Mallo M
Department of Developmental Biology, Max-Planck Institute of Immunobiology, Stübeweg 51, Freiburg, D-79108, Germany.
Dev Biol. 2001 Mar 15;231(2):410-9. doi: 10.1006/dbio.2001.0154.
The middle ear allows animals to hear while moving in an aerial medium. It is composed of a cavity harbouring a chain of three ossicles that transmit vibrations produced by airborne sound in the tympanic membrane into the inner ear, where they are converted into neural impulses. The middle ear develops in the branchial arches, and this requires sequential interactions between the epithelia and the underlying mesenchyme. Gene-inactivation experiments have identified genes required for the formation of different middle ear components. Some encode for signalling molecules, including Endothelin1 and Fgf8, probable mediators of epithelial-mesenchymal interactions. Other genes, including Eya1, Prx1, Hoxa1, Hoxa2, Dlx1, Dlx2, Dlx5, and Gsc, are most likely involved in patterning and morphogenetic processes in the neural crest-derived mesenchyme. Mechanisms controlling formation of a functional tympanic membrane are also discussed. Basically, the tympanic ring, which serves as support for the tympanic membrane, directs invagination of the first pharyngeal cleft ectoderm to form the external acoustic meatus (EAM), which provides the outer layer of the membrane. Gsc and Prx1 are essential for tympanic ring development. While invaginating, the EAM controls skeletogenesis in the underlying mesenchyme to form the manubrium of the malleus, the link between the membrane and the middle ear ossicles.
中耳使动物在空气中移动时能够听到声音。它由一个腔室组成，腔内有一串三块听小骨，这些听小骨将鼓膜中空气传播声音产生的振动传递到内耳，在内耳中振动被转化为神经冲动。中耳在鳃弓中发育，这需要上皮细胞和其下方的间充质之间进行一系列相互作用。基因失活实验已经确定了形成中耳不同组成部分所需的基因。一些基因编码信号分子，包括内皮素1和Fgf8，它们可能是上皮-间充质相互作用的介质。其他基因，包括Eya1、Prx1、Hoxa1、Hoxa2、Dlx1、Dlx2、Dlx5和Gsc，很可能参与神经嵴衍生间充质中的模式形成和形态发生过程。文中还讨论了控制功能性鼓膜形成的机制。基本上，作为鼓膜支撑的鼓环引导第一咽裂外胚层内陷形成外耳道（EAM），外耳道提供了鼓膜的外层。Gsc和Prx1对鼓环发育至关重要。在向内凹陷的过程中，外耳道控制其下方间充质中的骨骼形成，以形成锤骨柄，即鼓膜与中耳听小骨之间的连接。
