The gene trap vector was inserted 5016 bp downstream of exon 1. RT-PCR confirmed the expression of an fusion transcript between exon 1 and the gene trap vector. Real time PCR detected expression of wild type transcript in hearts from homozygous mice at about 3% of the level seen in wild-type hearts. LacZ expression was detected in the developing heart, axial skeleton, neocortex, spinal cord, and eye. Postnatally expression was seen in the heart, retina, ovary and testis. (J:147372)