Function of LIM-domain Transcriptional Regulators in Inner Ear Development

描述（由申请人提供）：耳聋疾病的主要原因源于内耳毛细胞的变性，尽管在许多情况下，这些疾病的潜在机制尚不清楚。通过定义控制正常毛细胞发育的机制，我们将更好地了解这些过程在病理情况下如何被破坏以及毛细胞如何再生。该建议的中心假设是，LIM同源结构域转录因子Isl 1的表达提供了腹侧耳蜗上皮形成感觉器官的能力，并且LIM结构域仅转录调节因子LMO 3和LMO 4对Isl 1功能的负调节限制了推定OC（OC）区域的能力。在我们的初步研究中，我们已经表明，在耳蜗的感觉发育在E12.5至E16.5，Isl 1表达在一个广泛的域在腹侧耳蜗上皮，包括推定的OC。有趣的是，LMO 3的表达在小上皮嵴（LER）中检测到，而LMO 4的表达局限于大上皮嵴（格尔）和远端LER（dLER）。LMO 3和LMO 4的组合表达结构域与Isl 1的表达结构域重叠，除了在Isl 1单独表达的假定OC区域。与我们的假设一致，我们已经表明，LMO 4的损失导致在dLER中形成额外的毛细胞，证实了LMO 4作为感觉器官发育的负调节剂的作用。因此，基于LMO蛋白在抑制LIM-HD蛋白的转录调节功能中的既定作用，Isl 1、LMO 3和LMO 4的联合作用可以决定OC区域的形成。为了验证这一假设，并探讨LIM域因子在内耳发育中的作用，我们提出了以下三个具体目标：1）。通过靶向破坏LMO 4来确定耳蜗和前庭中感觉和神经元发育对LMO 4的需求; 2）。确定LMO 4在假定的前感觉区中的异位表达是否通过Isl 1表达细胞中LMO 4表达的条件性激活来抑制感觉发育;和3）。通过Isl 1的条件性缺失来确定Isl 1在内耳感觉和神经元发育中的作用。Corti器官中内耳毛细胞的损失是听力损失的主要原因，影响全球2.78亿人，其中包括美国的2800万人。然而，由于毛细胞的损失是一个不可逆的过程，哺乳动物内耳缺乏再生毛细胞的能力，有效的补救措施，以取代毛细胞仍然难以捉摸。本申请中提出的研究将为内耳感觉器官形成的分子机制提供新的见解，并可能导致通过从头毛细胞再生治疗和最终治愈耳聋的新方法。这个建议的中心假设是，LIM同源结构域转录因子的表达提供了腹侧耳蜗上皮细胞的能力，形成的感觉器官和LIM域的转录调节抑制LIM同源结构域因子的作用，在腹侧耳蜗除了推定的器官Corti区域。因此，LIM-homeodomain和LIM-domain-only因子的组合功能调节腹侧耳蜗上皮的能力，并决定了推定的Corti器官的区域。

DESCRIPTION (provided by applicant): A major cause of deafness disorders stem from the degeneration of hair cells within the inner ear although in many cases the mechanisms underlying these disorders is not understood. By defining the mechanisms controlling normal hair cell development, we will gain a better understanding of how these processes are disrupted in pathological situations and how the hair cells can be regenerated. The central hypothesis of this proposal is that the expression of the LIM-homeodomain transcription factor Isl1 provides the ventral cochlear epithelium with a competence to form the sensory organ and that the negative regulation of Isl1 function by the LIM-domain-only transcriptional regulators LMO3 and LMO4 restricts the competence to the presumptive OC (OC) region. In our preliminary studies, we have shown that during the sensory development in the cochlea at E12.5 to E16.5, Isl1 is expressed in a broad domain in the ventral cochlear epithelium, including the presumptive OC. Interestingly, the expression of LMO3 is detected in the lesser epithelial ridge (LER), whereas LMO4 expression is confined to the greater epithelial ridge (GER) and to the distal LER (dLER). The combined LMO3 and LMO4 expression domain overlaps with that of Isl1 except in the presumptive OC region where Isl1 is expressed alone. Consistent with our hypothesis, we have shown that loss of LMO4 results in the formation of supernumerary hair cells in the dLER, confirming a role for LMO4 as a negative regulator of sensory organ development. Thus, based on the established roles of LMO proteins in inhibiting LIM-HD proteins' function in transcriptional regulation, the combined action of Isl1, LMO3 and LMO4 could determine the formation of the OC region. In order to test this hypothesis and investigate the roles of LIM-domain factors in the inner ear development, we propose the following three specific aims: 1). To determine the requirement for LMO4 in the sensory and neuronal development in the cochlea and vestibule by targeted disruption of LMO4; 2). To determine whether the ectopic expression of LMO4 in the presumptive prosensory region represses the sensory development by the conditional activation of LMO4 expression in the Isl1-expressing cells; and 3). To determine the role of Isl1 in the sensory and neuronal development of the inner ear by the conditional deletion of Isl1. PUBLIC HEALTH RELEVANCE Loss of the inner ear hair cells in the organ of Corti is the leading cause of hearing loss that affects 278 million people worldwide, including 28 million in the United States. However, since the loss of hair cells is an irreversible process and mammalian inner ear lacks the capability to regenerate hair cells, effective remedies to replace hair cells remain elusive. The studies proposed in this application will provide new insights into the molecular mechanisms underlying the sensory organ formation in the inner ear and could lead to novel approaches in the treatment and eventual cure of deafness by de novo hair cell regeneration. The central hypothesis of this proposal is that the expression of the LIM-homeodomain transcription factor provides the ventral cochlear epithelium with the competence to form the sensory organ and that the LIM-domain-only transcriptional regulators suppress the role of LIM-homeodomain factor in the ventral cochlea except the presumptive organ of Corti region. Thus, the combined function of LIM-homeodomain and LIM-domain-only factors regulates the competence in the ventral cochlear epithelium and determines the region of the presumptive organ of Corti.