A neomycin resistance cassette replaced a 2.3kb segment of the gene, including part of the promoter and all of exons 1 and 2, which encode the cytoplasmic and transmembrane domains of the protein. Flow cytometric analysis of thymocytes from homozygous mutantt mice stained with anti-Dpp4 mAb showed no protein expression. ELISA measurements showed undetectable protein concentrations in the plasma of homozygous mutant mice. (J:62709)