Regulation of Elongation, Growth and Coiling of the Mammalian Cochlea

耳蜗管的生长、伸展和卷曲是耳蜗管发育的关键步骤。我们实验室和其他实验室以前的结果表明，一条进化上保守的被称为平面细胞极性(PCP)的途径在耳蜗的发育中发挥了作用。然而，PCP途径中的任何分子都不能产生耳蜗长出所需的分子作用力。最近，一种特殊的肌球蛋白分子，非肌肉肌球蛋白II，被认为是PCP途径的效应器。因此，我们试图确定肌球蛋白II是否在耳蜗发育中发挥作用。对肌球蛋白重链基因肌球蛋白IIA、肌球蛋白IIB和肌球蛋白IIC的定位表明，肌球蛋白IIB和IIC在发育中的耳蜗管中均有表达。此外，体外对肌球蛋白II的药理抑制抑制了耳蜗的生长，表明肌球蛋白II在这一事件中发挥了重要作用。为了确认肌球蛋白II的作用，我们只在发育中的内耳表达了一个显性的阴性版本的肌球蛋白IIB。使用显性负值是因为肌球蛋白IIB或IIC的单个缺失没有表型，这是这两个基因之间功能补偿的结果。由于导管内细胞生长的缺陷，显性阴性肌球蛋白IIB的表达导致耳蜗短。正在进行的实验将确定肌球蛋白II作用的分子作用以及该作用在耳蜗长出中的基础。

Outgrowth, extension and coiling are key steps in the development of the cochlear duct. Previous results from our laboratory and others have indicated that an evolutionarily conserved pathway referred to as the planar cell polarity (PCP) pathway plays a role in cochlear outgrowth. However, none of the molecules in the PCP pathway act to generate the molecular force necessary for cochlear outgrowth. Recently, a specific myosin molecule, non-muscle myosin II, has been implicated as an effector of the PCP pathway. Therefore, we sought to determine whether myosin II plays a role in cochlear outgrowth. Localization of the three different Myosin heavy chain genes, Myosin IIA, IIB and IIC, indicated that Myosin IIB and IIC are both expressed in the developing cochlear duct. Moreover, pharmacological inhibition of myosin II in vitro inhibited cochlear outgrowth, indicating that myosin II plays an important role in this event. To confirm the role of myosin II, we expressed a dominant negative version of Myosin IIB exclusively within the developing inner ear. A dominant negative was used because single deletions of either Myosin IIB or IIC had not phenotype as a result of functional compensation between the two genes. Expression of dominant negative Myosin IIB leads to shortened cochleae as a result of defects in the growth of cells within the duct. Ongoing experiments will determined the molecular role of myosin IIs action and the basis for that action in cochlear outgrowth.