Roberts Richard, Elsner Jeffrey, Bagnall Martha W
Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, CB 8108, St. Louis, MO, 63110, USA.
J Assoc Res Otolaryngol. 2017 Jun;18(3):415-425. doi: 10.1007/s10162-017-0617-9. Epub 2017 Mar 22.
What is the role of normally patterned sensory signaling in development of vestibular circuits? For technical reasons, including the difficulty in depriving animals of vestibular inputs, this has been a challenging question to address. Here we take advantage of a vestibular-deficient zebrafish mutant, rock solo , in order to examine whether normal sensory input is required for formation of vestibular-driven postural circuitry. We show that the rock solo mutant is a splice site mutation in the secreted glycoprotein otogelin (otog), which we confirm through both whole genome sequencing and complementation with an otog early termination mutant. Using confocal microscopy, we find that elements of postural circuits are anatomically normal in rock solo mutants, including hair cells, vestibular ganglion neurons, and vestibulospinal neurons. Surprisingly, the balance and postural deficits that are readily apparent in younger larvae disappear around 2 weeks of age. We demonstrate that this behavioral recovery follows the delayed development of the anterior (utricular) otolith, which appears around 14 days post-fertilization (dpf), compared to 1 dpf in WT. These findings indicate that utricular signaling is not required for normal structural development of the inner ear and vestibular nucleus neurons. Furthermore, despite the otolith's developmental delay until well after postural behaviors normally appear, downstream circuits can drive righting reflexes within ∼1-2 days of its arrival, indicating that vestibular circuit wiring is not impaired by a delay in patterned activity. The functional recovery of postural behaviors may shed light on why humans with mutations in otog exhibit only subclinical vestibular deficits.
正常模式的感觉信号在前庭回路发育中起什么作用?由于技术原因,包括剥夺动物前庭输入的困难,这一直是一个具有挑战性的问题。在这里,我们利用一种前庭缺陷的斑马鱼突变体rock solo,来研究前庭驱动的姿势回路形成是否需要正常的感觉输入。我们发现rock solo突变体是分泌型糖蛋白耳胶蛋白(otogelin,otog)中的一个剪接位点突变,我们通过全基因组测序和与otog早期终止突变体互补来证实这一点。使用共聚焦显微镜,我们发现姿势回路的元件在rock solo突变体中在解剖学上是正常的,包括毛细胞、前庭神经节神经元和前庭脊髓神经元。令人惊讶的是,在幼体中明显的平衡和姿势缺陷在大约2周龄时消失。我们证明这种行为恢复伴随着前(椭圆囊)耳石的延迟发育,耳石在受精后约14天(dpf)出现,而野生型在1 dpf出现。这些发现表明椭圆囊信号对于内耳和前庭核神经元的正常结构发育不是必需的。此外,尽管耳石的发育延迟到姿势行为正常出现之后很久,但下游回路在其出现后的约1 - 2天内就能驱动翻正反射,这表明前庭回路布线不会因模式化活动的延迟而受损。姿势行为的功能恢复可能有助于解释为什么otog基因突变的人类仅表现出亚临床前庭缺陷。
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