Human Usher syndrome is a severe and congenital form of syndromic deafness that affects 1 person in 25,000 people in the world population. Normally the stereocilia, microvillar protrusions of the apical membrane of inner ear hair cells, are organized into coherent bundles. This precise organization is critical for mechanosensing, i.e. for hearing. Mutation in any of the five known Usher syndrome genes is sufficient to alter the precise organization of stereocilia, a condition that results in deafness. To date, however, the molecular mechanisms responsible for the splaying of stereocilia and genesis of the disease are not well understood. Here, I identified Drosophila melanogaster genes related to human Usher syndrome and characterized some of them (Cad99C, DSANS and crinkled) during Drosophila development, in the processes of microvilli morphogenesis in the follicular and wing imaginal disc epithelia. Cadherin Cad99C is a transmembrane protein with putative cell adhesion properties. Similar to its human ortholog Protocadherin 15, Drosophila Cad99C localizes to microvillar protrusions in the follicular epithelium. In this epithelium, Cad99C is required for the proper morphogenesis and organization of microvilli into bundles, similar to human Protocadherin 15. Further, overexpression of the full-length Cad99C or of a deleted version, devoid of the cytoplasmic region, promotes microvilli bundling. This finding suggests that Cad99C establishes adhesive interactions between microvilli via its extracellular region. Interestingly, morphological alteration of follicle cell microvilli associates with defective deposition of the vitelline membrane, an extracellular matrix that protects the embryo from osmotic stresses. These findings suggest that microvilli are normally required for the even deposition of the extracellular matrix. In order to test whether Cad99C is involved in microvilli morphogenesis and bundling in other tissues, I analyzed the function of Cad99C in a larval tissue, the wing imaginal disc. Cad99C overexpression, but not Cad99C removal, is sufficient to alter microvilli morphology and organization in the columnar epithelium of the wing imaginal disc. Likely, other molecules can compensate for Cad99C loss of function in this tissue. To possibly get some insights on the molecular function of other Usher syndrome proteins, I analyzed the function of Drosophila SANS and crinkled in the follicular epithelium, where both these genes are expressed. crinkled is the ortholog of myosinVIIa, that encodes a motor protein of the actin cytoskeleton. DSANS is related to human SANS and encodes a cytoplasmic protein of unknown function. It has been puzzling how removal of SANS, a cytoplasmic protein, could impair adhesion and bundling of stereocilia. To study the function of DSANS, I generated null mutant flies and observed that, in the absence of DSANS, delivery of Cad99C to microvilli is impaired. Cad99C localization is however unperturbed in crinkled mutant follicle cells. By immunostaining, DSANS immunoreactivity was detected diffusively in the cytoplasm and in dot-like structures, possibly corresponding to vesicles. In conclusion, DSANS is a cytoplasmic protein that is required for the efficient delivery of Cad99C to microvilli protrusions. Taken together, the analysis that I here performed of Drosophila Usher syndrome related genes indicates two novel molecular mechanisms of function for the corresponding human Usher syndrome proteins. First, human Protocadherin 15, like Drosophila Cad99C, could be involved in establishing adhesive interactions between microvilli protrusions of the inner ear (stereocilia). Removal of Protocadherin 15 would then cause splaying of stereocilia due to lack of inter-stereocilia adhesive links. Second, the analysis here performed suggests that SANS is involved in the efficient delivery of Protocadherin 15 to stereocilia. Mutations in SANS would then lead to splaying of stereocilia and deafness due to poor localization of Protocadherin 15 to stereocilia.

In my thesis I will discuss Edgar Allan Poe’s “The Fall of the House of Usher” in relation to the expectations that scholars have of the gothic genre. I will break this project into four chapters, along with an introduction: (Ch.1) a critical review of scholarship on Poe’s “Usher” that will demonstrate the difficulty in coming to a critical consensus on the tale, (Ch.2) a discussion of Brown’s outline of Gothic conventions, (Ch.3) a look at Poe’s “The Philosophy of Composition” juxtaposed with Aristotle’s Poetics to illumine aspects of Poe’s approach to writing and how it has been informed, and (Ch.4) a close reading of Poe’s “Usher.”

