Molecular Basis For The Morphogenesis Of The Inner Ear

内耳形态发生的分子基础

• 批准号: 6674016
• 负责人: Doris Wu
• 金额: --
• 依托单位: NATIONAL INSTITUTE ON DEAFNESS AND OTHER COMMUNICATION DISORDERS
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6674016
• 关键词: Retroviridae; bone morphogenetic proteins; cell differentiation; chick embryo; developmental genetics; developmental neurobiology; gene expression; gene targeting; genetic mapping; histogenesis; histopathology; laboratory mouse; labyrinth; otocyst /otolith; transfection /expression vector; transforming growth factors

Proper patterning of the inner ear requires instructive signaling from surrounding tissues including the hindbrain, mesoderm and notochord. The molecular mechanisms underlying these inductive events are largely unknown. One of our major accomplishments this year (in collaboration with Dr. Douglas Epstein at the University of Pennsylvania) was to demonstrate that Sonic Hedgehog (Shh) is an important signal in specifying the inner ear. The ventral portion of the neural tube (floor plate) and the notochord are thought to be the primary sources of SHH for the inner ear. In Shh knock out mice, ventral inner ear structures such as the saccule and cochlea fail to develop. Medial and lateral structures such as the endolymphatic duct and lateral canal, appear to be specified initially but fail to develop at later stages. The process of neuroblast delamination from the anterior region of the otocyst to form the cochleovestibular ganglion is also affected in the Shh mutants. Gene expression analyses of Shh knock out mutant mice as well as transgenic mice that ectopically express Shh in the otocyst show that several genes such as Ngn1, Pax2, Otx2, Tbx1, and Brn4 are likely downstream targets of SHH. Another long-standing interest in the laboratory is to investigate the role of Bone Morphogenetic Proteins (BMPs) in the developing inner ear. Various Bmps are expressed in the developing otic epithelium and regions of surrounding mesenchyme during different stages of development. Previously, we have shown that BMPs are important for the semicircular canal development as well as the formation of the otic capsule. During this year, by correlating the expression patterns of various BMPs with the localization of cells responding to them, we postulated that BMPs mediate epithelial to mesenchymal interactions in specific regions of the inner ear such as the endolymphatic duct and semicircular canals. Furthermore, the formation of sensory and non-sensory components of the inner ear are most likely coupled during development, even though the molecular mechanisms involved in this coordination are largely unknown. FGF-3 and 10 (Fibroblast growth factor) are expressed in the presumptive sensory organs while one of their receptors, FGFR2-IIIb, is primarily expressed in the non-sensory epithelium. These patterns suggest that FGFs in the sensory organ could play such a role in coordinating sensory and non-sensory development. Using a recombinant avian retrovirus encoding FGF-3 or beads soaked with FGF-2, we showed that FGFs promote canal development in the chicken inner ear. These effects of FGFs are mediated by induction of Bmp2 in the canal pouch region, thus identifying a molecular pathway whereby sensory tissue can induce non-sensory development.

内耳的正确模式需要来自周围组织（包括后脑、中胚层和脊索）的指导性信号。这些诱导事件背后的分子机制很大程度上是未知的。我们今年的主要成就之一（与宾夕法尼亚大学的 Douglas Epstein 博士合作）是证明 Sonic Hedgehog (Shh) 是指定内耳的重要信号。神经管（底板）的腹侧部分和脊索被认为是内耳 SHH 的主要来源。在 Shh 基因敲除小鼠中，腹侧内耳结构（例如球囊和耳蜗）无法发育。内侧和外侧结构，例如内淋巴管和外侧管，最初似乎是特定的，但在后期阶段未能发育。在Shh突变体中，神经母细胞从耳囊前部区域分层形成耳蜗前庭神经节的过程也受到影响。对 Shh 敲除突变小鼠以及在耳囊中异位表达 Shh 的转基因小鼠进行的基因表达分析表明，Ngn1、Pax2、Otx2、Tbx1 和 Brn4 等多个基因可能是 SHH 的下游靶标。 实验室长期以来的另一个兴趣是研究骨形态发生蛋白（BMP）在内耳发育中的作用。在不同的发育阶段，不同的 Bmp 在发育中的耳上皮和周围间质区域中表达。之前，我们已经证明 BMP 对于半规管发育以及耳囊的形成很重要。今年，通过将各种 BMP 的表达模式与对其作出反应的细胞的定位相关联，我们推测 BMP 介导内耳特定区域（如内淋巴管和半规管）上皮与间质的相互作用。 此外，内耳感觉和非感觉成分的形成很可能在发育过程中耦合，尽管这种协调所涉及的分子机制在很大程度上是未知的。 FGF-3 和 10（成纤维细胞生长因子）在假定的感觉器官中表达，而它们的受体之一 FGFR2-IIIb 主要在非感觉上皮中表达。这些模式表明感觉器官中的 FGF 在协调感觉和非感觉发育中发挥着这样的作用。使用编码 FGF-3 的重组禽逆转录病毒或浸泡有 FGF-2 的珠子，我们发现 FGF 促进鸡内耳的耳道发育。 FGF 的这些作用是通过在管袋区域诱导 Bmp2 介导的，从而确定了感觉组织可诱导非感觉发育的分子途径。