FIG. 1.

TUNEL analysis of Prep1^i/i embryos. Sections of Killik-embedded E9.5 WT (+/+) and Prep1^i/i (i/i) embryos were stained by TUNEL to detect apoptosis, and nuclei were counterstained with Hoechst stain (see Materials and Methods). The white arrowheads indicate neural and intersomitic regions; the empty arrowheads indicate other nonneural tissues.