Den här uppsatsen handlar om elever med Ushers syndrom och inkludering i klassrummet. Ushers syndrom består av en kombinerad syn- och hörselnedsättning och synen försämras med tiden framförallt i synfältet. Med Ushers syndrom innebär det även svårigheter att se i mörkret. Syftet med uppsatsen är att undersöka hur inkludering kan skapas i klassrummet utifrån elever på aktörsnivå och skolan och lärare på institutionell nivå. Anpassningarna är viktiga faktorer för att eleverna ska bli inkluderade och jag undersöker även vilka anpassningar som uppstår och hur går de tillväga för att lösa problem i klassrummet. Denna uppsats utgår från en etnografisk ansats och studiens empiri består av intervjuer med elever, läraren, dövblindsamordnaren, en klassrumsobservation och styrdokument. Dessa empirier presenteras i resultatredovisningen med fokus på elever med Ushers syndrom och inkludering på olika nivåer som skolan, läraren och klassrummet. Studien har visat att skolan och lärarens bemötande är en betydande faktor för inkluderingsprocessen. Forskningen har betonat att det är hela verksamheten som ska förändras i ett inkluderingsarbete. Ett bra bemötande innebär att dessa aktörer med anpassningar ser till att eleverna med Ushers syndrom får uppleva inkludering. Anpassningarna som visats i studien är lärarens klädsel, belysning, turtagning i samtal och tekniska hjälpmedel. Det har konstaterats att elever med Ushers syndrom också själva har en del i inkluderingsarbetet genom att framföra sina behov eftersom behovet varierar från elev till elev. Det har framträtt i studien att det inte är lätt att framföra sina behov direkt eftersom elever inte vill avvika från normen i klassrummet som består av döva elever och teckenspråk.

This qualitative study investigated the remembered lived experiences of six individuals who were diagnosed with Usher syndrome, the effect that the progressive condition had upon their lives, and their experiences with vocational rehabilitation. Usher syndrome is an autosomal recessive condition that presents as deafness or hearing loss with comorbid retinitis pigmentosa sometimes with vestibular areflexia. The participants recalled details of their own reaction to the diagnoses as well as the reactions of their parents. Themes were identified in their responses that included independent dependence, Usher support, parental reaction, lowered expectations, hope, and ongoing change. The participants, three men and three women, reported periods of adjustment and sadness as well as hopes for their future, career accomplishments, and social interactions.

Thesis (M.S.)--State University of Wisconsin at La Crosse.

Le syndrome de Usher (USH) est une maladie transmise selon le mode autosomique récessif caractérisée par l’association d’une surdité congénitale (HL) et d’une rétinite pigmentaire (RP), et dans certains cas, d’une aréflexie vestibulaire. Une hétérogénéité clinique et génétique est reconnue. Environ 10 % des cas USH restent non résolus après analyse moléculaire exhaustive des différents gènes. Ces cas incluent les patients qui ne portent aucune mutation dans un des gènes USH connus ainsi que les patients porteurs d’une seule mutation dans un gène USH. Au cours de cette thèse, nous nous sommes intéressés à l’étude des patients porteurs d’une seule mutation dans les gènes USH2A et PCDH15.Dans la première partie de la thèse, nous avons analysé une cohorte de patients avec un phénotype USH2A bien défini : 5 patients pour lesquels une seule mutation à l’état hétérozygote avait été identifiée dans le gène USH2A et un patient porteur d’un variant silencieux en trans d’une mutation non-sens.Pour les 5 patients, nous avons émis l’hypothèse que la seconde mutation, restant à être identifiée, pourrait se trouver dans des régions introniques profondes. Pour cela, nous avons développé une approche de séquençage à haut débit (NGS) de l’ADN pour identifier les variants introniques profonds dans le gène USH2A et évaluer leurs conséquences sur l’épissage. Comme preuve de concept et pour valider l’approche, y compris le pipeline bio-informatique et l’évaluation des outils de prédiction de l’épissage, nous avons analysé un patient porteur d’un pseudoexon (PE) connu dans le gène USH2A. Ensuite, les 5 patients ont été étudiés en utilisant le pipeline défini, ce qui a conduit à l’identification de 3 nouveaux variants introniques profonds chez 4 d’entre eux. Tous les variants ont été prédits comme pouvant avoir un impact sur l’épissage et aboutir à l’insertion de PE. Ces prédictions ont été validées par les essais minigènes. Grâce à cette étude, nous présentons une stratégie innovante pour identifier les mutations introniques profondes, lorsque l’analyse des transcrits n’est pas possible. Par ailleurs, le pipeline bio-informatique développé fonctionne indépendamment de la taille du gène analysé, ce qui permet l’application possible de cette approche à n’importe quel gène. Par ailleurs, un oligonucléotide antisens de type morpholino (AMO) a été évalué in vitro afin de rétablir l’altération d’épissage induite par une des mutations identifiées. Les résultats ont montré un taux d’exclusion élevé du transcrit aberrant et suggèrent une application possible en thérapie moléculaire. Nous avons ensuite effectué des études sur le