Uncoordinated maturation of developing and regenerating postnatal mammalian vestibular hair cells

Abstract

Sensory hair cells are mechanoreceptors required for hearing and balance functions. From embryonic development, hair cells acquire apical stereociliary bundles for mechanosensation, basolateral ion channels that shape receptor potential, and synaptic contacts for conveying information centrally. These key maturation steps are sequential and presumed coupled; however, whether hair cells emerging postnatally mature similarly is unknown. Here, we show that in vivo postnatally generated and regenerated hair cells in the utricle, a vestibular organ detecting linear acceleration, acquired some mature somatic features but hair bundles appeared nonfunctional and short. The utricle consists of two hair cell subtypes with distinct morphological, electrophysiological and synaptic features. In both the undamaged and damaged utricle, fate-mapping and electrophysiology experiments showed that Plp1 + supporting cells took on type II hair cell properties based on molecular markers, basolateral conductances and synaptic properties yet stereociliary bundles were absent, or small and nonfunctional. By contrast, Lgr5 + supporting cells regenerated hair cells with type I and II properties, representing a distinct hair cell precursor subtype. Lastly, direct physiological measurements showed that utricular function abolished by damage was partially regained during regeneration. Together, our data reveal a previously unrecognized aberrant maturation program for hair cells generated and regenerated postnatally and may have broad implications for inner ear regenerative therapies.

Atoh1 Directs Regeneration and Functional Recovery of the Mature Mouse Vestibular System

“…In the developing utricle, specified HCs first acquire bundles and mechanotransduction and subsequently basolateral potassium currents and nerve terminals characteristic of HC subtype specialization (Geleoc et al, 2004). Therefore, unlike developing HCs, apical bundles in regenerating HCs fail to mature despite grossly normal synaptic elements and innervation (Atkinson et al, 2015; Zheng and Zuo, 2017; Wang et al, 2019). Such discrepancies in the degrees of maturation of bundles and basolateral features were previously observed in ectopic HCs in the neonatal and mature cochlea and HCs derived from embryonic stem cells (Gubbels et al, 2008; Oshima et al, 2010; Walters et al, 2017).…”

Dynamic patterns of YAP1 expression and cellular localization in the developing and injured utricle

“…Also, the E-cadherin-mediated cellular junctions in the neonatal utricle are not fully mature at P5 50 , so the epithelium may not be able to maintain integrity after a high level of DT-mediated hair cell death. Finally, the dose of DT used in the present study (5 ng/g) was slightly higher than the dose used in prior studies 51 . In any case, we found that these lesions closed spontaneously within seven days, similar to the pattern of closure observed after in vitro puncture wounds in the utricles of embryonic mice 52 .…”

Effects of cochlear hair cell ablation on spatial learning/memory

“…2c). However, the mean utricle hair cell loss of 8.96% was less than the > 60% loss necessary to be physiologically detected 20,21 . Furthermore, when comparing movement metrics between WT and DTR, there was no significant difference in mean movement velocity (one-tailed t-test: 5.766 cm/s [95% CI 5.512, 6.020] vs 5.848 cm/s [95% CI 5.648, 6.048], p = 0.610) and subjective assessment of gait on visual and center-point video tracking analysis revealed no apparent differences between groups.…”

“…There was no difference in RGC counts between WT and DTR animals at 2 and 10 dpi ( Fig. 2f; one-way ANOVA: F [2,21] = 0.09, p = 0.9133). All animals reacted to visual confrontation and demonstrated seeing behavior throughout the experiment.…”

“…Results reported were from 8 hemispheres from 4 animals per condition. There was no difference between WT and DTR animals at 2 and 10 dpi in number of striatal nuclei (one-way ANOVA: F [2,21] = 0.50, p = 0.6154) or neurons (one-way ANOVA: F [2, 21] = 1.47, p = 0.2522; Fig. 2j).…”