Figure 1.

The death of hair cells (yellow) in the cochlea of chicks (left panels) stimulates the surrounding supporting cells (red) to re-enter the cell cycle and differentiate as new hair cells. In mammals, the death of cochlear hair cells is permanent. Supporting cells do not normally re-enter the cell cycle and no regeneration occurs. The red arrow indicates the stereocilia bundle of a single chick hair cell. The red asterisk and brackets indicate the position of the single row of inner hair cells and three rows of outer hair cells typically found in mice and humans. (Scanning electron micrographs are courtesy of Dr. Ed Rubel and House Ear Institute.)