor degeneration and functional decline characterized by structural defects in IS, OS, and synaptic terminals. Critically, in the absence of STX3, OS proteins such as PRPH2, the PRPH2 binding partner, rod outer segment membrane protein 1 (ROM1), and rhodopsin were mislocalized along the microtubules to the IS, cell body, and synaptic region. We find that the PRPH2 C-terminal domain interacts with STX3 as well as other photoreceptor SNAREs, and our findings indicate that STX3 is an essential part of the trafficking pathway for both disc (rhodopsin) and rim (PRPH2/ROM1) components of the OS.

  • ROM1 contributes to phenotypic heterogeneity in PRPH2-associated retinal disease.
    Human molecular genetics, 2020
    Co-Authors: Daniel G. Strayve, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Mashal Kakakhel, Haarthi Sakthivel, Muna I Naash
    Abstract:

    Peripherin 2 (PRPH2) is a retina-specific tetraspanin protein essential for the formation of rod and cone photoreceptor outer segments (OS). Patients with mutations in PRPH2 exhibit severe retinal degeneration characterized by vast inter- and intra-familial phenotypic heterogeneity. To help understand contributors to this within-mutation disease variability, we asked whether the PRPH2 binding partner rod OS membrane protein 1 (ROM1) could serve as a phenotypic modifier. We utilized knockin and transgenic mouse models to evaluate the structural, functional and biochemical effects of eliminating one allele of Rom1 (Rom1+/-) in three different Prph2 models which mimic human disease: C213Y Prph2 (Prph2C/+), K153Del Prph2 (Prph2K/+) and R172W (Prph2R172W). Reducing Rom1 in the absence of Prph2 mutations (Rom1+/-) had no effect on retinal structure or function. However, the effects of reducing Rom1 in the presence of Prph2 mutations were highly variable. Prph2K/+/Rom1+/- mice had improved rod and cone function compared with Prph2K/+ as well as amelioration of K153Del-associated defects in PRPH2/ROM1 oligomerization. In contrast, Prph2R172W/Rom1+/- animals had worsened rod and cone function and exacerbated retinal degeneration compared with Prph2R172W animals. Removing one allele of Rom1 had no effect in Prph2C/+. Combined, our findings support a role for non-pathogenic ROM1 null variants in contributing to phenotypic variability in mutant PRPH2-associated retinal degeneration. Since the effects of Rom1 reduction are variable, our data suggest that this contribution is specific to the type of Prph2 mutation.

  • Photoreceptor Disc Enclosure Occurs in the Absence of Normal Peripherin-2/rds Oligomerization.
    Frontiers in cellular neuroscience, 2020
    Co-Authors: Tylor R Lewis, Muayyad R. Al-ubaidi, Mustafa S Makia, Mashal Kakakhel, Vadim Y Arshavsky, Muna I Naash
    Abstract:

    Mutations in the Peripherin-2 gene (PRPH2, also known as rds) cause a heterogeneous range of autosomal dominant retinal diseases. PRPH2 encodes a photoreceptor-specific tetraspanin protein, PRPH2, that is a main structural component of the photoreceptor outer segment. PRPH2 distributes to the rims of outer segment disc membranes as they undergo the process of disc membrane enclosure. Within these rims, PRPH2 exists in homo-oligomeric form or as a hetero-oligomer with another tetraspanin protein, ROM1. While complete loss of PRPH2 prevents photoreceptor outer segment formation, mutations affecting the state of its oligomerization, including C150S, C213Y and Y141C, produce outer segment structural defects. In this study, we addressed whether any of these mutations also affect disc enclosure. We employed recently developed methodology for ultrastructural analysis of the retina, involving tissue processing with tannic acid, to assess the status of disc enclosure in knockin mouse models bearing either one or two alleles of the C150S, C213Y and Y141C PRPH2 mutations. While varying degrees of outer segment structural abnormalities were observed in each of these mouse models, they contained both newly forming "open" discs and mature "enclosed" discs. These data demonstrate that normal PRPH2 oligomerization is not essential for photoreceptor disc enclosure.

