Fig. 5. Cell-type-specific transcriptional regulation of p27^Kip1 in the postnatal organ of Corti and retina. (A-C) Sections through the postnatal day 1 (P1) organ of Corti triple-labeled with antibody to p27^Kip1 (A), the native p27^Kip1/GFP transgene (B) and the hair cell marker Myosin VIIa (C). Note high levels of p27^Kip1 expression in postnatal supporting cells and the lack of staining of differentiated hair cells, indicating that p27^Kip1 is downregulated in hair cells at the transcriptional level. (D-G) Cross-sections through the P21 mouse retina. D and E are the same section double-labeled with antibody to glutamine synthetase, a marker of Muller glia in the retina (D), and the native p27^Kip1/GFP transgene (E). F and G are the same section double-labeled with antibody to p27^Kip1 (F) and the native p27^Kip1/GFP transgene (G). Note the co-linearity of staining between glutamine synthetase, the p27Kip1 protein and p27^Kip1/GFP in the inner nuclear layer (INL), which is indicative of cell-type-specific transcriptional control in the postnatal retina. ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. Scale bar: 100 µm.