variant USH2A c.1377T>A, un variant silencieux afin d’évaluer son effet sur l’épissage. L’analyse de l’ARN issu de cellules nasales du patient a montré que ce variant conduit au saut de l’exon 8 dans les transcrits USH2A. Ceci a été confirmé par un essai minigène. En outre, des études préliminaires ont été réalisées en utilisant des outils de prédictions et des essais minigènes pour évaluer l’implication des éléments cis-régulateurs dans le défaut d’épissage observé chez le patient. Dans la deuxième partie de la thèse, nous avons analysé une patiente USH1, pour laquelle une seule mutation avait été identifiée dans le gène PCDH15. Dans ce cas, nous avons combiné la culture des cellules épithéliales nasales avec l’analyse des transcrits PCDH15. Celle-ci a été réalisée par séquençage de cinq RT-PCR chevauchantes. Grâce à cette analyse, nous avons réussi à délimiter une région d’intérêt dans le transcrit, dont l’amplification a échoué exclusivement pour l’allèle porteur de la mutation non identifiée. D’autres analyses ont été effectuées dans la région génomique correspondante par capture ciblée couplée au séquençage NGS et LongRange PCR suivi de séquençage Sanger. Cependant, aucun variant candidat n’a été identifié à ce jour. Nous suggérons l’implication de mécanismes moléculaires complexes qui restent à être caractérisés. / Usher syndrome (USH) is an autosomal recessive disorder characterized by the association of sensorineural hearing loss (HL) and retinitis pigmentosa (RP), and in some cases, vestibular areflexia. Clinical and genetic heterogeneity are recognised. Indeed, three clinical types can be caused by mutations in one of the 10 known genes and USH2A represents the most frequently involved gene.Approximately 10 % of the USH cases remain genetically unsolved after extensive molecular analysis of the different genes, which includes sequencing of the exons and their intronic boundaries, combined to large rearrangements screening by array CGH. These unsolved cases include patients who do not carry any mutation in any of the known USH genes and patients who carry a single USH mutation. During this thesis we focalised on the study of patients carrying a single mutation in USH2A and PCDH15 gene.First, we have analysed a cohort of well-defined USH2A patients: five patients, for whom a single USH2A heterozygous mutation had been identified and one patient carrying a silent variant in trans to a nonsense mutation. For the 5 patients, we supposed that the second mutation remaining to be found could be localised deep in the introns. Indeed, a deep intronic mutation resulting in the inclusion of a pseudoexon (PE 40) in USH2A transcripts had been identified, following RNA analysis from nasal cells. Unfortunately, analysing USH2A transcripts still represent a challenging approach in a diagnostic settings and it is not always possible. To circumvent this issue, we have developed a DNA-Next Generation Sequencing (NGS) approach to identify deep intronic variants in USH2A and evaluate their consequences on splicing. As a proof of concept and to validate this approach, including the bioinformatics pipeline and the assessment of splicing predictor tools, the patient carrying the PE 40 was analysed at first. Then, the 5 patients were studied using the defined pipeline, which led to the identification of 3 distinct novel deep intronic variants in 4 of them. All were predicted to affect splicing and resulted in the insertion of PEs, as shown by minigene assays. Through this study, we present a new and attractive strategy to identify deep intronic mutations, when RNA analyses are not possible. In addition, the bioinformatics pipeline developed is independent of the gene size, implying the possible application of this approach to any disease-linked gene. Moreover, an antisense morpholino oligonucleotide (AMO) tested in vitro for its ability to restore the splicing alterations caused by one of the identified mutation provided high inhibition rates. These results are indicative of a potential application for molecular therapy.In the second case, we have performed studies on the USH2A c.1377T>A silent variant to investigate its effect on splicing. Analysis of RNA from nasal cells of patients showed that this variant led to the skipping of exon 8 in USH2A transcripts. This was confirmed by minigene assay. Moreover, preliminary studies have been performed using prediction tools and minigene assays to assess the involvement of cis-acting elements in causing the aberrant splicing.In the second part of the thesis, we have analysed an USH1 patient, for whom only one mutation had been identified in the PCDH15 gene. In this case, we combined nasal epithelial cells culture with the analysis of the PCDH15 transcripts. This was performed by sequencing five overlapping RT-PCRs. Through this analysis, we were able to delimit a region within the transcript, which failed to be amplified exclusively in the allele carrying the unidentified mutation. Further analyses have been performed in the corresponding genomic region by NGS-target capture and LongRange PCR associated with Sanger sequencing. However, no evident mutation has been identified so far. Therefore, we suggest the involvement of complex molecular mechanisms that remain to be characterised.