Shannon M Conley - One of the best experts on this subject based on the ideXlab platform.

  • Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration.
    International journal of molecular sciences, 2020
    Co-Authors: Ayse M Genc, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Sinha, Muna I Naash
    Abstract:

    The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component Peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)P23H/+ and Prph2Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in RhoP23H/+/Rtbdn-/- and Prph2Y141C/+/Rtbdn-/- retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

  • Syntaxin 3 is essential for photoreceptor outer segment protein trafficking and survival.
    Proceedings of the National Academy of Sciences of the United States of America, 2020
    Co-Authors: Mashal Kakakhel, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Lars Tebbe, David M. Sherry, Muna I Naash
    Abstract:

    Trafficking of photoreceptor membrane proteins from their site of synthesis in the inner segment (IS) to the outer segment (OS) is critical for photoreceptor function and vision. Here we evaluate the role of syntaxin 3 (STX3), in trafficking of OS membrane proteins such as Peripherin 2 (PRPH2) and rhodopsin. Photoreceptor-specific Stx3 knockouts [Stx3f/f(iCre75) and Stx3f/f(CRX-Cre)] exhibited rapid, early-onset photoreceptor degeneration and functional decline characterized by structural defects in IS, OS, and synaptic terminals. Critically, in the absence of STX3, OS proteins such as PRPH2, the PRPH2 binding partner, rod outer segment membrane protein 1 (ROM1), and rhodopsin were mislocalized along the microtubules to the IS, cell body, and synaptic region. We find that the PRPH2 C-terminal domain interacts with STX3 as well as other photoreceptor SNAREs, and our findings indicate that STX3 is an essential part of the trafficking pathway for both disc (rhodopsin) and rim (PRPH2/ROM1) components of the OS.

  • ROM1 contributes to phenotypic heterogeneity in PRPH2-associated retinal disease.
    Human molecular genetics, 2020
    Co-Authors: Daniel G. Strayve, Shannon M Conley, Muayyad R. Al-ubaidi, Mustafa S Makia, Mashal Kakakhel, Haarthi Sakthivel, Muna I Naash
    Abstract:

    Peripherin 2 (PRPH2) is a retina-specific tetraspanin protein essential for the formation of rod and cone photoreceptor outer segments (OS). Patients with mutations in PRPH2 exhibit severe retinal degeneration characterized by vast inter- and intra-familial phenotypic heterogeneity. To help understand contributors to this within-mutation disease variability, we asked whether the PRPH2 binding partner rod OS membrane protein 1 (ROM1) could serve as a phenotypic modifier. We utilized knockin and transgenic mouse models to evaluate the structural, functional and biochemical effects of eliminating one allele of Rom1 (Rom1+/-) in three different Prph2 models which mimic human disease: C213Y Prph2 (Prph2C/+), K153Del Prph2 (Prph2K/+) and R172W (Prph2R172W). Reducing Rom1 in the absence of Prph2 mutations (Rom1+/-) had no effect on retinal structure or function. However, the effects of reducing Rom1 in the presence of Prph2 mutations were highly variable. Prph2K/+/Rom1+/- mice had improved rod and cone function compared with Prph2K/+ as well as amelioration of K153Del-associated defects in PRPH2/ROM1 oligomerization. In contrast, Prph2R172W/Rom1+/- animals had worsened rod and cone function and exacerbated retinal degeneration compared with Prph2R172W animals. Removing one allele of Rom1 had no effect in Prph2C/+. Combined, our findings support a role for non-pathogenic ROM1 null variants in contributing to phenotypic variability in mutant PRPH2-associated retinal degeneration. Since the effects of Rom1 reduction are variable, our data suggest that this contribution is specific to the type of Prph2 mutation.

