Matei V, Pauley S, Kaing S, Rowitch D, Beisel K W, Morris K, Feng F, Jones K, Lee J, Fritzsch B
Department of Biomedical Science, Creighton University, Omaha, Nebraska 68178, USA.
Dev Dyn. 2005 Nov;234(3):633-50. doi: 10.1002/dvdy.20551.
We investigated whether co-expression of Neurog 1 and Atoh 1 in common neurosensory precursors could explain the loss of hair cells in Neurog 1 null mice. Analysis of terminal mitosis, using BrdU, supports previous findings regarding timing of exit from cell cycle. Specifically, we show that cell cycle exit occurs in spiral sensory neurons in a base-to-apex progression followed by cell cycle exit of hair cells in the organ of Corti in an apex-to-base progression, with some overlap of cell cycle exit in the apex for both hair cells and spiral sensory neurons. Hair cells in Neurog 1 null mice show cell cycle exit in an apex-to-base progression about 1-2 days earlier. Atoh 1 is expressed in an apex-to-base progression rather then a base-to-apex progression as in wildtype littermates. We tested the possible expression of Atoh1 in neurosensory precursors using two Atoh 1-Cre lines. We show Atoh 1-Cre mediated beta-galactosidase expression in delaminating sensory neuron precursors as well as undifferentiated epithelial cells at E11 and E12.5. PCR analysis shows expression of Atoh 1 in the otocyst as early as E10.5, prior to any histology-based detection techniques. Combined, these data suggest that low levels of Atoh 1 exist much earlier in precursors of hair cells and sensory neurons, possibly including neurosensory precursors. Analysis of Atoh 1-Cre expression in E18.5 embryos and P31 mice reveal beta-galactosidase stain in all hair cells but also in vestibular and cochlear sensory neurons and some supporting cells. A similar expression of Atoh 1-LacZ exists in postnatal and adult vestibular and cochlear sensory neurons, and Atoh 1 expression in vestibular sensory neurons is confirmed with RT-PCR. We propose that the absence of NEUROG 1 protein leads to loss of sensory neuron formation through a phenotypic switch of cycling neurosensory precursors from sensory neuron to hair cell fate. Neurog 1 null mice show a truncation of clonal expansion of hair cell precursors through temporally altered terminal mitosis, thereby resulting in smaller sensory epithelia.
我们研究了Neurog 1和Atoh 1在共同的神经感觉前体细胞中的共表达是否可以解释Neurog 1基因敲除小鼠中毛细胞的缺失。使用BrdU对终末有丝分裂进行分析，支持了先前关于细胞周期退出时间的研究结果。具体而言，我们发现细胞周期退出在螺旋感觉神经元中以从基部到顶部的顺序发生，随后在柯蒂氏器中的毛细胞以从顶部到基部的顺序发生细胞周期退出，毛细胞和螺旋感觉神经元在顶部的细胞周期退出存在一些重叠。Neurog 1基因敲除小鼠中的毛细胞在大约提前1 - 2天以从顶部到基部的顺序出现细胞周期退出。Atoh 1的表达是以从顶部到基部的顺序，而不是像野生型同窝小鼠那样以从基部到顶部的顺序。我们使用两种Atoh 1 - Cre系测试了Atoh1在神经感觉前体细胞中的可能表达。我们发现在E11和E12.5时，Atoh 1 - Cre介导的β - 半乳糖苷酶在正在分层的感觉神经元前体细胞以及未分化的上皮细胞中表达。PCR分析显示早在E10.5时，在内耳囊中就有Atoh 1的表达，这早于任何基于组织学的检测技术。综合这些数据表明，在毛细胞和感觉神经元的前体细胞中，可能包括神经感觉前体细胞，Atoh 1的低水平表达存在得更早。对E18.5胚胎和P31小鼠中Atoh 1 - Cre表达的分析显示，β - 半乳糖苷酶染色存在于所有毛细胞中，也存在于前庭和耳蜗感觉神经元以及一些支持细胞中。在出生后和成年的前庭和耳蜗感觉神经元中存在类似的Atoh 1 - LacZ表达，并且通过RT - PCR证实了前庭感觉神经元中Atoh 1的表达。我们提出，NEUROG 1蛋白的缺失通过使循环的神经感觉前体细胞从感觉神经元命运向毛细胞命运的表型转换，导致感觉神经元形成的丧失。Neurog 1基因敲除小鼠通过暂时改变终末有丝分裂，显示出毛细胞前体克隆扩增的截断，从而导致较小的感觉上皮。
