Fig. 4. Caspases are activated earlier in young TA (yTA) than in KSC. Keratinocytes were separated on type IV collagen as described in Materials and Methods and suspended in polypropylene. Cells were then lysed at different time points and analyzed by western blot. Membranes were blotted against anti-Bid, and anti-procaspase-3, -6, -8 and -9 antibodies. ß-actin was used to normalize protein content.