  • The Role of the Prph2 C-Terminus in Outer Segment Morphogenesis.
    Retinal Degenerative Diseases, 2019
    Co-Authors: Shannon M Conley, Muayyad R. Al-ubaidi, Muna I Naash
    Abstract:

    Peripherin 2 (also known as RDS/Prph2) is localized to the rims of rod and cone outer segment (OS) discs. The C-terminus of Prph2 is a critical functional domain, but its exact role is still unknown. In this mini review, we describe work on the Prph2 C-terminus, highlighting its role as a regulator of protein trafficking, membrane curvature, ectosome secretion, and membrane fusion. Evidence supports a role for the Prph2 C-terminus in these processes and demonstrates that it is necessary for the initiation of OS morphogenesis.

  • Novel molecular mechanisms for Prph2-associated pattern dystrophy.
    FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 2019
    Co-Authors: Dibyendu Chakraborty, Shannon M Conley, Muayyad R. Al-ubaidi, Daniel G. Strayve, Mustafa S Makia, Mashal Kakahel, Muna I Naash
    Abstract:

    Mutations in Peripherin 2 (PRPH2) have been associated with retinitis pigmentosa (RP) and macular/pattern dystrophies, but the origin of this phenotypic variability is unclear. The majority of Prph2 mutations are located in the large intradiscal loop (D2), a region that contains seven cysteines involved in intra- and intermolecular disulfide bonding and protein folding. A mutation at cysteine 213, which is engaged in an intramolecular disulfide bond, leads to butterfly-shaped pattern dystrophy in humans, in sharp contrast to mutations in the adjacent cysteine at position 214 which result in RP. To help understand this unexpected phenotypic variability, we generated a knockin mouse line carrying the C213Y disease mutation. The mutant Prph2 protein lost the ability to oligomerize with rod outer segment membrane protein 1 (Rom1), but retained the ability to form homotetramers. C213Y heterozygotes had significantly decreased overall Prph2 levels as well as decreased rod and cone function. Critically, supplementation with extra wild-type Prph2 protein elicited improvements in Prph2 protein levels and rod outer segment structure, but not functional rescue in rods or cones. These findings suggest that not all interruptions of D2 loop intramolecular disulfide bonding lead to haploinsufficiency-related RP, but rather that more subtle changes can lead to mutant proteins stable enough to exert gain-of-function defects in rods and cones. This outcome highlights the difficulty in targeting Prph2-associated gain-of-function disease and suggests that elimination of the mutant protein will be a pre-requisite for any curative therapeutic strategy.

Robert S. Molday - One of the best experts on this subject based on the ideXlab platform.

  • Peripherin diverts ciliary ectosome release to photoreceptor disc morphogenesis
    The Journal of cell biology, 2017
    Co-Authors: Robert S. Molday, Andrew F. X. Goldberg
    Abstract:

    Formation of membrane discs in photoreceptor cells requires evagination of its ciliary plasma membrane by an unknown molecular mechanism. Salinas et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201608081) show that Peripherin (also known as Peripherin-2 or Peripherin-2/rds) diverts membrane traffic to photoreceptor disc formation by inhibiting ectosome release from the cilium.

  • Interaction of 4.1G and cGMP-gated channels in rod photoreceptor outer segments.
    Journal of cell science, 2013
    Co-Authors: Christiana L Cheng, Robert S. Molday
    Abstract:

    In photoreceptors, the assembly of signaling molecules into macromolecular complexes is important for phototransduction and maintaining the structural integrity of rod outer segments (ROSs). However, the molecular composition and formation of these complexes are poorly understood. Using immunoprecipitation and mass spectrometry, 4.1G was identified as a new interacting partner for the cyclic-nucleotide gated (CNG) channels in ROSs. 4.1G is a widely expressed multifunctional protein that plays a role in the assembly and stability of membrane protein complexes. Multiple splice variants of 4.1G were cloned from bovine retina. A smaller splice variant of 4.1G selectively interacted with CNG channels not associated with Peripherin-2-CNG channel complex. A combination of truncation studies and domain-binding assays demonstrated that CNG channels selectively interacted with 4.1G through their FERM and CTD domains. Using immunofluorescence, labeling of 4.1G was seen to be punctate and partially colocalized with CNG channels in the ROS. Our studies indicate that 4.1G interacts with a subset of CNG channels in the ROS and implicate this protein-protein interaction in organizing the spatial arrangement of CNG channels in the plasma membrane of outer segments.

