The role of Eph/ephrin interactions in the development of inner ear innervation

内耳是一个高度复杂的结构和功能结构，它被精心组织以探测声音和运动，然而它是从简单的上皮细胞片发育而来的。在发育过程中，这种上皮必须产生和组织成熟器官中发现的所有主要细胞类型，包括专门检测声音或运动的感觉毛细胞，支持感觉细胞功能的非感觉细胞以及连接器官和中枢神经系统的神经元。感觉细胞检测到声音或运动刺激，并将其转化为信号，通过神经元发送到中枢神经系统。只有当这些信号在大脑中被处理时，它们才会被感知为声音或运动。因此，内耳和中枢神经系统之间的神经元连接的发育对内耳的功能以及声音和运动的感知至关重要。神经元前体的产生是内耳发育的早期事件。在简单上皮层内，一群细胞开始发育成神经元。它们从上皮细胞迁移到周围组织，在那里它们结合形成耳蜗-前庭神经节。随后，它们产生生长回上皮的突起，连接到感觉毛细胞，并连接到中枢神经系统的听觉和前庭中枢。这些事件需要细胞间相互作用的动态变化，驱动它们从上皮细胞释放，支持它们的迁移，并指导过程的生长到正确的目标。细胞相互作用是由许多细胞表面分子控制的，当它们与邻近细胞表达的表面伴侣（配体）结合时，这些分子向细胞内发送信号。细胞信号传导导致细胞行为的改变，例如，引起细胞被配体的来源吸引或排斥。一个这样的细胞表面分子家族是Eph受体酪氨酸激酶（Ephs）及其配体ephrin。这些分子之间的相互作用在神经系统的组织中具有重要作用，但它们在内耳神经支配的早期发育中的作用尚未被研究。本研究的目的是为了更好地了解Eph/ephrin相互作用在内耳神经支配发育中的作用。我们将重点关注两个事件：第一，神经元前体从早期内耳上皮迁移，第二，神经元突的早期生长。为了解决这些问题，我们将进一步开发一种目前正在实验室中使用的耳上皮外植体系统，以允许操纵Ephs和ephrin的表达。改变这些分子的表达对神经母细胞迁移和过程形成的影响将在培养中使用延时显微镜和免疫组织化学进行监测。这些实验将进一步加深我们对内耳和其他来自上皮的器官（如嗅觉系统）的神经元发育的理解。在培养中操纵发育器官中重要分子表达的新技术的发展将有助于未来对这些器官发育的研究。此外，这些实验将有助于研究损伤后的神经再生，并通过阐明促进神经向植入电极生长的潜在策略，从而提高植入物的性能，从而潜在地影响人工耳蜗的发展。

The inner ear is a highly complex architectural and functional structure that is exquisitely organised to detect sound and movement, yet it develops from a simple sheet of epithelial cells. During development this epithelium must generate and organise all of the major cell types found in the mature organ, including the specialised sensory hair cells that detect the sound or movement, the non-sensory cells that support sensory cell function and the neurones that connect the organ to the central nervous system. The sensory cells detect the sound or movement stimuli and convert these into signals that are sent to the central nervous system via neurones. It is only when these signals are processed in the brain that they are perceived as sound or movement. Thus, the development of the neuronal connection between the inner ear and the central nervous system is crucial to the function of the inner ear and the perception of sound and movement. The generation of neuronal precursors is an early event during the development of the inner ear. Within the simple epithelial sheet a population of cells begin to develop as neurones. They migrate out of the epithelium into the surrounding tissue where they coalesce to form the cochlear-vestibular ganglion. Subsequently, they produce processes that grow back into the epithelium to connect to the sensory hair cells and towards the auditory and vestibular centres in the central nervous system. These events require dynamic changes in the cell-cell interactions that drive their release from the epithelium, support their migration and direct the growth of processes to the correct targets. Cellular interactions are controlled by numerous cell surface molecules that send signals into the cell when they bind to surface partners (ligands) expressed by neighbouring cells. The cell signalling results in changes in cell behaviour by, for example, causing the cell to be attracted to, or repelled from, the source of the ligand. One such family of cell surface molecules are the Eph receptor tyrosine kinases (Ephs) and their ligands the ephrins. Interactions between these molecules have previously been shown to have important roles in the organisation of the nervous system but their role in the early development of inner ear innervation has yet to be investigated. The aim of the work proposed here is to better understand the role of Eph/ephrin interactions in the development of inner ear innervation. We will focus on two events: first, the migration of neuronal precursors out of the early inner ear epithelium and second, the early growth of neuronal processes. To address these questions we will further develop an otic epithelial explant system that is currently being used in the lab in order to allow manipulation of the expression of Ephs and ephrins. The effect of changing the expression of these molecules on neuroblast migration and process formation will then be monitored in culture using timelapse microscopy and immunohistochemistry. These experiments will further our understanding of neuronal development of the inner ear and other organs derived from epithelia, such as the olfactory system. The development of a novel technique to manipulate expression of important molecules within a developing organ in culture will facilitate future studies into the development of these organs. In addition, these experiments will aid research into nerve regeneration following damage and potentially influence the development of cochlear implants by elucidating potential strategies to encourage neural growth towards implant electrodes, thereby, enhancing the implant performance.