Basile Tarchini - US grants

PROJECT SUMMARY The funds requested in this application are for partial support of the ?Modeling Hearing and Balance Disorders in Mice: The HEar@JAX Workshop?, to be held at The Jackson Laboratory (JAX) in Bar Harbor, Maine, September 23-28, 2018. This hands-on workshop is one of a kind as it focuses on mouse models of human auditory and vestibular disorders. It represents an intensive training opportunity for 20 graduate students, postdocs and investigators wishing to gain expertise in the biology and functional characterization of the mouse auditory and vestibular systems. The course is structured with classroom lectures in the morning, followed by hands-on laboratory sessions and tutorials in the afternoon. Evening lectures will feature plenary presentations by senior researchers in the field. Participants will also have the opportunity to present their own research and there will be dedicated time for discussions of potential career opportunities. Six members of the organizing committee, three Jackson Laboratory speakers and ten invited faculty who all committed to participate pending funding will give the lectures and the laboratory training. During hands-on laboratory sessions, participants will learn how to dissect the cochlea and the vestibular organs and perform whole-mount immunofluorescence stainings using typical antibodies to label hair cells, supporting cells and neuron projections. The sensory organs will also be placed in culture to perform dye uptake and show aminoglycoside toxicity in hair cells. Cochlear and vestibular samples collected by participants will be mounted and observed using confocal microscopy. Mutant samples prepared in advance will enable participants to observe phenotypes leading to congenital hearing loss and circling behavior. Finally, tutorials and demonstrations will be presented on various topics including inner ear paint-fill, physiology (Auditory brainstem response and Distortion product otoacoustic emission recordings) and therapy (Organoids, Inner ear gene transfer). One of the hallmarks of this workshop is the opportunity for participants to closely interact with the faculty at the Highseas Conference Center, which also serves as the residence and dining facility for attendees. Having meals together as well as other social activities encourages network development and fosters collaboration. Invited speakers: Uli Muller (Johns Hopkins), Karen Steel (King's college), Neil Segil (USC), Ronna Hertzano (U of Maryland), Uri Manor (Salk Institute), Jennifer Stone (U of Washington), Paul Fuchs (Johns Hopkins), Andy Groves (Baylor), Gwen Geleoc (Boston Children's hospital), Karl Koehler (Indiana U). Organizers: Karen Avraham (Tel-Aviv U), Matt Kelley (NIH), Guy Richardson (U of Sussex), Amanda Lauer (Johns Hopkins), Mike Bowl (MRC Harwell), Basile Tarchini (The Jackson Laboratory).

PROJECT SUMMARY/ABSTRACT This proposal addresses the uncharacterized role of the mInsc-LGN-G?i protein complex in stereocilia elongation, and defines LGN-G?i as a long sought-after cargo of Myo15 required for differential stereocilia growth across rows during hair cell development. In the absence of LGN or G?i, postnatal stereocilia are stunted and form an immature-looking bundle that only retains a shallow staircase pattern. Interestingly, very similar defects have been reported in the absence of Myo15, Whirlin and Eps8, three proteins enriched at the tips of all stereocilia in amounts proportional to their height. We show here that LGN and G?i share the same tip localization, but are restricted to the first stereocilia row. Strikingly, LGN and G?i fail to traffic to tips in absence of Myo15. In contrast, Myo15-Whrn-Eps8 are found in similar low amounts across all stunted rows in LGN or G?i mutants, suggesting that LGN-G?i instruct differential stereocilia identity across rows by specifying the first row. By intercrossing mutants and using genetics, protein immunolocalization and protein binding biochemistry, we propose to solve the function of an extended Myo15 complex now including LGN-G?i where all proteins apparently have independent, complementary functions to shape the bundle. We previously showed that mInsc-LGN-G?i first occupy and generate the 'bare zone', the flat region of the hair cell apex where early microvilli exclusion outlines the V-shaped or semi-circular edge of the forming bundle. Based on evidence for dynamic and balanced LGN-G?i protein amounts between subcellular compartments, we propose that restriction of LGN-G?i to the first row could be instructed by their prior enrichment at the adjacent bare zone. LGN-G?i would promote higher amounts of Myo15-Whrn-Eps8 at the first row, its growth into the tallest row in turn influencing the height of shorter rows via oblique tip-links, as proposed previously. To test the novel idea that the staircase pattern is established by recycling planar polarity information, we propose stage-specific loss- and gain-of-function approaches, including exploratory experiments using cochlear explants aimed at elucidating and manipulating LGN-G?i function at the subcellular level. The staircase-like architecture of the hair bundle is essential for hearing and considered instrumental for direction-sensitivity to sound stimuli, but remains largely unexplained at the molecular level. By uncovering new members of the Myo15 complex and clarifying how asymmetry of growth is created across rows, this work notably improves our understanding of hereditary hearing loss in DFNB3 (MYO15), DFNB31/USH2D (WHRN), DFNB102 (EPS8) and DFNB82/Chudley-McCullough syndrome (LGN/GPSM2).

PROJECT SUMMARY/ABSTRACT Vestibular disorders affect as many as 35% of adults past age 40. Studies of the vestibular inner ear have yielded important insights into how we process and compensate for head motion including the existence of parallel channels of information in the afferent nerve. In macular organs, for example, two populations of hair cells adopt opposite planar orientations of their hair bundles and thus opposite responses to head movements. This highly conserved bidirectional organization was first described in neuromasts, the lateral line organs sensing water movements in fish, but the genetic program implementing this reversal during development is only starting to be deciphered. Consequently, ablation studies to reveal the importance of reversal for vestibular function have not been possible until recently. Here we propose to address this question by investigating the consequences of inactivating an orphan G protein coupled receptor (GPCRx), implicated by our preliminary data in orientation reversal in mouse hair cell epithelia. Based on our preliminary data, we suggest that mouse GPCRx functions downstream of the transcription factor EMX2 and upstream of the heterotrimeric G protein G?i to reverse a ground state of polarity established by planar cell polarity proteins. We will test this hypothesis and also use the GPCRx mutant as an animal model to pinpoint how polarity reversal shapes macular organ responses and downstream effects on vestibular behaviors. To reach these goals, we will: 1) Use genetics to determine how GPCRx instructs reversal at the molecular level, solving its epistatic relationship to EMX2, G?i and planar cell polarity proteins in mice, and use zebrafish to test whether GPCRx-G?i is a conserved effector pathway for reversal. 2) Use molecular markers, electrophysiology and calcium imaging to resolve hair cell maturation and function in absence of polarity reversal. 3) Determine how polarity reversal affects afferents' organization and function, with afferent recordings, as well as overall vestibular function using behavioral tests. Our coherent body of preliminary evidence ensures the feasibility and the high interest of the project, and our focus on a virtually unstudied receptor protein guarantees innovation. The multi-PI team is ideally suited to address complementary questions in both the mouse and zebrafish acoustico-lateralis systems. We anticipate that this collaborative effort will be decisive towards solving the mechanism of hair cell orientation reversal, its conservation across vertebrates and its significance for mammalian vestibular physiology. Thorough understanding of polarity reversal will help interpret and design treatments for vestibular dysfunctions.