The Helios Transcription Factor is Necessary for Both Outer Hair Cell Development and Maintenance

Authors

• N Ibrahim
• E Lee

Abstract

In 2018, our laboratories demonstrated that the transcription factor helios is essential for OHC maturation. We showed that a mutation in the Ikzf2 gene, which encodes helios, resulted in a reduction in prestin-dependent electromotility and early-onset hearing loss. Moreover, ectopic expression of helios in inner hair cells (IHCs) led to the downregulation of markers specific to IHCs and a transcriptional shift towards an OHC-like state. In this study, we tested whether helios also plays a role in maintaining OHC function after the onset of hearing. Ikzf2 was conditionally deleted by crossing Ikzf2 floxed mice with either Gfi1-Cre (depletion beginning at ~E16.5) or Prestin-CreERT2 (tamoxifen-induced at P12/13/14) mice. Auditory function of these Ikzf2 cKO mice was evaluated at 6-weeks of age by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) measurements. To evaluate OHC loss, cytocochleaograms were performed on whole mount cochlear preparations from 6-week-old mice, stained with phalloidin, DAPI and an anti-prestin antibody. To define the regulatory transcriptional cascade downstream of helios, OHCs from P8 Ikzf2fl/fl;Gfi1Cre mice and their littermate controls were isolated by flow cytometry, and analyzed by bulk and scRNA-seq. Both mouse lines with conditionally deleted Ikzf2 exhibited elevated ABR hearing thresholds and increased DPOAE thresholds across all frequencies tested. Aberrant OHC morphology and OHC loss is observed in both mouse models, with the fewest OHCs remaining in the Ikzf2fl/fl;Gfi1Cre mice. Lastly, transcriptional changes were recorded in the helios-deficient OHCs. Our data reveal that in addition to OHC development helios is also critical for their maintenance.

Scientific Focus Area: Genetics and Genomics

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