A reaction-diffusion model of hair-bundle morphogenesis

With the notable exception of those in the mammalian cochlea, the hair bundles of many species and receptor organs display a similar structure. Stereocilia arranged in a hexagonal pattern cover a portion of the apical surface of a hair cell, with stereociliary lengths that grow progressively in the direction of the kinocilium to form the characteristic staircase shape. To organize stereocilia in this particular arrangement, a developing hair cell must convey the information necessary to define the boundary of the hair bundle, determine the hexagonal arrangement of the stereocilia, and produce a height gradient.
In this work we propose a reaction-diffusion model to explain how a hair cell might solve this problem. Using this model we predict that a hair cell needs at least two sources of morphogens, the cell boundary and the kinocilium, to produce the observed hair bundle. We are also able to predict how bundles will change under certain perturbations that might now be tested experimentally.