Atoh1 expression and function during auditory hair cell regeneration in post-hatch chickens

• Published in: Hearing research 2012-07, Vol.289 (1-2), p.74-85
• Main Authors: Lewis, Rebecca M., Hume, Clifford R., Stone, Jennifer S.
• Format: Article
• Language: English
• Subjects: Amyloid Precursor Protein Secretases - antagonists & inhibitors; Amyloid Precursor Protein Secretases - metabolism; Animals; Auditory system; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; Cell Cycle; Cell Transdifferentiation; Chickens; Differentiation; Dipeptides - pharmacology; Electroporation; Enhancer Elements, Genetic; Enhancers; Enzyme Inhibitors - pharmacology; Epithelium; Gene Expression Regulation; Gene Transfer Techniques; Genes, Reporter; Hair cells; Hair Cells, Auditory - drug effects; Hair Cells, Auditory - metabolism; Hair Cells, Auditory - pathology; Hearing; Helix-loop-helix proteins; Labyrinth Supporting Cells - drug effects; Labyrinth Supporting Cells - metabolism; Labyrinth Supporting Cells - pathology; Notch protein; Organ Culture Techniques; Receptors, Notch - metabolism; Regeneration - drug effects; RNA, Messenger - metabolism; Secretase; Signal transduction; Streptomycin - toxicity; Time Factors; Transcription factors; Transcriptional Activation
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2012.04.008

Loss of hair cells in humans leads to irreversible hearing deficits, since auditory hair cells are not replaced. In contrast, hair cells are regenerated in the auditory epithelium of mature birds after damage by non-sensory supporting cells that transdifferentiate into hair cells by mitotic and/or non-mitotic mechanisms. Factors controlling these processes are poorly understood. The basic helix-loop-helix transcription factor ATOH1 is both necessary and sufficient for developmental hair cell differentiation, but it is unclear if it plays the same role in the mitotic and non-mitotic pathways in hair cell regeneration. We examined Atoh1 expression and function during hair cell regeneration in chickens. Atoh1 transcripts were increased in many supporting cells in the damaged auditory epithelium shortly after ototoxin administration and later became restricted to differentiating hair cells. Fate-mapping in vitro using an Atoh1 enhancer reporter demonstrated that only 56% of the supporting cells that spontaneously upregulate Atoh1 enhancer activity after damage acquired the hair cell fate. Inhibition of notch signaling using a gamma secretase antagonist stimulated an increase in Atoh1 reporter activity and induced a higher proportion of supporting cells with Atoh1 activity (73%) to differentiate as hair cells. Forced overexpression of Atoh1 in supporting cells triggered 66% of them to acquire the hair cell fate and nearly tripled their likelihood of cell cycle entry. These findings demonstrate that Atoh1 is broadly upregulated in supporting cells after damage, but a substantial proportion of supporting cells with Atoh1 activation fails to acquire hair cell features, in part due to gamma secretase-dependent activities. ► Only half of supporting cells that activate Atoh1 become hair cells. ► Notch inactivation increases this rate to 73%. ► Atoh1 overexpression induces 66% of supporting cells to become hair cells. ► Atoh1 overexpression induces nearly 3× the supporting cells to divide. ► Future studies should investigate factors beside notch blocking transdifferentiation.