Molecular Basis For The Morphogenesis Of The Inner Ear

内耳形态发生的分子基础

• 批准号: 8349617
• 负责人: Doris Wu
• 金额: $ 182.36万
• 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/8349617
• 关键词: Alleles; Anterior; Apical; Area; Auditory; Binding; Cell Cycle; Cell Differentiation process; Cell surface; Cessation of life; Chickens; Cochlea; Cochlear duct; Complex; Crista ampullaris; Development; Developmental Process; Drosophila genus; Dysplasia; Ear; Embryo; Embryonic Development; Endolymphatic duct; Eph Family Receptors; Ephrins; Epithelial; Epithelium; Equilibrium; Erinaceidae; Family; Ganglia; Genes; Genetic; Genetic Transcription; Goals; Hair Cells; Hearing; Homeostasis; Human; Knowledge; Labyrinth; Length; Ligands; Liquid substance; Manuscripts; Mesenchymal; Mitosis; Mitotic; Molecular; Morphogenesis; Mus; Organ; Organ of Corti; Pathologic Processes; Pattern; Physiological Processes; Play; Point Mutation; Preparation; Protein Tyrosine Kinase; Proteins; Publishing; Regulation; Relative (related person); Role; Sensory; Sensory Hair; Signal Transduction; Signaling Molecule; Stapes; Structure; System; Technology; Tertiary Protein Structure; Time; Tissues; Tretinoin; Up-Regulation; base; capsule; cell type; cellular development; deafness; design; homeodomain; interest; loss of function; malformation; member; morphogens; mutant; premature; prospective; relating to nervous system; sample fixation; transcription factor

This years major accomplishments are in the following areas: 1)Sonic hedgehog from the auditory ganglion regulates the length of the cochlear duct and the timing of hair cell differentiation (manuscript in preparation) The mammalian hearing apparatus, the organ of corti, is tonotopically organized. An interesting feature of the organ of Corti formation is that cell cycle exit of sensory hair cells is initiated at the apex of the cochlear duct and proceeds towards the base. In contrast, hair cell differentiation starts from the base and progresses towards the apex after cell cycle exit is completed. Thus, sensory hair cell differentiation in the apical cochlear duct is normally delayed after terminal mitosis, relative to the base. This unconventional cellular development may provide some of the anatomical bases for cochlear tonotopy. Based on expression studies, it has been proposed that Sonic hedgehog (Shh) expressed in the auditory ganglion plays a role in delaying the differentiation of post-mitotic hair cell in the apex. Our results of targeted deletion of Shh in the auditory ganglion indicated that the cochlear duct of conditional mutants is shorter and it shows a premature expression of Atoh1 in the organ of Corti. While the negative regulation of Atoh1 by Shh supports the notion that Shh is involved in the timing of hair cell differentiation, the progression of differentiation is similar between wildtype and mutant cochlea, suggesting other factors are responsible for the selective delay of hair cell differentiation in the apex of the cochlear duct. 2)Genetic interaction of Lmx1a and Lmo4 in patterning the vestibular system (manuscript in preparation) LIM-homeodomain (LIM-HD) transcription factors are critical for formation of multiple organs. In Drosophila, the activities of LIM-HD are regulated by a family of LIM-only domain proteins, which compete with LIM-HD for their binding partners and thereby down-regulating LIM-HD activated transcription. Lmx1a is a member of the LIM-HD transcription factors, which is important for inner ear formation. In dreher mutants, in which a point mutation in Lmx1a created a functional null allele, the inner ear does not form properly but all the sensory patches are present within the membranous epithelium. In contrast, Lmo4, one of the LIM-only proteins expressed in the developing inner ear, is required for the formation of the three sensory organs, cristae. We demonstrated that Lmx1a and Lmo4 genetically interact with each other. The absence of crista formation in Lmo4 null mutants is partially or fully rescued in the genetic background of one or both alleles of dreher, respectively. Based on these results, we propose that Lmx1a activities in the prospective cristae are normally negatively regulated by Lmo4 in order for sensory tissue development to proceed. 3)Requirement of Ephrinb2 in ear development The Eph family of receptor tyrosine kinases and their cell surface-bound ephrin ligands are implicated in a wide range of developmental, physiological, and pathological processes in many cell types and organs. Despite efforts begun over a decade ago to elucidate the expression patterns of these important signaling molecules in the auditory and vestibular systems, knowledge of their functional significance in hearing and balance remains rudimentary. We investigated the effects of ephrinb2 (efnb2) loss-of-function on the murine ear using Cre-LoxP technology, as efnb2 null homozygosity results in early embryonic death. Using multiple Cre drivers with activities in different tissues of the developing ear, we have defined a spectrum of abnormalities remarkably similar to that of the human Mondini dysplasia or EVA (enlarged endolymphatic duct, cochlear hypoplasia, and variably penetrant stapes fixation to the otic capsule). More specifically, we have identified a distended endolymphatic duct and otoconial abnormalities as resulting from a loss of otic epithelial (rather than mesenchymal) efnb2. Loss of otic epithelial efnb2 also causes dysregulation of the pendrin (SLC26A4) gene, which encodes a transporter required for proper inner ear fluid homeostasis in humans. 4)Anterior and posterior polarity of the inner ear is established by retinoic acid signaling (manuscript published) Retinoic acid (RA) is an important morphogen during embryogenesis. Using gain- and loss- of function approaches in chicken and mice, we show that RA signaling at a distance establishes the anterior-posterior axis of the inner ear. A higher level of RA signaling within the otic epithelium is required to pattern the posterior, non-sensory fates via upregulation of the gene Tbx1, whereas the anterior otic region requires relatively lower levels of RA signaling than the posterior for establishing the neural-sensory fates.