  • Retinal Dystrophies: Functional Genomics to Gene Therapy: Novartis Foundation Symposium 255 - Role of Subunit Assembly in Autosomal Dominant Retinitis Pigmentosa Linked to Mutations in Peripherin 2
    Novartis Foundation symposium, 2008
    Co-Authors: Robert S. Molday, Laurie L. Molday, Christopher J. R. Loewen
    Abstract:

    Peripherin 2 is a photoreceptor-specific membrane protein implicated in outer segment disk morphogenesis and linked to various retinopathies including autosomal dominant retinitis pigmentosa (ADRP). Peripherin 2 and ROM1 assemble as a mixture of core noncovalent homomeric and heteromeric tetramers that further link together through disulfide bonds to form higher order oligomers. These complexes are critical for disk rim formation and outer segment structure through interaction with the cGMP-gated channel and other photoreceptor proteins. We have examined the role of subunit assembly in Peripherin 2 targeting to disks, outer segment structure, and photoreceptor degeneration by examining molecular and cellular properties of Peripherin 2 mutants in COS-1 cells and transgenic Xenopus laevis rod photoreceptors. Wild-type (WT) and the ADRP-linked P216L mutant were transported and incorporated into newly formed outer segment disks of transgenic X. laevis. The P216L mutant, however, induced progressive outer segment instability and photoreceptor degeneration possibly through the introduction of a new N-linked oligosaccharide chain. In contrast, the C214S and L185P disease-linked, tetramerization-defective mutants, were retained in the inner segment, but did not affect outer segment structure or induce photoreceptor degeneration. Together, these results indicate that Peripherin 2 mutations can cause ADRP either through a deficiency in WT Peripherin 2 (C214S, 1.185P) or by a dominant negative effect on disk stability (P216L).

  • role of subunit assembly in autosomal dominant retinitis pigmentosa linked to mutations in Peripherin 2
    Novartis Foundation symposium, 2004
    Co-Authors: Robert S. Molday, Laurie L. Molday, Christopher J. R. Loewen
    Abstract:

    Peripherin 2 is a photoreceptor-specific membrane protein implicated in outer segment disk morphogenesis and linked to various retinopathies including autosomal dominant retinitis pigmentosa (ADRP). Peripherin 2 and ROM1 assemble as a mixture of core noncovalent homomeric and heteromeric tetramers that further link together through disulfide bonds to form higher order oligomers. These complexes are critical for disk rim formation and outer segment structure through interaction with the cGMP-gated channel and other photoreceptor proteins. We have examined the role of subunit assembly in Peripherin 2 targeting to disks, outer segment structure, and photoreceptor degeneration by examining molecular and cellular properties of Peripherin 2 mutants in COS-1 cells and transgenic Xenopus laevis rod photoreceptors. Wild-type (WT) and the ADRP-linked P216L mutant were transported and incorporated into newly formed outer segment disks of transgenic X. laevis. The P216L mutant, however, induced progressive outer segment instability and photoreceptor degeneration possibly through the introduction of a new N-linked oligosaccharide chain. In contrast, the C214S and L185P disease-linked, tetramerization-defective mutants, were retained in the inner segment, but did not affect outer segment structure or induce photoreceptor degeneration. Together, these results indicate that Peripherin 2 mutations can cause ADRP either through a deficiency in WT Peripherin 2 (C214S, 1.185P) or by a dominant negative effect on disk stability (P216L).

  • The Role of Subunit Assembly in Peripherin-2 Targeting to Rod Photoreceptor Disk Membranes and Retinitis Pigmentosa
    Molecular biology of the cell, 2003
    Co-Authors: Christopher J. R. Loewen, Orson L Moritz, Beatrice M. Tam, David S. Papermaster, Robert S. Molday
    Abstract:

    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.

Michael W. Stuck - One of the best experts on this subject based on the ideXlab platform.

