Characterization and localization of side population cells in the lens

PURPOSE Side population (SP) cells were isolated and the possibility whether lens epithelial cells contain stem cells was investigated. METHODS Mouse lens epithelial cells were stained by Hoechst 33342 and then sorted by fluorescence-activated cell sorting (FACS). The expression of stem cell markers in sorted SP cells and the main population of epithelial cells were analyzed by quantitative real-time PCR. Localization of SP cells in the mouse lens was studied by fluorescence microscopy. RESULTS The sorted cells contained SP cells, which were no longer separable by FACS following treatment with verapamil. The number of SP cells decreased with aging, but the adult mouse lens still contained SP cells. Phase contrast microscopy revealed that SP cells were smaller in size than non-SP cells. SP cells were localized near the equator region in lens epithelial cell layers. SP cells expressed higher levels of the stem cell markers ATP-binding cassette transporter G2 (ABCG2), p75 neurotrophin receptor (p75NTR), nestin (nes), B-cell lymphoma 2 (Bcl2), and cell surface antigen Sca-1 mRNA than the main population cells. These results suggest that SP cells contain a high proportion of stem cells. CONCLUSIONS The SP cells in the lens contain stem cells, and these stem cells are localized around the germinative zone.