Pitx2cre; N-lacZ lineage tracing approach labels Pitx2 mutant neurons. (A) Pitx2cre/+ embryos were mated with Pitx2+/null; N-lacZ/N-lacZ mice to yield embryos of four possible genotypes. Pitx2cre/+;N-lacZ (B) and Pitx2cre/null:N-lacZ (C) embryos express β-galactosidase in Pitx2-expressing tissues at E12.5, including the eye, hypothalamus (hyt), midbrain (mb), heart (h), craniofacial structures, and somites. Pitx2cre/null;N-lacZ embryos exhibit lethality after E14.5, likely due to cardiac and abdominal defects that are not well visualized in this sagittally oriented embryo (C).