La vue et l'ouïe font intervenir des cellules capables de rapidement traduire une onde, lumineuse ou sonore, en un message électrochimique transmissible au cerveau. La fonction de ces cellules sensitives repose sur leurs morphologies uniques. Les mutations de onze gènes sont la cause des syndromes Usher, associant cécité et surdité. Les protéines Usher sont indispensables à l'architecture de ces deux types cellulaires ; elles forment des complexes dont les interactions clés sont maintenues principalement par des domaines PDZ. L'une des protéines centrales de ce réseau est la Whirline, une protéine multi-domaine contenant trois domaines PDZ. Pour comprendre les bases moléculaires des syndromes Usher, nous nous sommes concentrés sur la caractérisation biochimique et biophysique de la Whirline. Nous avons identifié un nouveau domaine HHD2 de la Whirline dont nous avons obtenue la structure à haute résolution et déterminé le comportement en solution, isolé et avec les domaines adjacents. Nous avons ensuite caractérisé un supramodule transitoire entre deux domaines PDZ, maintenu par des extensions structurées de chacun des domaines. Nous avons résolu la structure de la conformation compacte unique de ce complexe et étudié son équilibre avec un ensemble de conformations étendues. Nous avons enfin caractérisé in vitro le réseau d'interaction des domaines PDZ de la Whirline avec les protéines Usher. L'ensemble de nos résultats sur la structure modulaire et l'interactome de la Whirline permet de mieux comprendre le rôle de la Whirline dans les différents complexes Usher et d'expliquer les conséquences de ses mutations sur les mécanismes moléculaires de l'audition et de la vision. / Vision and hearing rely on the capacity of cells to rapidly transduce electromagnetic waves or sound waves into chemical messages that are transmissible to the brain. The function of these sensory cells requires unique morphologies. The mutations of eleven genes are responsible for Usher syndromes, associating blindness and deafness. The Usher proteins are pivotal to the architecture of the photoreceptor and hearing cells. They form complexes in which the critical interactions are mainly maintained by PDZ domains. One of these central proteins is Whirlin, a multi-domain protein encompassing three PDZ domains. To understand the molecular basis of the Usher syndromes, we focused our project on the biochemical and biophysical characterization of Whirlin. We identified a new HHD2 domain on Whirlin, for which we solved the structure at high resolution and determined the behavior in solution, isolated or with adjacent domains. We then identified a transient supramodule between two PDZ domains, maintained by PDZ structured extensions. We determined the structure of the compact and unique conformation of this tandem and we characterized its equilibrium with an ensemble of more extended conformations. Finally, we characterized in vitro the network of interaction of the PDZ domains of Whirlin, with the majority of the Usher proteins. Our results on the modular structure and the interactome of Whirlin get insight into the role of Whirlin in the numerous complexes formed by the Usher proteins and allow to better explain the consequences of its mutation on the molecular mechanisms of hearing and vision.

