Hartman Byron H, Basak Onur, Nelson Branden R, Taylor Verdon, Bermingham-McDonogh Olivia, Reh Thomas A
Department of Biological Structure, University of Washington, Seattle, WA 98195, USA.
J Assoc Res Otolaryngol. 2009 Sep;10(3):321-40. doi: 10.1007/s10162-009-0162-2. Epub 2009 Apr 17.
The Notch signaling pathway is known to have multiple roles during development of the inner ear. Notch signaling activates transcription of Hes5, a homologue of Drosophila hairy and enhancer of split, which encodes a basic helix-loop-helix transcriptional repressor. Previous studies have shown that Hes5 is expressed in the cochlea during embryonic development, and loss of Hes5 leads to overproduction of auditory and vestibular hair cells. However, due to technical limitations and inconsistency between previous reports, the precise spatial and temporal pattern of Hes5 expression in the postnatal and adult inner ear has remained unclear. In this study, we use Hes5-GFP transgenic mice and in situ hybridization to report the expression pattern of Hes5 in the inner ear. We find that Hes5 is expressed in the developing auditory epithelium of the cochlea beginning at embryonic day 14.5 (E14.5), becomes restricted to a particular subset of cochlear supporting cells, is downregulated in the postnatal cochlea, and is not present in adults. In the vestibular system, we detect Hes5 in developing supporting cells as early as E12.5 and find that Hes5 expression is maintained in some adult vestibular supporting cells. In order to determine the effect of hair cell damage on Notch signaling in the cochlea, we damaged cochlear hair cells of adult Hes5-GFP mice in vivo using injection of kanamycin and furosemide. Although outer hair cells were killed in treated animals and supporting cells were still present after damage, supporting cells did not upregulate Hes5-GFP in the damaged cochlea. Therefore, absence of Notch-Hes5 signaling in the normal and damaged adult cochlea is correlated with lack of regeneration potential, while its presence in the neonatal cochlea and adult vestibular epithelia is associated with greater capacity for plasticity or regeneration in these tissues; which suggests that this pathway may be involved in regulating regenerative potential.
已知Notch信号通路在内耳发育过程中具有多种作用。Notch信号激活Hes5的转录，Hes5是果蝇毛状基因和分裂增强子的同源物，编码一种碱性螺旋-环-螺旋转录抑制因子。先前的研究表明，Hes5在胚胎发育期间在耳蜗中表达，Hes5的缺失会导致听觉和前庭毛细胞过度产生。然而，由于技术限制以及先前报告之间的不一致，Hes5在出生后和成年内耳中的精确时空表达模式仍不清楚。在本研究中，我们使用Hes5-GFP转基因小鼠和原位杂交技术来报告Hes5在内耳中的表达模式。我们发现，Hes5从胚胎第14.5天（E14.5）开始在耳蜗发育中的听觉上皮中表达，随后局限于耳蜗支持细胞的特定亚群，在出生后的耳蜗中表达下调，在成年动物中不存在。在前庭系统中，我们最早在E12.5时就在发育中的支持细胞中检测到Hes5，并发现Hes5在一些成年前庭支持细胞中持续表达。为了确定毛细胞损伤对耳蜗中Notch信号的影响，我们通过注射卡那霉素和速尿在体内损伤成年Hes5-GFP小鼠的耳蜗毛细胞。尽管在处理后的动物中外毛细胞被杀死，损伤后支持细胞仍然存在，但在受损的耳蜗中支持细胞并未上调Hes5-GFP的表达。因此，正常和受损成年耳蜗中Notch-Hes5信号的缺失与再生潜能的缺乏相关，而其在新生耳蜗和成年前庭上皮中的存在与这些组织中更大的可塑性或再生能力相关；这表明该信号通路可能参与调节再生潜能。
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