Molecular Basis For The Morphogenesis Of The Inner Ear

内耳形态发生的分子基础

基本信息

批准号：
10001922
负责人：
Doris Wu
金额：
$ 176.39万
依托单位：
NATIONAL INSTITUTE ON DEAFNESS AND OTHER COMMUNICATION DISORDERS
依托单位国家：
美国
项目类别：
财政年份：
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/10001922
关键词：
Acceleration Adopted Afferent Neurons Animals Anterior Area Auditory Behavioral Brain Brain Stem Cell physiology Cerebellum Clinical Code Complex Crista ampullaris Cytochrome P450 Defect Development Dorsal Dyes Ear Enzymes Epithelial Epithelial Cells Epithelium Equilibrium Etiology Evoked Potentials Exhibits Functional disorder Gene Expression Genes Genetic Genetic Predisposition to Disease Genetic Transcription Goals Growth Hair Hair Cells Head Head Movements Human Hyperactive behavior Journals Knock-out Knockout Mice Labyrinth Manuscripts Mediating Molecular Morphogenesis Motor Activity Mus Mutant Strains Mice NTN1 gene Nerve Endings Neuraxis Neurons Organ Pathology Patients Pattern Peripheral Phenotype Physiological Population Positioning Attribute Process Property Publishing Reaction Time Semicircular canal structure Sensory Sensory Hair Signal Transduction Structure Surface Syndrome System Therapeutic Thinness Tissues Tretinoin Utricular macula Vestibule Water Work base bone morphogenetic protein 2 deafness design emx2 protein gain of function genetic analysis hearing impairment inner ear development insight lateral line lipophilicity macula malformation millisecond mouse model mutant nerve supply neuromast otoconia pressure prospective response saccule macula sensory input sound transcription factor vestibular reflex

