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1.  Stereocilin-deficient mice reveal the origin of cochlear waveform distortions 
Nature  2008;456(7219):255-258.
Although the cochlea is an amplifier and a remarkably sensitive and finely tuned detector of sounds, it also produces conspicuous mechanical and electrical waveform distortions1. These distortions reflect non-linear mechanical interactions within the cochlea. By allowing one tone to suppress another (masking effect), they contribute to speech intelligibility2. Tones can also combine to produce sounds with frequencies not present in the acoustic stimulus3. These sounds compose the otoacoustic emissions that are extensively used to screen hearing in newborns. As both cochlear amplification and distortion originate from the outer hair cells, one of the two types of sensory receptor cells, it has been speculated that they stem from a common mechanism. Here, the non-linearity underlying cochlear waveform distortions is shown to rely on the presence of stereocilin, a protein defective in a recessive form of human deafness4. Stereocilin was detected in association with horizontal top connectors5-7, lateral links that join adjacent stereocilia within the outer hair cell’s hair bundle, and these links were absent in stereocilin-null mutant mice. These mice become progressively deaf. At the onset of hearing, however, their cochlear sensitivity and frequency tuning were almost normal, although masking was much reduced and both acoustic and electrical waveform distortions were completely lacking. From this unique functional situation, we conclude that the main source of cochlear waveform distortions is a deflection-dependent hair bundle stiffness resulting from constraints imposed by the horizontal top connectors, and not from the intrinsic non-linear behaviour of the mechanoelectrical transducer channel.
PMCID: PMC3338146  PMID: 18849963
2.  Genetic Dissection of the Function of Hindbrain Axonal Commissures 
PLoS Biology  2010;8(3):e1000325.
The Robo3 receptor controls midline crossing by axons. Deleting Robo3 in specific commissural neurons with a conditional knockout reveals their contribution to sensory and motor integration, and models human neurological conditions.
In Bilateria, many axons cross the midline of the central nervous system, forming well-defined commissures. Whereas in mammals the functions of commissures in the forebrain and in the visual system are well established, functions at other axial levels are less clearly understood. Here, we have dissected the function of several hindbrain commissures using genetic methods. By taking advantage of multiple Cre transgenic lines, we have induced site-specific deletions of the Robo3 receptor. These lines developed with the disruption of specific commissures in the sensory, motor, and sensorimotor systems, resulting in severe and permanent functional deficits. We show that mice with severely reduced commissures in rhombomeres 5 and 3 have abnormal lateral eye movements and auditory brainstem responses, respectively, whereas mice with a primarily uncrossed climbing fiber/Purkinje cell projection are strongly ataxic. Surprisingly, although rerouted axons remain ipsilateral, they still project to their appropriate neuronal targets. Moreover, some Cre;Robo3 lines represent potential models that can be used to study human syndromes, including horizontal gaze palsy with progressive scoliosis (HGPPS). To our knowledge, this study is one of the first to link defects in commissural axon guidance with specific cellular and behavioral phenotypes.
Author Summary
Coordination of the left and right sides of the body requires the action of neurons whose axons cross the nervous system midline. The precise contributions of “commissural” neurons to sensory and motor functions remain poorly understood. To probe these crossing circuits, we took advantage of the recent finding that the Robo3 axon guidance receptor is required for midline crossing by axons at most axial levels. A Robo3 conditional knockout mouse line was generated, allowing Robo3 to be deleted in selective neuronal populations. This led to disruption of specific commissures in the sensory, motor, and sensorimotor systems, and resulted in severe but specific functional deficits. Surprisingly, although rerouted axons do not cross the midline, they still project to their appropriate neuronal targets, suggesting that midline crossing is not required to complete the axonal guidance program of those neurons. Moreover, some of the mouse lines represent good models for human syndromes, including horizontal gaze palsy with progressive scoliosis (HGPPS), which is characterized by deficits in coordinated eye movements. This study links defects in commissural axon guidance with specific and dramatic behavioral phenotypes.
PMCID: PMC2834709  PMID: 20231872
3.  Vezatin, an integral membrane protein of adherens junctions, is required for the sound resilience of cochlear hair cells 
EMBO Molecular Medicine  2009;1(2):125-138.
Loud sound exposure is a significant cause of hearing loss worldwide. We asked whether a lack of vezatin, an ubiquitous adherens junction protein, could result in noise-induced hearing loss. Conditional mutant mice bearing non-functional vezatin alleles only in the sensory cells of the inner ear (hair cells) indeed exhibited irreversible hearing loss after only one minute exposure to a 105 dB broadband sound. In addition, mutant mice spontaneously underwent late onset progressive hearing loss and vestibular dysfunction related to substantial hair cell death. We establish that vezatin is an integral membrane protein with two adjacent transmembrane domains, and cytoplasmic N- and C-terminal regions. Late recruitment of vezatin at junctions between MDCKII cells indicates that the protein does not play a role in the formation of junctions, but rather participates in their stability. Moreover, we show that vezatin directly interacts with radixin in its actin-binding conformation. Accordingly, we provide evidence that vezatin associates with actin filaments at cell–cell junctions. Our results emphasize the overlooked role of the junctions between hair cells and their supporting cells in the auditory epithelium resilience to sound trauma.
PMCID: PMC3378116  PMID: 20049712
adherens junction; mouse model; noise-induced hearing loss; organ of Corti; vezatin
5.  Patients affected with Fabry disease have an increased incidence of progressive hearing loss and sudden deafness: an investigation of twenty-two hemizygous male patients 
BMC Medical Genetics  2002;3:10.
Fabry disease (FD, OMIM 301500) is an X-linked inborn error of glycosphingolipid metabolism due to the deficient activity of alpha-galactosidase A, a lysosomal enzyme. While the progressive systemic deposition of uncleaved glycosphingolipids throughout the body is known to have protean clinical manifestations, few data are available regarding the cochlear involvement.
We non-invasively investigated cochlear functions in 22 consecutive hemizygous males (age 19–64 years, mean 39) affected with classic FD. Conventional audiometry, tympanometry, ABR audiometry, otoacoustic emissions were performed in all patients, together with medical history record and physical examination as part of an exhaustive baseline evaluation prior to enzyme replacement therapy.
A total of 12 patients (54.5%) with classic FD were found to have abnormal audition. Five patients had progressive hearing loss and seven patients (32%) experienced sudden deafness. In addition, a hearing loss on high-tone frequencies was found in 7 out of the 10 remaining patients without clinical impairment, despite their young age at time of examination. The incidence of hearing loss appeared significantly increased in FD patients with kidney failure (P < 0.01) or cerebrovascular lesions (P < 0.01), whereas there was no correlation with left ventricular hypertrophy. In addition, tinnitus aurium was also found in six patients (27%).
This is the first evidence of a high incidence of both progressive hearing loss and sudden deafness in a cohort of male patients affected with classic Fabry disease. The exact pathophysiologic mechanism(s) of the cochlear involvement deserves further studies.
PMCID: PMC134464  PMID: 12377100

Results 1-5 (5)