Abstract
A cardinal feature of the auditory pathway is frequency selectivity, represented in 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 the molecular and cellular features of auditory neurons, including the formation of the spiral ganglion and peripheral and central processes that shape the tonotopic representation of the auditory map. We selectively knocked outIsl1in auditory neuronsusingNeurod1Crestrategies.
In the absence ofIsl1, spiral ganglion neurons migrate into the central cochlea and beyond, and the cochlear wiring is profoundly reduced and disrupted. The central axons ofIsl1mutants lose their topographic projections and segregation at the cochlear nucleus.
Transcriptome analysis of spiral ganglion neurons showsthatIsl1regulates neurogenesis, axonogenesis, migration, neurotransmission-related machinery, and synaptic communication patterns. We show that peripheral disorganization in the cochlea affects the physiological properties of hearing in the midbrain andauditory behavior.
Surprisingly, auditory processing features are preserved despite thesignificant hearing impairment, revealing central auditory pathway resilience and plastic-ity inIsl1mutant mice. Mutant mice have a reduced acoustic startle reflex, altered pre-pulse inhibition, and characteristics of compensatory neural hyperactivity centrally.
Our findings show that ISL1 is one of the obligatory factors required to sculpt auditory structural and functional tonotopic maps. Still, uponIsl1deletion, the ensuing central plasticity of the auditory pathway does not suffice to overcome developmentally induced peripheral dysfunction of the cochlea.