Genomic architecture of Shh dependent cochlear morphogenesis

小鼠耳蜗起源于耳小泡的腹侧延伸。在过去的几年中 在胚胎发育的几天里，这个副产物经历了一系列复杂的形态发生 导致其延长、卷曲和分化为感觉和非感觉细胞类型的变化 这对于听力来说是必不可少的(Groves和Fekete，2012)。先天性耳蜗术后畸形常导致 失聪，强调了彻底了解其发展的重要性(Jackler等，1987)。 我们先前描述了Sonic hedgehog(Shh)信号通路在促进 耳囊内的腹侧身份，对于随后的耳蜗管突起是必要的 (Riccomagno等人，2002年；Bok等人，2007b；Brown和Epstein，2011年)。缺乏Shh的小鼠胚胎，或 对Smoothens(Smoecko)进行耳部条件性敲除，这是一种重要的Shh信号转导途径 部件，表现为耳蜗性发育不良。我们还对几种转录因子进行了分类，这些转录因子在 Shh转录靶点(Pax2、OTX2、GATA3)或效应物(Gli2、Gli3)的耳蜗发育 腹侧耳廓上皮内的信号。然而，尽管取得了这些进展，但对 Shh依赖的转录因子促进耳蜗管生长的机制尚不清楚。 主要是因为在转录级联中下游起作用的基因还没有确定。 为了确定Shh信号的新靶点，我们比较了对照的全基因组表达谱 在E11.5的Smoecko内耳，当耳蜗骨突出时，发现了一组耐人寻味的Shh 具有已知和先前未知角色组合的耳蜗反应基因 形态发生。有趣的是，这些基因中有几个在发育后期保持其表达。 在耳蜗管的前感觉域内，Shh信号可能正在启动 在其发育的后续步骤中推定的感觉上皮。我们建议将其描述为 腹侧耳道基因集根据以下实验计划：分类它们的时空模式 对Shh信号的表达和依赖(目标1)；解码它们的顺式调控结构(目标2)；以及 评估它们对耳蜗发育的功能贡献(目标3)。这些实验的结果应该是 促进我们对耳蜗分子和细胞机制的基本理解 内耳的形态发生和细胞命运的规定。

The mouse cochlea derives from the ventral extension of the otic vesicle. Over the course of several days during embryonic development, this outgrowth undergoes a complex sequence of morphogenetic changes resulting in its lengthening, coiling and differential patterning into sensory and nonsensory cell types that are essential for hearing (Groves and Fekete, 2012). Congenital malformations of the cochlea often lead to deafness, emphasizing the importance of a thorough understanding of its development (Jackler et al., 1987). We previously described a critical function of the Sonic hedgehog (Shh) signaling pathway in promoting ventral identity within the otic vesicle that is necessary for the subsequent outgrowth of the cochlear duct (Riccomagno et al., 2002; Bok et al., 2007b; Brown and Epstein, 2011). Mouse embryos lacking Shh, or carrying an ear conditional knockout of Smoothened (Smoecko), an essential Shh signal transduction component, exhibit cochlear agenesis. We also classified several transcription factors with key roles in cochlear development as either transcriptional targets (Pax2, Otx2, Gata3) or effectors (Gli2, Gli3) of Shh signaling within the ventral otic epithelium. However, despite these advances, a detailed understanding of the mechanism by which Shh dependent transcription factors promote cochlear duct outgrowth remains unclear, primarily since the genes acting downstream in this transcriptional cascade have yet to be determined. To identify novel targets of Shh signaling we compared the genome-wide expression profiles of control and Smoecko inner ears at E11.5, when the cochlea anlage is evident, and uncovered an intriguing set of Shh responsive genes with a combination of known and previously uncharacterized roles in cochlear morphogenesis. Interestingly, several of these genes maintain their expression at later stages of development within the prosensory domain of the cochlear duct, raising the possibility that Shh signaling is priming the presumptive sensory epithelium for subsequent steps in its development. We propose to characterize the ventral otic gene set according to the following experimental plan: classify their spatiotemporal patterns of expression and dependency on Shh signaling (Aim 1); decode their cis-regulatory architecture (Aim 2); and assess their functional contribution to cochlear development (Aim 3). The results of these experiments should advance our fundamental understanding of the molecular and cellular mechanisms underlying cochlear morphogenesis and cell fate specification within the inner ear.