A gene trap vector containing a beta-geo cassette inserted into the 3 prime end of the gene between two introns that encode the armadillo repeat region. A fusion gene product resulted where the last 46 amino acids of the endogenous gene product was replaced with betageo. Northern blot analysis on homozygote E11.5 embryos indicate only the fusion gene product is expressed. LacZ expression was detected throughout the vasculature of embryonic and adult heterozygote mice.