Figure 1.

Developmental expression of p27^Kip1 in the mouse organ of Corti revealed by immunocytochemistry in radial sections. The organ of Corti is composed of two sensory cell types arranged in one row of IHCs and three rows of OHCs. There are five different types of supporting cells whose nuclei lie below or adjacent to the hair-cell nuclei. These types include inner phalangeal cells (IPC), inner and outer pillar cells (PC), Deiters’ cells (DC), and Hensen’s cells (HC). Hair-cell and supporting-cell regions are indicated by arrows. Labeling with antibodies against p27^Kip1 shows that the protein is expressed only in the supporting-cell nuclei and not in the hair-cell nuclei. (A) Wild-type (p27+/+) mouse at postnatal day 0. (B) p27+/+ mouse at postnatal day 7; note the partially opened tunnel of Corti to the right of the outer PC. (C) p27+/+ adult mouse; note the fully opened tunnel of Corti. (D) The organ of Corti of the adult p27−/− animal shows no labeling; note the partially occluded tunnel of Corti. (Bar = 50 μm.)