Fig. 1.

Inactivation of NHEJ or HR affects different embryonic stages during mouse development. Widespread apoptosis can be found in the Xrcc2^−/− embryo by E10.5 and is illustrated showing neuroepithelium and adjacent cephalic mesenchyme. (A) Ki67 immunoreactivity (red) marks proliferating cells, and TUNEL staining (green) identifies cells undergoing apoptosis. (B) Although apoptosis is widespread in the proliferative cells of the Xrcc2^−/− embryo at E11.5, it is not detectable in WT or Lig4^−/− embryos until E12.5. In the differentiating hindbrain region at E14.5, Lig4, but not Xrcc2, loss is associated with apoptosis. (Magnification: ×200.)