Three distinctAtoh1enhancers cooperate for sound receptor hair cell development

Abstract

Cochlear hair cells (HCs) in the inner ear are responsible for sound detection. For HC fate specification, the master transcription factor Atoh1 is both necessary and sufficient. Atoh1 expression is dynamic and tightly regulated during development, but the cis -regulatory elements mediating this regulation remain unresolved. Unexpectedly, we found that deleting the only recognized Atoh1 enhancer, defined here as Eh1, failed to impair HC development. By using the assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), we discovered two additional Atoh1 enhancers: Eh2 and Eh3. Notably, Eh2 deletion was sufficient for impairing HC development, and concurrent deletion of Eh1 and Eh2 or all three enhancers resulted in nearly complete absence of HCs. Lastly, we showed that Atoh1 binds to all three enhancers, consistent with its autoregulatory function. Our findings reveal that the cooperative action of three distinct enhancers underpins effective Atoh1 regulation during HC development, indicating potential therapeutic approaches for HC regeneration.

Defective mechanosensory transduction of the new inner hair cells prevents hearing recover in the damaged cochlea

“…Notably, both OHCs and IHCs are critical for sound detection and their damage causes permanent deafness in mammals, which have lost HC regeneration capacity (11–13). Intriguingly, the b-HLH transcription factor Atoh1 is necessary for cochlear pan-HC development: whereas all HCs disappear in Atoh1 -/- mice (14–16), Atoh1 overexpression induces supernumerary new HCs (17–21). Furthermore, Insm1 and Ikzf2 play crucial roles in specifying or stabilizing the OHC fate (22, 23), and our group and two other groups have independently shown that Tbx2 is required in IHC fate specification, differentiation, and maintenance (24–26).…”

Deciphering the genetic interactions between Pou4f3, Gfi1, and Rbm24 in maintaining cochlear hair cell survival

“…Whether Eh1, Eh2, and Eh3 are bona-fide Rbm24 enhancers has remained unknown. We reasoned that if Eh1, Eh2, and Eh3 were Rbm24 enhancers, one of these, together with the mini-promoter of mouse heat shock protein 68 gene (Hsp68) [8,[45][46][47], would be sufficient…”

“…Two types of HCs exist, the inner HCs (IHCs) and outer HCs (OHCs), and these appear in, respectively, a single row and three rows [3]. Both OHCs and IHCs are derived from cochlear progenitors expressing high levels of ATOH1, a master transcription factor (TF) in HC development [4][5][6], and no HCs form in the Atoh1 -/cochlea, highlighting the essential role of ATOH1 in specifying the general HC fate in the undifferentiated progenitors [7,8].…”

“…Two types of HCs exist, the inner HCs (IHCs) and outer HCs (OHCs), and these appear in, respectively, a single row and three rows [3]. Both OHCs and IHCs are derived from cochlear progenitors expressing high levels of ATOH1, a master transcription factor (TF) in HC development [4][5][6], and no HCs form in the Atoh1 -/cochlea, highlighting the essential role of ATOH1 in specifying the general HC fate in the undifferentiated progenitors [7,8]. Whereas OHCs uniquely express the motor protein PRESTIN (encoded by Slc26a5) and function as sound amplifiers [9,10], IHCs specifically express FGF8, vGLUT3 (encoded by Slc17a8), and OTOFERLIN [11][12][13][14][15] and act as the primary sensory cells that form synapses with distinct subtypes of type I spiral (auditory) neurons [16][17][18][19].…”

Revisiting the potency of Tbx2 expression in transforming outer hair cells into inner hair cells at multiple agesin vivo

“…Both IHCs and OHCs are descendants of Atoh1+ cochlear prosensory progenitors 9,10 . Atoh1 is a master TF essential for cochlear HC production 11,12 . Nevertheless, Atoh1 should not be directly involved in the bifurcation of the progenitors into IHCs or OHCs, because both IHC and OHC development are severely defective in Atoh1 -/- mice 13–17 .…”