The heterogeneity of mammalian utricular cells over the course of development

Abstract

Background The inner ear organ is a delicate tissue consisting of hair cells (HCs) and supporting cells (SCs).The mammalian inner ear HCs are terminally differentiated cells that cannot spontaneously regenerate in adults. Epithelial non‐hair cells (ENHCs) in the utricle include HC progenitors and SCs, and the progenitors share similar characteristics with SCs in the neonatal inner ear. Methods We applied single‐cell sequencing to whole mouse utricles from the neonatal period to adulthood, including samples from postnatal day (P)2, P7 and P30 mice. Furthermore, using transgenic mice and immunostaining, we traced the source of new HC generation. Results We identified several sensory epithelial cell clusters and further found that new HCs arose mainly through differentiation from Sox9+ progenitor cells and that only a few cells were produced by mitotic proliferation in both neonatal and adult mouse utricles. In addition, we identified the proliferative cells using the marker UbcH10 and demonstrated that in adulthood the mitotically generated HCs were primarily found in the extrastriola. Moreover, we observed that not only Type II, but also Type I HCs could be regenerated by either mitotic cell proliferation or progenitor cell differentiation. Conclusions Overall, our findings expand our understanding of ENHC cell fate and the characteristics of the vestibular organs in mammals over the course of development.

Cross‐species analysis and comparison of the inner ear between chickens and mice

“…In the sensory epithelium of inner ear, Myo7a (Jones & Warchol, 2009) and Parvalbumin (You et al., 2022) label HCs, and Sox2 (Morgan et al., 2016) (You et al., 2022) labels supporting cells. We double‐labeled Myo7a and Sox2 along the entire length of the chicken cochlear duct through the transverse section.…”

“…The primary antibodies and secondary fluorescent antibodies used in this study are listed in Table 1. The primary antibodies have been characterized well in previous studies (Jiang et al., 2022; Jones & Warchol, 2009; Kawai et al., 2021; Morgan et al., 2016; You et al., 2022). Nuclei were labeled with DAPI (1:800 dilution, Sigma‐Aldrich, D9542) for 10 min at room temperature.…”

“…In the sensory epithelium of inner ear, Myo7a (Jones & Warchol, 2009) and Parvalbumin (You et al, 2022) We double-labeled Myo7a and Sox2 along the entire length of the chicken cochlear duct through the transverse section. We made cross-sections of frozen samples of the cochlear duct, which is proximal to the lagena, and found that certain areas were devoid of Myo7a/Sox2 double-positive cells (Figure 3a,b).…”

Future Pharmacotherapy for Sensorineural Hearing Loss by Protection and Regeneration of Auditory Hair Cells

“…In contrast to mammalian cochleae, mammalian vestibular sensory organs retain the capacity for HC regeneration. Recent publications of mouse utricles demonstrated gene expression profiles during HC regeneration at a single-cell level [ 98 , 99 ]. Based on these data, practical strategies for inducing HC regeneration will be developed for mature mammalian cochleae.…”

Revealing heterogeneity and damage response in the adult human utricle

“…In embryonic and newborn mouse utricles, SCs can regenerate HCs by proliferation or direct SC-to-HC transdifferentiation during homeostasis and after ototoxic damage 6,7,8 , and this ability drastically declines with age 6,9 . Singlecell RNA-sequencing (scRNA-seq) of the mouse utricle has improved our understanding of utricle biology during development 10,11,12 , at maturity 13 , and after damage 14,15 . However, information on the human utricle is still scarce.…”