Regulating dorsoventral polarity within the inner ear

描述（由申请人提供）：内耳的听觉结构和前庭结构分别调节我们的听觉和平衡感。最近在确定人类遗传性耳聋和前庭疾病的一些原因方面取得了进展；然而，对协调内耳发育的遗传途径的详细了解仍然有限。通过识别调节内耳形态发生的遗传网络，我们对耳发育与疾病之间关系的理解应该会得到改善。听觉（耳蜗）和平衡（半规管、椭圆囊和球囊）的主要组成部分分别由共同的双侧结构耳囊的腹侧和背侧生长形成。内耳组织为听觉和前庭部分取决于耳囊内基因表达的局部模式。已知周围组织会影响耳囊的区室化，但参与信号仍不清楚。脊索和底板是分泌蛋白 Sonic hedgehog (Shh) 的来源，该蛋白在短程和长程信号传导事件中发挥作用，促进腹侧神经管和近轴结构中祖细胞的生长和分化。在缺乏“嘘”的情况下，包括耳蜗管和耳蜗前庭神经节在内的腹侧耳衍生物无法发育。 Shh -/- 胚胎中内耳缺陷的起源可归因于先前与耳蜗、神经元和软骨形成谱系的规范有关的许多基因表达的改变。尽管在耳上皮中检测到了Shh信号传导的影响，但包括周膜间质和神经管在内的邻近组织也是Shh作用的目标。 这引起了人们对影响内耳发育的每个组织中Shh信号传导的相对贡献的质疑。该提案中概述的实验旨在阐明 Shh 指定腹侧耳囊中听觉细胞命运的机制。内耳发育中 Hedgehog (Hh) 信号传导的时间和空间要求将通过 Smoothened 的有条件失活来解决，Smoothened 是影响耳囊的每个组织中所有 Hh 信号的重要传感器。 还提出了鉴定耳发育中 Shh 信号下游效应器的实验。最后，尽管对听觉细胞命运如何指定有初步了解，但对于在耳囊中建立前庭（背侧）结构的外在线索知之甚少。 使用转基因方法将特定途径抑制剂引入背侧耳囊，以及评估候选背侧化因子中的小鼠突变体，应有助于我们全面了解极性是如何沿内耳背腹轴建立的。

DESCRIPTION (provided by applicant): The auditory and vestibular structures of the inner ear mediate our senses of hearing and balance, respectively. Recent progress has been made in identifying some of the causes of hereditary forms of deafness and vestibular disease in humans; however, a detailed understanding of the genetic pathways coordinating inner ear development remains limited. By identifying the genetic networks regulating inner ear morphogenesis, our understanding of the association between otic development and disease should improve. The principal components for hearing (the cochlea) and balance (the semicircular canals, utricle and saccule) are formed from ventral and dorsal outgrowths, respectively, of a common bilateral structure, the otocyst. Organization of the inner ear into auditory and vestibular components is dependent on localized patterns of gene expression within the otic vesicle. Surrounding tissues are known to influence compartmentalization of the otic vesicle, yet the participating signals remain unclear. The notochord and floor plate are sources of the secreted protein Sonic hedgehog (Shh) that functions in both short and long range signaling events to promote growth and differentiation of progenitor cells in the ventral neural tube and paraxial structures. In the absence of Shh, ventral otic derivatives including the cochlear duct and cochleovestibular ganglia fail to develop. The origin of the inner ear defects in Shh -/- embryos can be attributed to alterations in the expression of a number of genes previously implicated in the specification of cochlear, neuronal and chondrogenic lineages. Although the effects of Shh signaling are detected in the otic epithelium, adjacent tissues including the periotic mesenchyme and neural tube are also targets of Shh action. This brings into question the relative contribution of Shh signaling in each of the tissues impacting on inner ear development. Experiments outlined in this proposal are aimed at elucidating the mechanism by which Shh specifies auditory cell fates in the ventral otocyst. The temporal and spatial requirements of Hedgehog (Hh) signaling in inner ear development will be addressed by the conditional inactivation of Smoothened, an essential transducer of all Hh signals, in each of the tissues impacting on the otic vesicle. Experiments to identity the downstream effectors of Shh signaling in otic development are also proposed. Finally, despite preliminary insights into how auditory cell fates are specified, little is known of the extrinsic cues that establish vestibular (dorsal) structures in the otic vesicle. Introduction of specific pathway inhibitors into the dorsal otocyst using transgenic approaches as well as the assessment of mouse mutants in candidate dorsalizing factors should contribute towards our overall understanding of how polarity is established along the dorsoventral axis of the inner ear.