  • Prph2 initiates outer segment morphogenesis but maturation requires Prph2/Rom1 oligomerization.
    Human molecular genetics, 2019
    Co-Authors: Shannon M Conley, Rahel Zulliger, Michael W. Stuck, Jamie N. Watson, Justin L. Burnett, Muna I Naash
    Abstract:

    The retinal disease gene Peripherin 2 (PRPH2) is essential for the formation of photoreceptor outer segments (OSs), where it functions in oligomers with and without its homologue ROM1. However, the precise role of these proteins in OS morphogenesis is not understood. By utilizing a knock-in mouse expressing a chimeric protein comprised of the body of Rom1 and the C-terminus of Prph2 (termed RRCT), we find that the Prph2 C-terminus is necessary and sufficient for the initiation of OSs, while OS maturation requires the body of Prph2 and associated large oligomers. Importantly, dominant-negative physiological and biochemical defects in RRCT heterozygous rods are rescued by removing Rom1, suggesting Rom1 is a regulator for OS formation. Our experiments evaluating Prph2 trafficking show that Rom1 is a key determinant of whether Prph2 complexes utilize conventional versus unconventional (Golgi bypass) secretory pathways to reach the OS. These findings significantly advance our understanding of the molecular underpinnings of OS morphogenesis and particularly the role of Rom1.

  • Rom1 converts Y141C-Prph2-associated pattern dystrophy to retinitis pigmentosa
    Human molecular genetics, 2017
    Co-Authors: Shannon M Conley, Michael W. Stuck, Jamie N. Watson, Muna I Naash
    Abstract:

    Mutations in Peripherin 2 (PRPH2), also known as retinal degeneration slow/RDS, lead to various retinal degenerations including retinitis pigmentosa (RP) and macular/pattern dystrophy (MD/PD). PRPH2-associated disease is often characterized by a phenotypic variability even within families carrying the same mutation, raising interest in potential modifiers. PRPH2 oligomerizes with its homologue rod outer segment (OS) membrane protein 1 (ROM1), and non-pathogenic PRPH2/ROM1 mutations, when present together, lead to digenic RP. We asked whether ROM1 could modify the phenotype of a PRPH2 mutation associated with a high degree of intrafamilial phenotypic heterogeneity: Y141C. In vitro, Y141C-Prph2 showed signs of retention in the endoplasmic reticulum (ER), however co-expression with Rom1 rescued this phenotype. In the heterozygous Y141C knockin mouse model (Prph2Y/+), Y141C-Prph2 and Rom1 formed abnormal complexes but were present at normal levels. Abnormal complexes were eliminated in the absence of Rom1 (Prph2Y/+/Rom1-/-) and total Prph2 levels were reduced to those found in the haploinsufficient Prph2+/- RP model. The biochemical changes had functional and structural consequences; while Prph2Y/+ animals exhibited a cone-rod electroretinogram defect, Prph2Y/+/Rom1-/- animals displayed a rod-dominant phenotype and OSs similar to those seen in the Prph2+/-. These data show that ablation of Rom1 results in the conversion of an MD/PD phenotype characterized by cone functional defects and the formation of abnormal Prph2/Rom1 complexes to an RP phenotype characterized by rod-dominant functional defects and reductions in total Prph2 protein. Thus one method by which ROM1 may act as a disease modifier is by contributing to the large variability in PRPH2-associated disease phenotypes.

  • PRPH2/RDS and ROM-1: Historical context, current views and future considerations.
    Progress in retinal and eye research, 2016
    Co-Authors: Michael W. Stuck, Shannon M Conley, Muna I Naash
    Abstract:

