FIXING AND STAINING CELLS – A QUICK METHOD. Require: 1) 3.7% formaldehyde in PBS or 4% parafomaldehyde or methanol:acetone (1:1) 2) 0.1% Triton X-100 in PBS 3) 10% FCS, 0.5% BSA in PBS Method: 1) Aspirate medium from cells and fix in 3.7% formaldehyde or 4% paraformaldehyde or methanol:acetone IN THE FUME HOOD for 15 min. 2) Remove fixing solution and pour down fume hood sink. Wash and permeabilise the cells 3 X 5 min. with 2ml of 0.1% Triton X-100 in PBS. (NB I think you can miss this step if you have fixed your cells in methanol:acetone as they will have been permeabilised at the fixing stage however when staining centrosomes I have found that the results are cleaner if this step is included). 3) Transfer coverslips to 24 well plate lid in a humid black box. DO NOT ALLOW TO DRY OUT. 4) Block with 100ul of 10% FCS, 0.5% BSA in PBS for 30 min. 5) Remove blocking solution and replace with the primary antibody/antibodies at 1/100 dilution in 10% FCS, 0.5% BSA in PBS. Incubate for 1 hour (at least) at room temperature. 6) Wash 3 X 5 min. with 100ul 10%FCS, 0.5% BSA in PBS. 7) Incubate with 100ul of the secondary antibody/antibodies at 1/100 dilution in 10% FCS, 0.5% BSA in PBS for 40 min. At this point add propidium iodide 1/100 dilution of 1mg/ml stock. KEEP IN THE DARK AS MUCH AS POSSIBLE FROM THIS STAGE ONWARDS. 8) Wash 2 X 5 min. with 10% FCS, 0.5% BSA in PBS followed by 1 X 5 min. wash in 0.1% Triton X-100. 9) Mount on glass slide with vectashield or something similar.