Shaping the mammalian auditory sensory organ by the planar cell polarity pathway

Abstract

The human ear is capable of processing sound with a remarkable resolution over a wide range of intensity and frequency. This ability depends largely on the extraordinary feats of the hearing organ, the organ of Corti and its sensory hair cells. The organ of Corti consists of precisely patterned rows of sensory hair cells and supporting cells along the length of the snailshaped cochlear duct. On the apical surface of each hair cell, several rows of actin-containing protrusions, known as stereocilia, form a "V"-shaped staircase. The vertices of all the "V"-shaped stereocilia point away from the center of the cochlea. The uniform orientation of stereocilia in the organ of Corti manifests a distinctive form of polarity known as planar cell polarity (PCP). Functionally, the direction of stereociliary bundle deflection controls the mechanical channels located in the stereocilia for auditory transduction. In addition, hair cells are tonotopically organized along the length of the cochlea. Thus, the uniform orientation of stereociliary bundles along the length of the cochlea is critical for effective mechanotransduction and for frequency selection. Here we summarize the morphological and molecular events that bestow the structural characteristics of the mammalian hearing organ, the growth of the snail-shaped cochlear duct and the establishment of PCP in the organ of Corti. The PCP of the sensory organs in the vestibule of the inner ear will also be described briefly.

Role of chromatin remodeling gene Cecr2 in neurulation and inner ear development

“…4C). These observations agree with different waves of maturation occurring within the organ of Corti at this time (Kelly and Chen, 2007). The Cecr2 tm1.1Hemc homozygous mutants appeared less severe than the Cecr2 Gt45Bic line at the IHC, OHC1, and OHC2 layers (Fig.…”

Cell shape and epithelial patterning in the Drosophila embryonic epidermis

“…A classic example is the array of stereociliary bundles in the vertebrate inner ear that is vital for hearing. 1 Epithelial development is an intricate series of events encompassing cell division, cell death, cell rearrangements and morphogenetic movements. How can such a complex process cumulate in the formation of precise structural arrays?…”

“…8,9 Fz PCP signaling is not restricted to wing hair organization, but is also required to control Drosophila bristle orientation, 10 ommatidial polarity, 11 aristal branching, 12 tarsal joint formation 13 and tissue topography. 14 The Fz PCP pathway appears to be conserved in vertebrates and components of the pathway are known to be required for convergent extension movements during embryogenesis, 15 the organization of stereociliary bundles in the inner ear, 1 fur patterning, 16 cardiovascular development, 17 axonal guidance 18 and are permissive for Sonic Hedgehog signaling. 19 The Drosophila larval cuticle is also patterned with regular arrays of polarized structures.…”

The molecular biology of ear development - "Twenty years are nothing"

“…As mammalian PCP pathway regulates the establishment of the characteristic polarity of stereocilia and convergent extension, but they seem not to be mutually dependent. As discussed in the article by Chen (2007) there are various possible models that couple general cues to specific cell behaviors that seem to involve at least the link of Wnt signaling with the intrinsic PCP machinery that drive cell asymmetries. Chen postulates that multiple directional signals converge into the core PCP complexes that are sorted asymmetrically along the medio-lateral axis of the cochlea.…”

“…The cochlea contains a precise pattern along the logitudinal axis, with a graded variation of mechanical properties of the basilar membrane and of electrical properties of hair cells, that enable the precise tuning of hair cells in a tonotopic pattern. Ping Chen in this issue (Chen, 2007) discusses histogenesis and the interesting "convergent extension hypothesis" of cochlear morphogenesis. Convergent extension is a process of tissue narrowing along one axis with the concomitant extension along a perpendicular axis, the best known example being amphibian gastrulation (Keller, 2002).…”