PDF(Pubmed)
Abstract：
Rac small GTPases play important roles during embryonic development of the inner ear; however, little is known regarding their function in cochlear hair cells (HCs) after specification. Here, we revealed the localization and activation of Racs in cochlear HCs using GFP-tagged Rac plasmids and transgenic mice expressing a Rac1-fluorescence resonance energy transfer (FRET) biosensor. Furthermore, we employed Rac1-knockout (Rac1-KO, Atoh1-Cre;Rac1flox/flox) and Rac1 and Rac3 double KO (Rac1/Rac3-DKO, Atoh1-Cre;Rac1flox/flox;Rac3-/-) mice, under the control of the Atoh1 promoter. However, both Rac1-KO and Rac1/Rac3-DKO mice exhibited normal cochlear HC morphology at 13 weeks of age and normal hearing function at 24 weeks of age. No hearing vulnerability was observed in young adult (6-week-old) Rac1/Rac3-DKO mice even after intense noise exposure. Consistent with prior reports, the results from Atoh1-Cre;tdTomato mice confirmed that the Atoh1 promoter became functional only after embryonic day 14 when the sensory HC precursors exit the cell cycle. Taken together, these findings indicate that although Rac1 and Rac3 contribute to the early development of sensory epithelia in cochleae, as previously shown, they are dispensable for the maturation of cochlear HCs in the postmitotic state or for hearing maintenance following HC maturation. KEY MESSAGES: Mice with Rac1 and Rac3 deletion were generated after HC specification. Knockout mice exhibit normal cochlear hair cell morphology and hearing. Racs are dispensable for hair cells in the postmitotic state after specification. Racs are dispensable for hearing maintenance after HC maturation.
摘要：
Rac小GTP酶在内耳的胚胎发育过程中起着重要作用；然而，规范后，人们对它们在耳蜗毛细胞（HCs）中的功能知之甚少。这里,我们使用GFP标记的Rac质粒和表达Rac1荧光共振能量转移（FRET）生物传感器的转基因小鼠揭示了Racs在耳蜗HC中的定位和激活。此外，我们采用了Rac1敲除(Rac1-KO,Atoh1-Cre；Rac1flox/flox）和Rac1和Rac3双KO（Rac1/Rac3-DKO，Atoh1-Cre；Rac1flox/flox；Rac3-/-）小鼠，在Atoh1启动子的控制下。然而,Rac1-KO和Rac1/Rac3-DKO小鼠在13周龄时表现出正常的耳蜗HC形态，在24周龄时表现出正常的听力功能。即使在强烈的噪声暴露后，在年轻的成年（6周大）Rac1/Rac3-DKO小鼠中也没有观察到听力脆弱性。与以前的报告一致，Atoh1-Cre;tdTomato小鼠的结果证实，Atoh1启动子仅在胚胎第14天之后，当感觉HC前体退出细胞周期时，才具有功能。一起来看,这些发现表明，尽管Rac1和Rac3有助于耳蜗感觉上皮的早期发育，如前所述，它们对于有丝分裂后状态的耳蜗HC的成熟或HC成熟后的听力维持是必不可少的。关键信息:在HC规范后产生具有Rac1和Rac3缺失的小鼠。敲除小鼠表现出正常的耳蜗毛细胞形态和听力。在指定后的有丝分裂状态下，Racs对于毛细胞是可有可无的。在HC成熟后，Racs对于听力维持是不必要的。
