Hair cell differentiation becomes tissue specific by E9.5 in mouse inner ear.

Tissue culture is a standard method to study tissue interactions during embryogenesis. The serum that is usually used in culture can, however, confound results as it includes unidentified factors. In this study, we used a serum-free otocyst culture to investigate the tissue interactions that determine hair cell fate in mice otocysts. Otocysts cultured with surrounding tissues have the ability to produce mature hair cells in serum-free otocyst culture. Although isolated otocysts from E9.5 mice produced hair cells, those from E9.0 mice could not. This indicates that the mouse otocyst gains the ability to generate hair cells between E9.0 and E9.5 and that this ability depends on signals from the surrounding mesenchyme and/or the hindbrain.