Role of the periotic mesenchyme in the development of sensory cells in early mouse cochlea

Objective:To investigate the role of the periotic mesenchyme(POM)in the development of sensory cells of developing auditory epithelium.Methods:Developing auditory epithelium with or without periotic mesenchyme was isolated from mice at embryonic days 11.5(E11.5),E12.5 and E13.5,respectively,and cultured in vitro to an equivalent of E18.5’s epithelium in vivo.Then,the explants were co-stained with antibodies targeting myosin VIIA,Sox2 and BrdU.Results:More hair cells in E11.5 t 7 DIV,E12.5 t 6 DIV and E13.5 t 5 DIV auditory epithelia were found upon culture with POM(225.90±62.44,476.94±100.81,and 1386.60±202.38,respectively)compared with the non-POM group(68.17±23.74,205.00±44.23,and 1266.80±38.84,respectively).Moreover,regardless of developmental stage,the mesenchymal tissue increased the amount of cochlear sensory cells as well as the ratio of differentiated hair cells to total sensory cells.Conclusions:The periotic mesenchyme promotes the development of cochlear sensory cells,and its effect depends on the developmental stage of the auditory epithelium.

Unidirectional and stage-dependent roles of Notch1 in Wnt-responsive Lgr5+ cells during mouse inner ear development

Wnt and Notch signaling play crucial roles in the determination of the prosensory domain and in the differentiation of hair cells(HCs)and supporting cells during mouse inner ear development;however,the relationship between the two signaling pathways in the mouse cochlea remains largely unknown.Here,we investigated the interactions between Notch and Wnt signaling on the basis of the bidirectional regulation of Notch1 specifically in Wnt-responsive Lgr5+progenitors during different cochlear development stages.We found that the downregulation of Notch1 in Lgr5+cells from embryonic day(E)14.5 to E18.5 can drive the quiescent Lgr5+cells to re-enter the cell cycle and differentiate into extra HCs,whereas the upregulation of Notch1 expression did not affect the proliferation or differentiation of otic progenitor cells.No effect was observed on the upregulation or downregulation of Notch1 in Lgr5+cells from E10.5 to E14.5.We concluded that the roles of Notch1 in Wnt-responsive Lgr5+cells are unidirectional and stage dependent and Notch1 serves as a negative regulator for Lgr5+progenitor activation during cochlear differentiation.Our findings improved the understanding of the interactions between Notch and Wnt signaling in cochlear development.

Bone morphogenetic proteins and inner ear development

Bone morphogenetic proteins(BMPs)are the largest subfamily of the transforming growth factor-βsuperfamily,and they play important roles in the development of numerous organs,including the inner ear.The inner ear is a relatively small organ but has a highly complex structure and is involved in both hearing and balance.Here,we discuss BMPs and BMP signaling pathways and then focus on the role of BMP signal pathway regulation in the development of the inner ear and the implications this has for the treatment of human hearing loss and balance dysfunction.

Spatiotemporal expression of Ezh2 in the developing mouse cochlear sensory epithelium

The enhancer of zeste 2 polycomb repressive complex 2 subunit （Ezh2） is a histone-lysine N- methyltransferase enzyme that participates in DNA methylation. Ezh2 has also been reported to play crucial roles in stem cell proliferation and differentiation. However, the detailed expression profile of Ezh2 during mouse cochlear development has not been investigated. Here, we examined the spatiotemporal expression of Ezh2 in the cochlea during embryonic and postnatal development. Ezh2 expression began to be observed in the whole otocyst nuclei at embryonic day 9.5 （E9.5）. At E12.5, Ezh2 was expressed in the nuclei of the cochlear prosensory epithelium. At E13.5 and E15.5, Ezh2 was expressed from the apical to the basal turns in the nuclei of the differentiating cochlear epithelium. At postnatal day （P） 0 and 7, the Ezh2 expression was located in the nuclei of the cochlear epithelium in all three turns and could be clearly seen in outer and inner hair cells, supporting cells, the stria vascularis, and spiral ganglion cells. Ezh2 continued to be expressed in the cochlear epithelium of adult mice. Our results provide the basic Ezh2 expression pattern and might be useful for further investigating the detailed role of Ezh2 during cochlear development.