ZBTB20 is Essential for Cochlear Maturation and Hearing in Mice

Abstract

The mammalian cochlear epithelium undergoes substantial remodeling and maturation before the onset of hearing. However, very little is known about the transcriptional network governing cochlear late-stage maturation and particularly the differentiation of its lateral non-sensory region. Here we establish ZBTB20 as an essential transcription factor required for cochlear terminal differentiation and maturation and hearing. ZBTB20 is abundantly expressed in the developing and mature cochlear non-sensory epithelial cells, with transient expression in immature hair cells and spiral ganglion neurons. Otocyst-specific deletion of Zbtb20 causes profound deafness with reduced endolymph potential in mice. The subtypes of cochlear epithelial cells are normally generated but their postnatal development is arrested in the absence of ZBTB20, as manifested by an immature appearance of the organ of Corti, malformation of tectorial membrane, a flattened spiral prominence, and a lack of identifiable Boettcher cells. Furthermore, these defects are related with a failure in the terminal differentiation of the non-sensory epithelium covering the outer border Claudius cells, outer sulcus root cells and spiral prominence epithelial cells. Transcriptome analysis shows ZBTB20 regulates genes coding for tectorial membrane proteins in the greater epithelial ridge, and those preferentially expressed in root cells and spiral prominence epithelium. Our results point to ZBTB20 as an essential regulator for postnatal cochlear maturation and particularly for the terminal differentiation of cochlear lateral non-sensory domain.

Targeted Deletion of All Known Thyroid Hormone Receptors Causes Maturation Retardation and Early-onset Degeneration of Cochlear Outer Sulcus

“…Several lines of evidence including our recently published report suggests that root cells may play important roles in the maintenance of endolymph homeostasis and EP (9,12,10,20). Our findings in this study also support this hypothesis and imply that root cell dysfunction may at least partially contribute to a reduced EP upon deficiency of TH or all known TRs during the critical period of cochlear development (4,6,36).…”

“…We and others have previously shown that root cell cytoplasm and their processes are enriched with acetyl-α-tubulin (13,20,28). To better visualize root cells, we then performed immunofluorescence staining for acetyl-α-tubulin.…”

“…During this developmental window, cochlear sensory epithelium undergoes dramatic morphological changes including regression of GER leading to the formation of inner sulcus, and opening of the tunnel of Corti (14,52). Concomitantly, the outer sulcus epithelium transformes from a simple layer of cuboidal-shaped cells lining the scala media into root cells with large, branched processes resided deep in the spiral ligament (18,20,52). This study uncovers that TH or TRs is nessesary for the outer sulcus remodeling, in addition to previous reported GER regression and the organ of Corti maturation (6) Another intrigueing finding of this study is the early-onset progressive degeneration of root cells observed only in OV-TRα/βKO but not OV-TRβKO cochlea, suggesting TRα and TRβ play a combined role in root cell survival.…”

“…Immunostaining was performed essentially as previously described (20). X-gal staining was done as previously published (67).…”

“…ABRs were recorded using a TDT RZ6/BioSigRZ system (Tucker-Davis Tech. Inc., US) as previously described (20). Briefly, anesthetized mice were kept on a heated mat in a soundproof chamber.…”