Nucleostemin as a possible progenitor marker of corneal epithelial cells

Purpose: Nucleostemin, a nuclear protein involved in the regulation of cell cycle and proliferation, is a candidate marker for various stem cells. We examined the expression of nucleostemin as a marker of differentiation and senescence in corneal epithelial progenitor cells. Methods: Nucleostemin expression in normal mouse corneal epithelium was examined by RT-PCR, as well as in cultured mouse corneal epithelial cells by immunohistochemistry. Co-expression with the progenitor markers p63 and Bmi-1, cytokeratin 14 and 19, the proliferating marker Ki67, differentiation markers cytokeratin 12 and involucrin, and with the senescent marker SA-β-gal were examined by immunohistochemistry. Correlation of cellular size and nucleostemin expression was also examined. Results: Nucleostemin expression was detected in mouse corneal epithelium by RT-PCR. Immunohistochemistry revealed that nucleostemin was expressed predominantly in basal and suprabasal cells of the whole cornea. The expression of nucleostemin was not associated with the expression of Ki67, K14, and K19, but with the expression of Bmi-1 and particularly with p63. Nucleostemin was not co-expressed with SA-β-gal in same cell. Conclusions: Nucleostemin can be used as a progenitor marker analogous to p63.