The initiation codon of heart and neural crest derivatives expressed transcript 1 (Hand1) gene was replaced with a β-galactosidase (lacZ) sequence followed by a neomycin resistance cassette in this strain, abolishing gene expression. HAND1 is a basic helix-loop-helix transcription factor expressed in the trophoblast giant cells, yolk sac, cardiac neural crest, lateral mesoderm, septum transversum, early limb buds, and within the myocardial cuff and left ventrical of the developing heart. Heterozygous mice are viable and fertile, while homozygotes die between E8.5 and E9.5 due to defects in heart, extraembryonic mesoderm, and yolk sac development. Lacz staining is detected in extraembryonic mesoderm adjacent to the cardiac crescent, lateral mesoderm, trophectoderm of the ectoplacental cone and extraembryonic mesodermal components of the chorion, amnion, allantois, and visceral yolk sac. Lacz staining is observed in the cardiac outflow tract and the left ventricle of the heart, appearing in cardiac tissue at E8.5.