    Peripherin 2 (PRPH2), also known as RDS (retinal degeneration slow) is a photoreceptor specific glycoprotein which is essential for normal photoreceptor health and vision. PRPH2/RDS is necessary for the proper formation of both rod and cone photoreceptor outer segments, the organelle specialized for visual transduction. When PRPH2/RDS is defective or absent, outer segments become disorganized or fail to form entirely and the photoreceptors subsequently degenerate. Multiple PRPH2/RDS disease-causing mutations have been found in humans, and they are associated with various blinding diseases of the retina such as macular degeneration and retinitis pigmentosa, the vast majority of which are inherited dominantly, though recessive LCA and digenic RP have also been associated with RDS mutations. Since its initial discovery, the scientific community has dedicated a considerable amount of effort to understanding the molecular function and disease mechanisms of PRPH2/RDS. This work has led to an understanding of how the PRPH2/RDS molecule assembles into complexes and functions as a necessary part of the machinery that forms new outer segment discs, as well as leading to fundamental discoveries about the mechanisms that underlie OS biogenesis. Here we discuss PRPH2/RDS-associated research and how experimental results have driven the understanding of the PRPH2/RDS protein and its role in human disease.

  • SNAREs Interact with Retinal Degeneration Slow and Rod Outer Segment Membrane Protein-1 during Conventional and Unconventional Outer Segment Targeting.
    PloS one, 2015
    Co-Authors: Rahel Zulliger, Shannon M Conley, Maggie L Mwoyosvi, Michael W. Stuck, Seifollah Azadi, Muna I Naash
    Abstract:

    Mutations in the photoreceptor protein Peripherin-2 (also known as RDS) cause severe retinal degeneration. RDS and its homolog ROM-1 (rod outer segment protein 1) are synthesized in the inner segment and then trafficked into the outer segment where they function in tetramers and covalently linked larger complexes. Our goal is to identify binding partners of RDS and ROM-1 that may be involved in their biosynthetic pathway or in their function in the photoreceptor outer segment (OS). Here we utilize several methods including mass spectrometry after affinity purification, in vitro co-expression followed by pull-down, in vivo pull-down from mouse retinas, and proximity ligation assay to identify and confirm the SNARE proteins Syntaxin 3B and SNAP-25 as novel binding partners of RDS and ROM-1. We show that both covalently linked and non-covalently linked RDS complexes interact with Syntaxin 3B. RDS in the mouse is trafficked from the inner segment to the outer segment by both conventional (i.e., Golgi dependent) and unconventional secretory pathways, and RDS from both pathways interacts with Syntaxin3B. Syntaxin 3B and SNAP-25 are enriched in the inner segment (compared to the outer segment) suggesting that the interaction with RDS/ROM-1 occurs in the inner segment. Syntaxin 3B and SNAP-25 are involved in mediating fusion of vesicles carrying other outer segment proteins during outer segment targeting, so could be involved in the trafficking of RDS/ROM-1.

  • The Y141C knockin mutation in RDS leads to complex phenotypes in the mouse
    Human molecular genetics, 2014
    Co-Authors: Michael W. Stuck, Shannon M Conley, Muna I Naash
    Abstract:

    Mutations in the photoreceptor-specific gene Peripherin-2 (PRPH-2, also known as retinal degeneration slow/RDS) cause incurable retinal degeneration with a high degree of phenotypic variability. Patient phenotypes range from retinitis pigmentosa to various forms of macular and pattern dystrophy. Macular and pattern dystrophy in particular are associated with complex, poorly understood disease mechanisms, as severe vision loss is often associated both with defects in the photoreceptors, as well as the choroid and retinal pigment epithelium (RPE). Since there is currently no satisfactory model to study pattern dystrophy disease mechanisms, we generated a knockin mouse model expressing an RDS pattern dystrophy mutation, Y141C. Y141C mice exhibited clinical signs similar to those in patients including late-onset fundus abnormalities characteristic of RPE and choroidal defects and electroretinogram defects. Ultrastructural examination indicated that disc formation was initiated by the Y141C protein, but proper sizing and alignment of discs required wild-type RDS. The biochemical mechanism underlying these abnormalities was tied to defects in the normal process of RDS oligomerization which is required for proper RDS function. Y141C-RDS formed strikingly abnormal disulfide-linked complexes which were localized to the outer segment (OS) where they impaired the formation of proper OS structure. These data support a model of pattern dystrophy wherein a primary molecular defect occurring in all photoreceptors leads to secondary sequellae in adjacent tissues, an outcome which leads to macular vision loss. An understanding of the role of RDS in the interplay between these tissues significantly enhances our understanding of RDS-associated pathobiology and our ability to design rational treatment strategies.

