Gipc3 mutations associated with audiogenic seizures and sensorineural hearing loss in mouse and human

Sensorineural hearing loss affects the quality of life and communication of millions of people, but the underlying molecular mechanisms remain elusive. Here, we identify mutations in Gipc3 underlying progressive sensorineural hearing loss (age-related hearing loss 5, ahl5) and audiogenic seizures (juvenile audiogenic monogenic seizure 1, jams1) in mice and autosomal recessive deafness DFNB15 and DFNB95 in humans. Gipc3 localizes to inner ear sensory hair cells and spiral ganglion. A missense mutation in the PDZ domain has an attenuating effect on mechanotransduction and the acquisition of mature inner hair cell potassium currents. Magnitude and temporal progression of wave I amplitude of afferent neurons correlate with susceptibility and resistance to audiogenic seizures. The Gipc3343A allele disrupts the structure of the stereocilia bundle and affects long-term function of auditory hair cells and spiral ganglion neurons. Our study suggests a pivotal role of Gipc3 in acoustic signal acquisition and propagation in cochlear hair cells

Structure and Function of the Hair Cell Ribbon Synapse

Faithful information transfer at the hair cell afferent synapse requires synaptic transmission to be both reliable and temporally precise. The release of neurotransmitter must exhibit both rapid on and off kinetics to accurately follow acoustic stimuli with a periodicity of 1 ms or less. To ensure such remarkable temporal fidelity, the cochlear hair cell afferent synapse undoubtedly relies on unique cellular and molecular specializations. While the electron microscopy hallmark of the hair cell afferent synapse — the electron-dense synaptic ribbon or synaptic body — has been recognized for decades, dissection of the synapse’s molecular make-up has only just begun. Recent cell physiology studies have added important insights into the synaptic mechanisms underlying fidelity and reliability of sound coding. The presence of the synaptic ribbon links afferent synapses of cochlear and vestibular hair cells to photoreceptors and bipolar neurons of the retina. This review focuses on major advances in understanding the hair cell afferent synapse molecular anatomy and function that have been achieved during the past years

The pattern of sensorineural degeneration in the cochlea of the deaf shaker-1 mouse: ultrastructural observations.

Experiments were done to extend existing knowledge on the nature and course of postnatal sensory and neural changes in the inner ear of shaker-1 mutant mice. Mice, 3-, 6-, 10-, 12-, 18-, and 30 days old, homozygous for the sh-1 gene, were studied using transmission electron microscopy. The data indicate retarded development coupled with the early onset of progressive degeneration in Corti's organ, its nerve supply, and the cells of the spiral ganglion. Especially noteworthy are the following: in 3-day-old mice both outer hair cells and spiral ganglion cells are already abnormal. The latter are especially loosely ensheathed by glial cells and are in direct contact with nerve fibers. Outer hair cells contain vacuoles and lysosomes. By 6 days of age inner hair cells come to be similarly affected. By 18 days most of the afferent nerve supply of the organ of Corti has degenerated. The behavior of efferents within the organ is complex. Efferents arrive late (day 12) at the outer hair cells, they are few in number, form only immature synapses with the cell, and they subsequently degenerate. In contrast, the efferent nerve supply of the inner hair cell appears normal, if not over-abundant. The simultaneous occurrence of organ of Corti and spiral ganglion cell anomalies is discussed in terms of the role of sensorineural interactions in the expression of genetic defects affecting the inner ear. The selective degeneration of efferents to outer hair cells is viewed as being consistent with the hypothesis that there are two independent efferent systems which innervate the two types of cochlear sensory hair cells