项目摘要

This years major accomplishments are in the following areas: 1) Genetic interactions support an inhibitory relationship between Bone morphogenetic protein 2 and Netrin 1 during semicircular canal formation. The three semicircular canals of the mammalian ear are the non-sensory components of the vestibular apparatus responsible for detecting angular acceleration. Malformations such as truncation or thinning of one of these canals will result in balancing deficits in mice. In humans, superior canal dehiscence is a syndrome associated with defects of the anterior canal during development, but the underlying genetic etiology is unknown. A better understanding of the molecular mechanisms underlying normal canal formation will provide insights into the genetics and pathology associated with the vestibular system in humans. Developmentally, the three semicircular canals are derived from two epithelial out-pockets of the otocyst. In these out-pockets, the opposing epithelia in each prospective canal move towards each other to form a fusion plate and the epithelial cells in the fusion plate resorb, leaving behind the rim of the out-pocket to form an arc-shaped canal. As a result, a canal will not form if the canal pouch fails to grow properly. Despite the presence of a canal pouch, extensive resorption in the fusion plate can chew away too much epithelial cells and leads to absence of a canal as well. In this study, we show that Bone morphogenetic protein 2 (Bmp2) expressed in both the center epithelia and the rim of the canal pouch is important for canal formation. In Bmp2 conditional knockout mouse mutants, all three semicircular canals are missing but the ampullae, which house the sensory tissue for the canals, the cristae, are normal. To investigate the cause of this phenotype, we conducted gene expression and genetic analyses. Our results suggest that Bmp2 has a dual function in canal formation. It functions to inhibit the resorption process by inhibiting the expression of a gene, Netrin1, which is important for mediating resorption. Concomitantly, it also functions to promote the growth of the canal rim. This work has been published in the journal, Development. doi:10.1242/dev.174748 2) Selectivity of afferent neurons by Emx2 in vestibular maculae of the inner ear All sensory end-organs need to be properly connected to the central nervous system by sensory neurons before sensory inputs can be interpreted in a meaningful manner. Understanding the mechanisms involved in this proper wiring during development is important from a functional standpoint. The lateral line system of aquatic animals, which functions to detect water pressure, is comprised of neuromasts that are studded along the surface of the animals body. Each neuromast consists of two groups of sensory hair cells, in which each group consists hair bundles that are oriented in opposite direction from the other group, organized along either the anterior-posterior or dorsal-ventral axis of the body. Notably, the neurons that innervate the two populations of hair cells within each neuromast are also segregated such that a single neuron only innervate hair cells that share the same bundle orientation. Previously, we have shown that the transcription factor Emx2 expressed only in hair cells that share the same orientation within a neuromast is important for mediating both the hair bundle orientation as well as the neuronal selectivity of the hair cells. Although both hair bundle orientation and selection of neuronal targets require Emx2, our results suggest that the two cellular processes are independently regulated by different transcription targets of Emx2. In the vestibular maculae of the mouse inner ear, the transcription factor Emx2 is also important for reversing hair bundle orientation from it default position by 180 degrees and thus establishes the line of polarity reversal (LPR) in the maculae. Interestingly, the neuronal innervation pattern in the two maculae appears to be segregated according to the LPR as well. Neurons that innervate hair cells in the Emx2-positive regions of the utricular and saccular macula, have central projections to the cerebellum, whereas neurons in the Emx2-negative regions project to the brainstem. Using lipophilic dye tracing and genetic mouse models, we are currently investigating the neuronal innervation pattern and the functional consequences of maculae in Emx2 knockout and gain-of-function mutants. 3) Cytochrome P450 26b1-mediated specification of vestibular striola and central zones is required for transient responses in linear acceleration The vestibular system of the inner ear is important for maintaining our sense of balance. Understanding how head movements and positional information are being coded by the vestibular sensory organs and relayed to the brain is important from both clinical and therapeutic perspectives. Two types of sensory organs are present in the vestibular system of the mammalian inner ear: cristae and maculae. The three cristae are responsible for detecting angular acceleration, whereas the two maculae, macula of the utricle and saccule, are responsible for detecting linear acceleration. A specialized region is present in each of the vestibular organ known as the central zone in the cristae and striola in the maculae. A defining feature of the striola/central zones is the calyceal nerve endings of afferent neurons that often encase multiple hair cells. The precise function of these complex calyces is not known but based on physiological properties of the hair cells and sensory neurons in these regions, it has been postulated that these regions are responsible of rapid signaling and important for mediating vestibular reflexes, which are extremely fast with response time of milliseconds in some species. Our study shows that formation of the striola/central zone is dependent on the presence of a Retinoic acid (RA) degradation enzyme, Cyp26b1, in the prospective striola/central zones during development, which functions to reduce the amount of RA emanating from the surrounding sensory tissues in the extrastriolar/peripheral zones. We generated Cyp26b1 conditional knockout (cKO) mice and based on the molecular, cellular and physiological analyses, we show that striola/central zones have adopted extrastriolar and peripheral zone-like properties in Cyp26b1 cKO mutants. To our surprise, behavioral and functional analyses of these Cyp26b1 cKO mice indicate that the striola/central zones are not required for mediating vestibular reflexes. Instead, our results show that the striola in the two maculae are responsible for generating the vestibular evoked potential, which is an assessment for macular functions. Although these mice exhibit no obvious deficits that are associated with vestibular dysfunctions such as circling, head bobbing or hyperactivity, they have difficulty in traversing the balance beam, suggesting that the striola/central zones are important for coordinating challenging vestibular and motor activities. A manuscript of this work is available on BioRxiv, doi: http://dx.doi.org/10.1101/726232.