Andrew F. X. Goldberg - One of the best experts on this subject based on the ideXlab platform.

  • Multistep Peripherin-2/rds self-assembly drives membrane curvature for outer segment disk architecture and photoreceptor viability.
    Proceedings of the National Academy of Sciences of the United States of America, 2020
    Co-Authors: Michelle L Milstein, David S Williams, Breyanna Cavanaugh, Nicole M Roussey, Stefanie Volland, Andrew F. X. Goldberg
    Abstract:

    Rod and cone photoreceptor outer segment (OS) structural integrity is essential for normal vision; disruptions contribute to a broad variety of retinal ciliopathies. OSs possess many hundreds of stacked membranous disks, which capture photons and scaffold the phototransduction cascade. Although the molecular basis of OS structure remains unresolved, recent studies suggest that the photoreceptor-specific tetraspanin, Peripherin-2/rds (P/rds), may contribute to the highly curved rim domains at disk edges. Here, we demonstrate that tetrameric P/rds self-assembly is required for generating high-curvature membranes in cellulo, implicating the noncovalent tetramer as a minimal unit of function. P/rds activity was promoted by disulfide-mediated tetramer polymerization, which transformed localized regions of curvature into high-curvature tubules of extended lengths. Transmission electron microscopy visualization of P/rds purified from OS membranes revealed disulfide-linked tetramer chains up to 100 nm long, suggesting that chains maintain membrane curvature continuity over extended distances. We tested this idea in Xenopus laevis photoreceptors, and found that transgenic expression of nonchain-forming P/rds generated abundant high-curvature OS membranes, which were improperly but specifically organized as ectopic incisures and disk rims. These striking phenotypes demonstrate the importance of P/rds tetramer chain formation for the continuity of rim formation during disk morphogenesis. Overall, this study advances understanding of the normal structure and function of P/rds for OS architecture and biogenesis, and clarifies how pathogenic loss-of-function mutations in P/rds cause photoreceptor structural defects to trigger progressive retinal degenerations. It also introduces the possibility that other tetraspanins may generate or sense membrane curvature in support of diverse biological functions.

  • Peripherin diverts ciliary ectosome release to photoreceptor disc morphogenesis
    The Journal of cell biology, 2017
    Co-Authors: Robert S. Molday, Andrew F. X. Goldberg
    Abstract:

    Formation of membrane discs in photoreceptor cells requires evagination of its ciliary plasma membrane by an unknown molecular mechanism. Salinas et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201608081) show that Peripherin (also known as Peripherin-2 or Peripherin-2/rds) diverts membrane traffic to photoreceptor disc formation by inhibiting ectosome release from the cilium.

  • An inducible amphipathic helix within the intrinsically disordered C terminus can participate in membrane curvature generation by Peripherin-2/rds.
    The Journal of biological chemistry, 2017
    Co-Authors: Michelle L Milstein, Victoria A. Kimler, Chiranjib Ghatak, Alexey S. Ladokhin, Andrew F. X. Goldberg
    Abstract:

    Peripherin-2/rds is required for biogenesis of vertebrate photoreceptor outer segment organelles. Its localization at the high-curvature rim domains of outer segment disk membranes suggests that it may act to shape these structures; however, the molecular function of this protein is not yet resolved. Here, we apply biochemical, biophysical, and imaging techniques to elucidate the role(s) played by the protein's intrinsically disordered C-terminal domain and an incipient amphipathic α-helix contained within it. We investigated a deletion mutant lacking only this α-helix in stable cell lines and Xenopus laevis photoreceptors. We also studied a soluble form of the full-length ˜7-kDa cytoplasmic C terminus in cultured cells and purified from Escherichia coli. The α-helical motif was not required for protein biosynthesis, tetrameric subunit assembly, tetramer polymerization, localization at disk rims, interaction with GARP2, or the generation of membrane curvature. Interestingly, however, loss of the helical motif up-regulated membrane curvature generation in cellulo, introducing the possibility that it may regulate this activity in photoreceptors. Furthermore, the incipient α-helix (within the purified soluble C terminus) partitioned into membranes only when its acidic residues were neutralized by protonation. This suggests that within the context of full-length Peripherin-2/rds, partitioning would most likely occur at a bilayer interfacial region, potentially adjacent to the protein's transmembrane domains. In sum, this study significantly strengthens the evidence that Peripherin-2/rds functions directly to shape the high-curvature rim domains of the outer segment disk and suggests that the protein's C terminus may modulate membrane curvature-generating activity present in other protein domains.

