Fig. 1. Targeting strategy and expression pattern of Hand1. (A) A region of the first exon of the Hand1 gene was replaced with the lacZ gene to monitor Hand1 expression. The coding region is shown as black shading and the 5' and 3' untranslated regions shown as gray shading. The targeting vector is shown in the middle. The lacZ gene was inserted in frame with the initiating methionine of the Hand1 gene and PGKneo gene was inserted in the opposite orientation to the transcription of Hand1. The MC1TK cassette was linked to the 3' untranslated region of Hand1 to provide negative selection with FIAU. (B-E) Hand1 expression is recapitulated by ß-gal expression during Hand1^ß-gal/+ mouse development at 7.75 dpc (B), 10.5 dpc (C), 12.5 dpc (D) and 14.5 dpc (E). Embryos in D and E were cleared using benzyl alcohol and benzyl benzoate (1:2 ratio). ad, adrenal gland; h, heart; ht, heart tube; g, gut; lm, lateral mesoderm; m, mandible and tongue; scg, superior cervical ganglia; st, sympathetic trunk; t, thyroid; u, umbilical cord and gut.