Given the requirement for p63 Selleckchem BKM120 in
the genesis of HBCs during embryogenesis, p63′s expression in HBCs and its demonstrated role in regulating self-renewal in other epithelial stem cells, we hypothesized that it may play a critical role in regulating HBC cell fate in the postnatal olfactory epithelium. Indeed, we found that conditional inactivation of the p63 gene in HBCs results in defects in HBC self-renewal. Analysis of the conditional p63 knockout further revealed that p63 is required to suppress differentiation of HBCs into other cell types in the olfactory epithelium. Together, these results suggest that p63 promotes olfactory stem cell self-renewal, at least in part by inhibiting HBC differentiation. Our studies provide important insight into the genetic network regulating stem cell dynamics in the olfactory epithelium and reveal an intriguing parallel between stem cell regulation in this neuroepithelium and other epithelial tissues. As an approach toward identifying the genes expressed in the adult tissue stem cells of the olfactory epithelium, we dissociated cells from selleck chemicals the olfactory epithelium of 21- to 25-day-old postnatal (P21–25) mice and labeled them with a fluorescently tagged antibody to ICAM1, a cell-surface protein that is expressed exclusively by HBCs in the postnatal olfactory epithelium (Carter et al., 2004). ICAM1-positive and ICAM1-negative cells were purified by FACS
(Figure 1B). We then performed microarray-based transcriptome profiling (using the Affymetrix mouse 430.2 platform) on FACS-purified cells; pairs of ICAM1(+) and ICAM1(−) cell samples from three independent FACS runs were analyzed. Based on microarray analysis as well as quantitative RT-PCR, we found that transcripts known to be preferentially expressed by HBCs (Krt5, Krt14, Icam1, and Itgb4) were reproducibly enriched in the ICAM1(+)
population, whereas transcripts expressed by more mature cell types (Ascl1, Neurog1, Gap43, Omp, and Ost) Bay 11-7085 were depleted (see Figure S1 available online), indicating the effectiveness of the ICAM1-based FACS purification of HBCs. To identify genes showing reliable differences in expression between the two cell populations, for each probe set on the microarray we plotted the average log2 ratio of expression level in ICAM1(+) versus ICAM1(−) cells (M value = log2[ICAM1(+)/ICAM1(−)] versus −log10[p value]; Figure 1C); transcripts showing the most robust and consistent differences in expression display high M values with low p values and therefore reside toward the outer tips of the resulting “volcano” plot. One of the most highly enriched transcripts encodes the transcription factor p63 (Trp63; Figures 1C and S1). Given its established role in stem cell proliferation and self-renewal in other stratified epithelia, we focused on p63 as a potential regulator of the stem cell in the olfactory neuroepithelium.