Cafaro Jon, Lee Gi Soo, Stone Jennifer S
Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology and Head and Neck Surgery, University of Washington, Seattle, Washington 98195-7923, USA.
Dev Dyn. 2007 Jan;236(1):156-70. doi: 10.1002/dvdy.21023.
In the avian inner ear, nonsensory supporting cells give rise to new sensory hair cells through two distinct processes: mitosis and direct transdifferentiation. Regulation of supporting cell behavior and cell fate specification during avian hair cell regeneration is poorly characterized. Expression of Atoh1, a proneural transcription factor necessary and sufficient for developmental hair cell specification, was examined using immunofluorescence in quiescent and regenerating hair cell epithelia of mature chickens. In untreated birds, Atoh1 protein was not detected in the auditory epithelium, which is quiescent. In contrast, numerous Atoh1-positive nuclei were seen in the utricular macula, which undergoes continual hair cell turnover. Atoh1-positive nuclei emerged in the auditory epithelium by 15 hr post-ototoxin administration, before overt hair cell damage and supporting cell re-entry into the cell cycle. Subsequently, Atoh1 labeling was seen in 15% of dividing supporting cells. During cell division, Atoh1 was distributed symmetrically to daughter cells, but Atoh1 levels were dramatically regulated shortly thereafter. After cellular differentiation, Atoh1 labeling was confined to hair cells regenerated through either mitosis or direct transdifferentiation. However, Atoh1 expression in dividing progenitors did not necessarily predict hair cell fate specification in daughter cells. Finally, predominant modes of hair cell regeneration varied significantly across the radial axis of the auditory epithelium, with mitosis most frequent neurally and direct transdifferentiation most frequent abneurally. These observations suggest a role for Atoh1 in re-specifying supporting cells and in biasing postmitotic cells toward the hair cell fate during hair cell regeneration in the mature chicken ear.
在鸟类内耳中，非感觉性支持细胞通过两种不同的过程产生新的感觉毛细胞：有丝分裂和直接转分化。在鸟类毛细胞再生过程中，支持细胞行为和细胞命运特化的调控特征尚不明确。使用免疫荧光法在成熟鸡的静止和再生毛细胞上皮中检测了Atoh1（一种对发育性毛细胞特化必需且充分的神经前体转录因子）的表达。在未经处理的鸟类中，在静止的听觉上皮中未检测到Atoh1蛋白。相比之下，在经历持续毛细胞更新的椭圆囊斑中可见大量Atoh1阳性细胞核。耳毒素给药后15小时，听觉上皮中出现Atoh1阳性细胞核，此时尚未出现明显的毛细胞损伤以及支持细胞重新进入细胞周期。随后，在15%进行分裂的支持细胞中可见Atoh1标记。在细胞分裂过程中，Atoh1对称地分布到子细胞中，但此后不久Atoh1水平受到显著调控。细胞分化后，Atoh1标记局限于通过有丝分裂或直接转分化再生的毛细胞。然而，分裂祖细胞中Atoh1的表达并不一定能预测子细胞中的毛细胞命运特化。最后，毛细胞再生的主要模式在听觉上皮的径向轴上有显著差异，有丝分裂在神经侧最频繁，直接转分化在离神经侧最频繁。这些观察结果表明，Atoh1在成熟鸡耳毛细胞再生过程中，对于重新指定支持细胞以及使有丝分裂后细胞偏向毛细胞命运方面发挥作用。