今年的主要成就在以下领域： 1）遗传相互作用支持半圆形管形成期间骨形态发生蛋白2和Netrin 1之间的抑制关系。哺乳动物耳朵的三个半圆形管是负责检测角加速度的前庭设备的非感官成分。这些运河之一的截断或变薄等畸形将导致小鼠的缺陷。在人类中，上管裂开是一种与发育过程中前管缺陷相关的综合征，但是潜在的遗传病因尚不清楚。对正常运河形成的分子机制有更好的了解将为与人类前庭系统相关的遗传学和病理提供见解。从发展上讲，这三个半圆形管是源自耳细胞的两个上皮偏口。在这些外部袋中，每个前瞻性运河中的相对上皮相互向彼此移动，形成融合板和融合板上的上皮细胞，留下了支出的边缘，形成了弧形的管子。结果，如果运河袋无法正常生长，则不会形成运河。尽管存在运河袋，但融合板中的广泛吸收仍会咀嚼过多的上皮细胞，并且也导致没有运河。在这项研究中，我们表明在中心上皮和运河袋的边缘表达的骨形态发生蛋白2（BMP2）对于运河形成很重要。在BMP2有条件的敲除小鼠突变体中，所有三个半圆形管都缺失了，但是容纳运河的感觉组织Cristae的截肢是正常的。为了研究这种表型的原因，我们进行了基因表达和遗传分析。我们的结果表明，BMP2在运河形成中具有双重功能。它通过抑制基因Netrin1的表达来抑制吸收过程，这对于介导吸收很重要。同时，它也起到促进运河边缘的生长的作用。这项工作已发表在《开发期刊》上。 doi：10.1242/dev.174748 2）EMX2在内耳的前庭斑点中对传入神经元的选择性在感觉输入可以以有意义的方式解释感官输入之前，所有感觉末端都需要通过感觉神经元正确连接到中枢神经系统。从功能的角度来看，在开发过程中了解这种正确接线所涉及的机制很重要。水生动物的横向线系统可检测水压，由沿着动物体面的神经瘤组成。每个神经瘤都由两组感觉毛细胞组成，其中每组沿着与另一组相反的方向束缚，沿着身体的前后或背腹轴组织。值得注意的是，支配每个神经瘤中两个毛细胞种群的神经元也被隔离，使得单个神经元仅支配具有相同束方向的毛细胞。以前，我们已经表明，仅在神经瘤中共享相同方向的毛细胞中表达的转录因子EMX2对于介导毛发束方向以及毛细胞的神经元选择性很重要。尽管头发束取向和神经元靶标的选择都需要EMX2，但我们的结果表明，这两个细胞过程均由EMX2的不同转录靶标独立地调节。在小鼠内耳的前庭黄斑中，转录因子EMX2对于将头发束取向从其默认位置逆转180度也很重要，因此在黄斑中建立了极性反转（LPR）的线。有趣的是，根据LPR，两个斑驳中的神经元神经神经模式似乎也被隔离。神经元素在尿布和糖果黄斑的EMX2阳性区域支配毛细胞的神经元具有对小脑的中心投射，而EMX2阴性区域的神经元则向脑干投射。使用亲脂性染料痕迹和遗传小鼠模型，我们目前正在研究EMX2敲除和功能增益突变体中MACULAE的神经元神经支配模式和功能后果。 3）细胞色素P450 26B1介导的前庭striola和中央区域的瞬时响应是线性加速度的瞬态响应所必需的内耳的前庭系统对于保持我们的平衡感很重要。从临床和治疗的角度来看，了解前庭感觉器官的头部运动和位置信息如何编码并传达给大脑。哺乳动物内耳的前庭系统中存在两种类型的感觉器官：cristae和maculae。这三个Cristae负责检测角加速度，而两个黄斑和糖果的黄斑则负责检测线性加速度。在每个被称为cristae的中央区域的前庭器官中，都存在一个专门的区域，在麦芽膜中的striola中存在一个专门区域。 Striola/Central区的一个定义特征是传入神经元的钙化神经末端，这些神经元通常包含多个毛细胞。这些复杂的钙的精确功能尚不清楚，但基于这些区域中毛细胞和感觉神经元的生理特性，已经假定这些区域是导致快速信号传导的原因，对于介导前庭反射而言很重要，这些区域在某些物种中与毫秒的响应时间非常快。我们的研究表明，Striola/Central区的形成取决于在发育过程中前瞻性striola/Central区域中的视黄酸（RA）降解酶CYP26B1的存在，这起作用可减少外交/外交/外围脑周围感觉组织中的RA量。我们产生了CYP26B1条件基因敲除（CKO）小鼠，并基于分子，细胞和生理分析，我们表明Striola/Central区已在CYP26B1 CKO突变体中采用了骨化区/中心区域的外层和外围区。令我们惊讶的是，这些CYP26B1 CKO小鼠的行为和功能分析表明，介导前庭反射不需要Striola/Central区域。取而代之的是，我们的结果表明，两个黄斑中的Striola负责产生前庭诱发的电位，这是对黄斑功能的评估。尽管这些小鼠没有与前庭功能障碍有关的明显缺陷，例如圆圈，摇动或多动症，但它们在遍历平衡梁方面遇到困难，这表明Striola/Central区域对于协调挑战性的前庭和运动活动很重要。这项工作的手稿可在doi：http：//dx.doi.org/10.1101/726232上获得。