Fig. 4. (A,B) Expression of hTERT in pre-senescent cells abrogates telomere metaphase singlets. Pre-senescent BJ cells were infected serially with the pBABE-hTERT-eGFP retroviral vector and with a control empty vector. Metaphase cells at pre- and postinfection were subjected to combined FISH-IF using an antibody to GFP and probes for telomeric and control regions. Only GFP-positive cells were scored. (A) Two singlets at telomere 17p are evident in a GFP-positive pre-senescent cell after infection with a control vector. (B) A GFP-positive cell, 4 days after infection with an hTERT-containing vector, displaying two doublet FISH signals at telomere 17. The FISH signal is detected with Cy-3 (red) and the GFP with FITC (green), and the nucleus is stained with DAPI (blue). Bar, 10 µm.