Le syndrome d’Usher (USH) cause une surdité-cécité chez l’homme. Au moins neuf gènes responsables ont été identifiés. L’origine de l’atteinte auditive a été dévoilée par l’analyse de souris mutantes, mais les causes de la cécité sont encore obscures. Néanmoins, unes des protéines de Usher, la myosine VIIa, a été impliquée dans le transport intracellulaire dans les photorécepteurs. Pour mieux comprendre le rôle dans la rétine, j’ai étudié l’un de ses partenaires, la spectrine βV. Nous avons conclu que cette spectrine, en collaboration avec les protéines USH1, est impliquée dans le trafic cellulaire: elle couple les moteurs (myosine VIIA, kinesine II et le complexe dynéine/dynactine) à leurs cargos en route vers le segment externe des photorécepteurs. La combinaison d’études comparatives dans les cellules ciliées (CC) de l'oreille interne de grenouille et de souris, de tests biochimiques et d’analyses phylogénétiques indique que le transport vers et depuis la surface apicale des cellules est la fonction ancestrale de cette spectrine. Chez les mammifères, une pression évolutive a engendré le recrutement de la spectrine βV à la paroi latérale des CC externes auditives, probablement pour participer à une nouvelle fonction: l’électromotilité. Enfin, j’ai étudié l’origine de la surdité dans le syndrome d’Usher III. Le seul gène causal connu est CLRN1, qui code pour la clarine-1. Nous avons conclu que la clarine-1 est nécessaire à la maturation et le maintien des touffes ciliaires des CC. De plus, la clarine-1 est essentielle pour le regroupement des canaux calciques voltage-dépendants au voisinage immédiat de la machinerie exocytotique de la synapse à ruban des CC internes. / Usher syndrome (USH) causes a combined deafness-blindness in humans. At least nine causative genes are known. While the analysis of USH knockout mice has shed light on the origin of the auditory deficit, the causes of vision loss are still unclear. Nevertheless, USH1B protein, myosin VIIa, appears to contribute to intracellular traffic in photoreceptor cells. To better understand the role of this myosin in the retina, I studied the functions of its interacting partner, spectrin βV. We found that spectrin V, along with USH1 proteins, participates in intracellular transport by coupling motor proteins (myosin VIIa, kinesin II, dynein/dynactin complex) to the cargoes en route towards the outer segment of photoreceptor cells. Evidence from comparative studies in frog and mouse inner ear, biochemical assays and phylogenetic analyses point to cargo trafficking to and from the apical cell region, as the likely ancestral function of this spectrin. Our analyses also suggest that evolutionary pressures in the mammalian lineage drove the recruitment of spectrin βV to the lateral wall of auditory outer hair cells, probably to support a new function: electromotility. Finally, I explored the origin of hearing loss in Usher syndrome of type III (USH3). So far, the only causal gene known is CLRN1, which codes for clarin-1. The comparative characterization of two Clrn1 mouse mutants revealed that clarin-1 is required for the maturation and maintenance of the hair bundle in the hair cells. Moreover, our results indicate that clarin-1 is also essential to cluster the voltage-gated Ca2+ channels in close proximity to the exocytotic machinery of the ribbon synapse of inner hair cells.

Human Usher syndrome is a severe and congenital form of syndromic deafness that affects 1 person in 25,000 people in the world population. Normally the stereocilia, microvillar protrusions of the apical membrane of inner ear hair cells, are organized into coherent bundles. This precise organization is critical for mechanosensing, i.e. for hearing. Mutation in any of the five known Usher syndrome genes is sufficient to alter the precise organization of stereocilia, a condition that results in deafness. To date, however, the molecular mechanisms responsible for the splaying of stereocilia and genesis of the disease are not well understood. Here, I identified Drosophila melanogaster genes related to human Usher syndrome and characterized some of them (Cad99C, DSANS and crinkled) during Drosophila development, in the processes of microvilli morphogenesis in the follicular and wing imaginal disc epithelia. Cadherin Cad99C is a transmembrane protein with putative cell adhesion properties. Similar to its human ortholog Protocadherin 15, Drosophila Cad99C localizes to microvillar protrusions in the follicular epithelium. In this epithelium, Cad99C is required for the proper morphogenesis and organization of microvilli into bundles, similar to human Protocadherin 15. Further, overexpression of the full-length Cad99C or of a deleted version, devoid of the cytoplasmic region, promotes microvilli bundling. This finding suggests that Cad99C establishes adhesive interactions between microvilli via its extracellular region. Interestingly, morphological alteration of follicle cell microvilli associates with defective