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ISL1 is an essential determinant of structural and functional tonotopic representation of sound

ABSTRACT: A cardinal feature of the auditory pathway is frequency selectivity represented in the form of a tonotopic map from the cochlea to the cortex. The molecular determinants of the auditory frequency map are unknown. Here, we discovered that the transcription factor ISL1 regulates features of auditory neurons, including the formation of the spiral ganglion neuron (SGN) and peripheral and central processes that shape the tonotopic representation of the auditory map. We selectively knocked out Isl1 in auditory neurons using Neurod1Cre strategies. In the absence of Isl1, SGNs migrate into the central cochlea and beyond. The cochlear wiring is profoundly reduced and disrupted. The central axons of Isl1 mutants lose their topographic projections and segregation at the cochlear nucleus. Transcriptome analysis of SGNs shows that Isl1 regulates neurogenesis, axonogenesis, migration, and the functional properties of neurons. Surprisingly, notable auditory processing features are preserved despite the significant hearing impairment, revealing central auditory pathway resilience and plasticity in mutant mice. Mutant mice demonstrate altered acoustic startle reflex, prepulse inhibition, characteristics of compensatory neural hyperactivity centrally. Our findings show that the Isl1 is one of the obligatory factors required to sculpt auditory structural and functional tonotopic maps. Still, upon Isl1 deletion, the ensuing compensatory plasticity of the auditory pathway does not suffice to overcome developmental changes at the peripheral sensory organ.

ORGANISM(S): Mus musculus

PROVIDER: GSE182575 | GEO | 2022/09/01

REPOSITORIES: GEO

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Project description:Spiral ganglion neurons (SGNs) and the associated components of the auditory nerve are primary carriers of auditory information from hair cells to the brain. Loss of SGNs occurs with many pathological conditions, resulting in permanent sensorineural hearing loss. Neural stem/progenitors (NSPs) have been well-characterized in several locations of adult brain and retina. However, it is unclear whether NSPs are present in the adult auditory nerve. Here we examined the self-renewal potential of the adult auditory nerve using ouabain application as a well-established mouse model of acute SGN injury. The observed increase in cell proliferation, alteration in enchromatin/heterochromatin ratio and down-regulation of histone deacetylase expression in glial cells suggest that the quiescent glial cells convert to an activated state after SGN degeneration. This was further confirmed by global gene expression analysis of injured auditory nerves, which showed up-regulation of numerous neurogenesis- and/or development-associated genes shortly after ouabain exposure. These genes include molecular markers commonly used for the identification of NSPs. Under a strict culture regimen, auditory nerve-derived cells of adult mouse ears gave rise to neurospheres, suggesting that multipotent NSPs are present in adult cochlear nerve. Neurosphere assays on Sox2 transgenic mice revealed that Sox2+ glial cells are the source for NSPs. Our data also showed that acute injury or hypoxia enhances neurosphere formation. Taken together, our study revealed that glial cells of adult cochlea exhibit several NSP characteristics, and hence these mature non-neuronal cells may be important targets for promoting self-repair of degenerative auditory nerves. Analysis was conducted on auditory nerve samples from stages encompassing maturation and onset of hearing. Cochleas were collected from euthanized mice (CBA/CaJ) at perinatal (P) stages P0, P3, P7, P10, P14 and P21. Cochleas underwent microdissection to remove the outer bony cochlear shell and cochlear lateral wall, thus preserving the modiolus portion of cochlea which contains mainly the auditory nerve. Paired cochleas (i.e., from left and right ears) from each mouse were pooled to make individual samples. All sample types were done in experimental duplicate (n=2).

