Fig. 1. Development and cellular anatomy of the mouse organ of Corti. (A-E) Cochlear epithelia from E12.5-E17.5 from mice carrying a transgenic Math1-GFP reporter (Chen et al., 2002; Lumpkin et al., 2003). Epithelia were dissected and photographed under brightfield conditions and fluorescence images of Math1/GFP expression (green) from the same preparations were superimposed to illustrate the basal to apical pattern of hair cell differentiation that initiates in the mid-basal regions of the cochlea at E14.5 (Chen et al., 2002) and spreads apically until E17.5 when the wave of differentiation is complete. Note that at E12.5 and E13.5 Math1/GFP expression is limited to the saccule where Math1-dependent hair cell differentiation begins around E10.5 (Bermingham et al., 1999). (F) Cross-section through a P1 organ of Corti illustrating the position of hair cells (green, stained with antibody to Myosin VIIa) and supporting cells (red, stained with antibody to p27^Kip1). The different varieties of hair cells and supporting cells are labeled: I, inner hair cell; O1-O3, outer hair cell-row 1-3; IP, inner phalangeal.