deposition of the vitelline membrane, an extracellular matrix that protects the embryo from osmotic stresses. These findings suggest that microvilli are normally required for the even deposition of the extracellular matrix. In order to test whether Cad99C is involved in microvilli morphogenesis and bundling in other tissues, I analyzed the function of Cad99C in a larval tissue, the wing imaginal disc. Cad99C overexpression, but not Cad99C removal, is sufficient to alter microvilli morphology and organization in the columnar epithelium of the wing imaginal disc. Likely, other molecules can compensate for Cad99C loss of function in this tissue. To possibly get some insights on the molecular function of other Usher syndrome proteins, I analyzed the function of Drosophila SANS and crinkled in the follicular epithelium, where both these genes are expressed. crinkled is the ortholog of myosinVIIa, that encodes a motor protein of the actin cytoskeleton. DSANS is related to human SANS and encodes a cytoplasmic protein of unknown function. It has been puzzling how removal of SANS, a cytoplasmic protein, could impair adhesion and bundling of stereocilia. To study the function of DSANS, I generated null mutant flies and observed that, in the absence of DSANS, delivery of Cad99C to microvilli is impaired. Cad99C localization is however unperturbed in crinkled mutant follicle cells. By immunostaining, DSANS immunoreactivity was detected diffusively in the cytoplasm and in dot-like structures, possibly corresponding to vesicles. In conclusion, DSANS is a cytoplasmic protein that is required for the efficient delivery of Cad99C to microvilli protrusions. Taken together, the analysis that I here performed of Drosophila Usher syndrome related genes indicates two novel molecular mechanisms of function for the corresponding human Usher syndrome proteins. First, human Protocadherin 15, like Drosophila Cad99C, could be involved in establishing adhesive interactions between microvilli protrusions of the inner ear (stereocilia). Removal of Protocadherin 15 would then cause splaying of stereocilia due to lack of inter-stereocilia adhesive links. Second, the analysis here performed suggests that SANS is involved in the efficient delivery of Protocadherin 15 to stereocilia. Mutations in SANS would then lead to splaying of stereocilia and deafness due to poor localization of Protocadherin 15 to stereocilia.

Retinitis Pigmentosa (RP) refers to a group of inherited retinal dystrophies resulting from progressive photoreceptor degeneration and accumulation of intra-retinal pigment-like deposits. X-linked forms of RP are frequently caused by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. The RPGR transcript undergoes complex alternative splicing to express both constitutive (RPGR^ex1-19) and RPGR^ORF15 variants. Although RPGR is thought to play a role in ciliary function, little is known about the physiological significance of expressing two distinct groups of variants. This study compares Rpgr^ex1-19 and Rpgr^ORF15 expression in developing photoreceptors using immunoblot analysis and immunohistochemistry, assesses ciliary affinity in adult photoreceptors by protein fractionation, examines Rpgr function in transgenic mouse models and identifies a novel Rpgr^ORF15 binding partner using a yeast two-hybrid screen. Our data reveal that Rpgr expression undergoes dynamic temporal regulation during retinal development and indicates variability in ciliary localization of Rpgr variants in adult photoreceptors. Utilization of distinct Rpgr variants during stages of photoreceptor development suggests independent roles. Further examination of Rpgr function using transgenic mouse models over-expressing either the Rpgr^ex1-19 or Rpgr^ORF15 variant reveals that despite normal ciliary localization, an excess of RPGR^ex1-19 results in atypical accumulation of Rpgr in photoreceptor outer segments, abnormal photoreceptor morphology and severe retinal degeneration. The data indicate that the constitutive variant cannot substitute for Rpgr function in photoreceptors and suggest that proper maintenance of the Rpgr isoform ratio is critical to photoreceptor viability. Using mouse retinal cDNA in a yeast two-hybrid screen with the C-terminus of the Rpgr^ORF15 variant, we identified a novel variant of whirlin as an interacting partner. Mutations in whirlin result in Usher syndrome, a disorder characterized by hearing loss and RP. RT-PCR and immunoblot analysis were used to confirm the presence of selected candidate partners in the retina and interaction was confirmed by pull-down assays and co-immunoprecipitation from retinal homogenate. Immunohistochemistry showed co-localization of RPGR and whirlin within photoreceptors and identified isoform specific localization of whirlin. These findings indicate that whirlin binds Rpgr^ORF15 and that this novel isoform may be required for photoreceptor function, thus providing a potential mechanism for the RP phenotype observed in Usher syndrome.