  • molecular basis for photoreceptor outer segment architecture
    Progress in Retinal and Eye Research, 2016
    Co-Authors: Andrew F. X. Goldberg, Orson L Moritz, David S Williams
    Abstract:

    Abstract To serve vision, vertebrate rod and cone photoreceptors must detect photons, convert the light stimuli into cellular signals, and then convey the encoded information to downstream neurons. Rods and cones are sensory neurons that each rely on specialized ciliary organelles to detect light. These organelles, called outer segments, possess elaborate architectures that include many hundreds of light-sensitive membranous disks arrayed one atop another in precise register. These stacked disks capture light and initiate the chain of molecular and cellular events that underlie normal vision. Outer segment organization is challenged by an inherently dynamic nature; these organelles are subject to a renewal process that replaces a significant fraction of their disks (up to ∼10%) on a daily basis. In addition, a broad range of environmental and genetic insults can disrupt outer segment morphology to impair photoreceptor function and viability. In this chapter, we survey the major progress that has been made for understanding the molecular basis of outer segment architecture. We also discuss key aspects of organelle lipid and protein composition, and highlight distributions, interactions, and potential structural functions of key OS-resident molecules, including: kinesin-2, actin, RP1, prominin-1, protocadherin 21, Peripherin-2/rds, rom-1, glutamic acid-rich proteins, and rhodopsin. Finally, we identify key knowledge gaps and challenges that remain for understanding how normal outer segment architecture is established and maintained.

  • Membrane curvature generation by a C-terminal amphipathic helix in Peripherin-2/rds, a tetraspanin required for photoreceptor sensory cilium morphogenesis
    Journal of Cell Science, 2013
    Co-Authors: Nidhi Khattree, Linda M. Ritter, Andrew F. X. Goldberg
    Abstract:

    Vertebrate vision requires photon absorption by photoreceptor outer segments (OSs), structurally elaborate membranous organelles derived from non-motile sensory cilia. The structure and function of OSs depends on a precise stacking of hundreds of membranous disks. Each disk is fully (as in rods) or partially (as in cones) bounded by a rim, at which the membrane is distorted into an energetically unfavorable high-curvature bend; however, the mechanism(s) underlying disk rim structure is (are) not established. Here, we demonstrate that the intrinsically disordered cytoplasmic C-terminus of the photoreceptor tetraspanin Peripherin-2/rds (P/rds) can directly generate membrane curvature. A P/rds C-terminal domain and a peptide mimetic of an amphipathic helix contained within it each generated curvature in liposomes with a composition similar to that of OS disks and in liposomes generated from native OS lipids. Association of the C-terminal domain with liposomes required conical phospholipids, and was promoted by membrane curvature and anionic surface charge, results suggesting that the P/rds C-terminal amphipathic helix can partition into the cytosolic membrane leaflet to generate curvature by a hydrophobic insertion (wedging) mechanism. This activity was evidenced in full-length P/rds by its induction of small-diameter tubulovesicular membrane foci in cultured cells. In sum, the findings suggest that curvature generation by the P/rds C-terminus contributes to the distinctive structure of OS disk rims, and provide insight into how inherited defects in P/rds can disrupt organelle structure to cause retinal disease. They also raise the possibility that tethered amphipathic helices can function for shaping cellular membranes more generally.