Fig. 7. Cultured Cdx2^-/- embryos exhibit excessive cell death at the expanded blastocyst stage. (A-B') Composite images of single confocal optical sections superimposed on DIC images. Zona pellucida-free eight-cell stage embryos from Cdx2^+/– intercrosses were cultured for 48 hours followed by TUNEL analysis. (A) Cdx2^+/–; TUNEL-positive nuclei were detected in the ICM. (B,B') Cdx2^-/- blastocyst; TUNEL-positive nuclei were observed in the ICM and TE. (B') Optical section taken at a different level of the embryo in B. Scale bars: 25 µm. (C) The number of TUNEL-positive nuclei in the ICM and TE of Cdx2^+/+ or Cdx2^+/– embryos (n=16) and Cdx2^-/- embryos (n=7) was scored from confocal optical sections of individual embryos following TUNEL staining. The values plotted represent the mean number of TUNEL-positive nuclei (±s.e.m.). The increase in the number of TUNEL positive nuclei in the ICM and TE in Cdx2^-/- embryos compared with Cdx2^+/– or Cdx2^+/+ embryos was significant at P<0.001 using Student's t-test analysis.