Abstract
A study of genes expressed in the developing inner ear identified the bHLH transcription factor Scleraxis (Scx) in the developing cochlea. Previous work has demonstrated an essential role for Scx in the differentiation and development of tendons, ligaments and cells of chondrogenic lineage. Expression in the cochlea has been shown previously, however the functional role for Scx in the cochlea is unknown. Using a Scx-GFP reporter mouse line we examined the spatial and temporal patterns of Scx expression in the developing cochlea between embryonic day 13.5 and postnatal day 25. Embryonically, Scx is expressed broadly throughout the cochlear duct and surrounding mesenchyme and at postnatal ages becomes restricted to the inner hair cells and the interdental cells of the spiral limbus. Deletion of Scx results in hearing impairment indicated by elevated auditory brainstem response (ABR) thresholds and diminished distortion product otoacoustic emission (DPOAE) amplitudes, across a range of frequencies. No changes in either gross cochlear morphology or expression of the Scx target genes Col2A, Bmp4 or Sox9 were observed in Scx − /− mutants, suggesting that the auditory defects observed in these animals may be a result of unidentified Scx-dependent processes within the cochlea.
Highlights
The organ of Corti is a neuro-sensory epithelium within the mammalian cochlea that contains the sensory hair cells required for mechanotransduction
No changes in either gross cochlear morphology or expression of the Scx target genes Col2A, Bmp4 or Sry-type HMG box 9 (Sox9) were observed in Scx2/2 mutants, suggesting that the auditory defects observed in these animals may be a result of unidentified Scx-dependent processes within the cochlea
Hair cells are precisely patterned during development into a characteristic arrangement of a single row of inner hair cells (IHCs) and three rows of outer hair cells (OHCs)
Summary
The organ of Corti is a neuro-sensory epithelium within the mammalian cochlea that contains the sensory hair cells required for mechanotransduction. Sox9 is dynamically expressed in the mesenchymal cells of the developing inner ear where it regulates the differentiation and expansion of otic fibrocytes, the formation of the otic capsule and coiling of the cochlear duct [20].
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