Fig. 4. Expression patterns in adult OE suggest that p18Ink4c rather than p27Kip1 maintains basal cells in a quiescent state. A, immunohistochemical labeling of PCNA (a marker of cell proliferation), p27Kip1, and p18Ink4c on adjacent sections in the olfactory mucosa from newborn mice (1 week old). Arrowhead, the basal lamina (bl) lining the OE. Some labeled cells are indicated by an arrow; nc, nasal cavity; ch, chorion; bc, basal cells; on, olfactory neurons; sc, supporting cells; scale bar, 100 µm. p27Kip1 and p18Ink4a (arrows) are restricted in areas close to the basal lamina as PCNA. B, the same material as in A but at a higher magnification. Scale bar, 40 µm. Expression of both p27Kip1 and p18Ink4c are seen in the basal cell layer. C and D, immunohistochemical labeling of PCNA, p27Kip1, and p18Ink4c on sections from adult mice without any treatment (C) or 4 days after destruction of the olfactory neurons by ZnSO4 intranasal injections (D); scale bar, 40 µm.