Project description:Spiral ganglion neurons (SGNs) and the associated components of the auditory nerve are primary carriers of auditory information from hair cells to the brain. Loss of SGNs occurs with many pathological conditions, resulting in permanent sensorineural hearing loss. Neural stem/progenitors (NSPs) have been well-characterized in several locations of adult brain and retina. However, it is unclear whether NSPs are present in the adult auditory nerve. Here we examined the self-renewal potential of the adult auditory nerve using ouabain application as a well-established mouse model of acute SGN injury. The observed increase in cell proliferation, alteration in enchromatin/heterochromatin ratio and down-regulation of histone deacetylase expression in glial cells suggest that the quiescent glial cells convert to an activated state after SGN degeneration. This was further confirmed by global gene expression analysis of injured auditory nerves, which showed up-regulation of numerous neurogenesis- and/or development-associated genes shortly after ouabain exposure. These genes include molecular markers commonly used for the identification of NSPs. Under a strict culture regimen, auditory nerve-derived cells of adult mouse ears gave rise to neurospheres, suggesting that multipotent NSPs are present in adult cochlear nerve. Neurosphere assays on Sox2 transgenic mice revealed that Sox2+ glial cells are the source for NSPs. Our data also showed that acute injury or hypoxia enhances neurosphere formation. Taken together, our study revealed that glial cells of adult cochlea exhibit several NSP characteristics, and hence these mature non-neuronal cells may be important targets for promoting self-repair of degenerative auditory nerves. Adult Mice (CBA/CaJ, aged 8 to 12 weeks) were anesthetized and subjected to survival surgery to expose the bulla of the right ear. A ouabain solution (3 mM, approximately 10 ul) was administered in the round window niche. This solution was wicked away and replaced with fresh ouabain approximately every 10 min during a cummulative exposure period of 60 min. The left ears (i.e., contralateral) were not surgically manipulated and were used as controls. Mice were maintained for 3 days or 7 days following treatments, then euthanized, and the oubain-treated and contralateral cochleas were removed. Cochleas underwent microdissection to remove the outer bony cochlear shell and cochlear lateral wall, thus preserving the modiolus portion of cochlea which contains mainly the auditory nerve. All sample types were prepared in experimental triplicate (n=3).

Project description:Spiral ganglion neurons (SGNs) and the associated components of the auditory nerve are primary carriers of auditory information from hair cells to the brain. Loss of SGNs occurs with many pathological conditions, resulting in permanent sensorineural hearing loss. Neural stem/progenitors (NSPs) have been well-characterized in several locations of adult brain and retina. However, it is unclear whether NSPs are present in the adult auditory nerve. Here we examined the self-renewal potential of the adult auditory nerve using ouabain application as a well-established mouse model of acute SGN injury. The observed increase in cell proliferation, alteration in enchromatin/heterochromatin ratio and down-regulation of histone deacetylase expression in glial cells suggest that the quiescent glial cells convert to an activated state after SGN degeneration. This was further confirmed by global gene expression analysis of injured auditory nerves, which showed up-regulation of numerous neurogenesis- and/or development-associated genes shortly after ouabain exposure. These genes include molecular markers commonly used for the identification of NSPs. Under a strict culture regimen, auditory nerve-derived cells of adult mouse ears gave rise to neurospheres, suggesting that multipotent NSPs are present in adult cochlear nerve. Neurosphere assays on Sox2 transgenic mice revealed that Sox2+ glial cells are the source for NSPs. Our data also showed that acute injury or hypoxia enhances neurosphere formation. Taken together, our study revealed that glial cells of adult cochlea exhibit several NSP characteristics, and hence these mature non-neuronal cells may be important targets for promoting self-repair of degenerative auditory nerves. Auditory nerves were removed from the temporal bones of adult CBA/CaJ mice, aged 8 to 12 weeks. Tissues were either collected and used directly as the tissue samples or dissociated and used for the cell culture samples. Dissociated auditory nerve cells were propagated and grown to full confluency (5-7 days), constituting the cultured cell samples. For neurosphere samples, growth medium was changed to neurosphere formation medium and the cells were cultured for an additional 12 days. All samples were prepared in triplicate (n=3).

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ISL1 is an essential determinant of structural and functional tonotopic representation of sound

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