FIG. 3.

Fen1^−/− embryonic cells are hypersensitive to gamma radiation. E3.5 blastocysts were collected as described in Materials and Methods; and placed in M2. The genotypes indicated were determined by PCR. Blastocysts were untreated or gamma irradiated at 2 Gy (Gammacell 3000 Elan; 5.35 Gy/min) prior to incubation for 24 h and double staining with TUNEL reagents (red) and DAPI (blue). Representative photographs of blastocysts following either no radiation (Fen1^wt [A] and Fen1^−/− [B]) or gamma radiation (2 Gy) (Fen1^wt [C] and Fen1^−/− [D]). Extensive cell death in Fen1^wt E3.5 blastocysts is shown by TUNEL staining (red).