Regulating dorsoventral polarity within the inner ear

描述(申请人提供)：内耳的听觉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。通过识别调控内耳形态发生的遗传网络，我们对耳廓发育和疾病之间的联系的理解应该会有所提高。听力的主要成分(耳蜗管)和平衡的主要成分(半规管、椭圆囊和球囊)分别由常见的两侧结构--耳囊的腹侧和背侧突起形成。内耳的听觉和前庭成分的组织依赖于耳囊中基因表达的局部模式。已知周围组织影响耳囊的分区，但参与的信号仍不清楚。脊索和底板是分泌蛋白Sonic hedgehog(Shh)的来源，Sonic hedgehog(Shh)在短程和长程信号事件中发挥作用，促进腹侧神经管和轴旁结构中前体细胞的生长和分化。在没有Shh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细胞不能发育。Shh-/-胚胎中内耳缺陷的起源可以归因于以前涉及到的耳蜗系、神经元系和软骨系的一些基因表达的改变。虽然Shh信号的作用在耳上皮细胞中被检测到，但邻近组织包括骨膜间充质和神经管也是Shh作用的靶点。 这让人质疑Shh信号在影响内耳发育的每个组织中的相对作用。这项建议中概述的实验旨在阐明Shh在腹侧耳囊中指定听觉细胞命运的机制。Hedgehog(HH)信号在内耳发育中的时间和空间需求将通过在每个组织中作用于耳囊的每个组织中的Smoothened条件失活来解决，Smoothens是所有HH信号的关键转导。还提出了识别Shh信号在耳廓发育中的下游效应的实验。最后，尽管初步了解了听觉细胞命运是如何确定的，但对在耳囊中建立前庭(背部)结构的外部线索知之甚少。使用转基因方法将特定的途径抑制剂引入背侧耳囊，以及对候选背侧因子中小鼠突变体的评估，应该有助于我们全面理解内耳背腹轴上的极性是如何建立的。

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.