今年的主要成绩有以下几个方面： 1）来自听觉神经节的音刺猬调节耳蜗管的长度和毛细胞分化的时间（手稿正在准备中） 哺乳动物的听觉器官，即柯蒂氏器，是按音调组织的。柯蒂形成器官的一个有趣特征是感觉毛细胞的细胞周期退出在耳蜗管的顶端开始并向基部进行。 相反，毛细胞分化从基部开始，并在细胞周期退出完成后向顶端进展。 因此，相对于基部，顶端耳蜗管中的感觉毛细胞分化通常在终末有丝分裂后延迟。这种非常规的细胞发育可能为耳蜗音调提供一些解剖学基础。基于表达研究，有人提出，在听觉神经节中表达的声波刺猬（Shh）在延迟顶端有丝分裂后毛细胞的分化中发挥作用。 我们在听神经节中定向删除Shh的结果表明，条件突变体的耳蜗管较短，并且显示出Atoh1在Corti器官中的过早表达。虽然Shh对Atoh1的负调节支持Shh参与毛细胞分化时间的观点，但野生型和突变型耳蜗之间的分化进程相似，这表明其他因素导致毛细胞分化的选择性延迟。耳蜗导管的顶端。 2）Lmx1a和Lmo4在前庭系统模式中的遗传相互作用（手稿正在准备中） LIM-同源域 (LIM-HD) 转录因子对于多个器官的形成至关重要。 在果蝇中，LIM-HD 的活性受到 LIM-only 结构域蛋白家族的调节，这些蛋白与 LIM-HD 竞争其结合伴侣，从而下调 LIM-HD 激活的转录。 Lmx1a 是 LIM-HD 转录因子的成员，对于内耳的形成非常重要。 在 Dreher 突变体中，Lmx1a 的点突变产生了功能性无效等位基因，内耳无法正常形成，但所有感觉斑块都存在于膜上皮内。 相比之下，Lmo4 是发育中的内耳中表达的仅 LIM 蛋白之一，它是三个感觉器官（嵴）的形成所必需的。 我们证明了 Lmx1a 和 Lmo4 在基因上相互作用。 Lmo4无效突变体中嵴形成的缺失在dreher的一个或两个等位基因的遗传背景下分别被部分或完全拯救。基于这些结果，我们提出，为了促进感觉组织的发育，预期嵴中的 Lmx1a 活性通常受到 Lmo4 的负调控。 3）Ephrinb2在耳朵发育中的需要 Eph 受体酪氨酸激酶家族及其细胞表面结合的肝配蛋白配体与许多细胞类型和器官的广泛发育、生理和病理过程有关。 尽管十多年前就开始努力阐明这些重要信号分子在听觉和前庭系统中的表达模式，但对其在听力和平衡方面的功能意义的了解仍然很初级。 我们使用 Cre-LoxP 技术研究了 ephrinb2 (efnb2) 功能丧失对小鼠耳朵的影响，因为 efnb2 纯合性缺失会导致早期胚胎死亡。 使用多个 Cre 驱动器在发育中的耳朵的不同组织中进行活动，我们定义了一系列与人类 Mondini 发育不良或 EVA 非常相似的异常（内淋巴管扩大、耳蜗发育不全以及不同程度的穿透性镫骨固定在耳囊上） 。 更具体地说，我们已经确定内淋巴管扩张和耳圆锥异常是由于耳上皮（而不是间质）efnb2 损失所致。 耳上皮 efnb2 的缺失还会导致 pendrin (SLC26A4) 基因失调，该基因编码人类内耳液体稳态所需的转运蛋白。 4）内耳的前极性和后极性是通过视黄酸信号建立的（手稿已发表） 视黄酸（RA）是胚胎发生过程中重要的形态发生素。通过对鸡和小鼠进行功能获得和丧失的方法，我们发现远距离的 RA 信号传导建立了内耳的前后轴。 耳上皮内需要更高水平的 RA 信号传导，通过 Tbx1 基因的上调来形成后部非感觉命运，而前耳区域需要相对较低水平的 RA 信号传导来建立神经感觉命运。 。