Molecular cloning of bovine CD97: an EGF-TM7 molecule expressed as isoforms

CD97, a cell surface molecule on immune cells with potential adhesive function, is a member of the epidermal growth factor seven-span transmembrane (EGF-TM7) family. We have cloned and characterized bovine CD97 and determined its expression in various cells and tissues. Based on sequence alignment with human genomic DNA, as well as human cDNA sequences encoding various CD97 isoforms, we predict that bovine CD97 mRNA occurs in four splice variants. The encoded CD97 isoforms (800, 751, 756, and 707 amino acids in length) contain different numbers of EGF-like modules, a stalk region, and a TM7 domain with a cytoplasmic tail. RT-PCR demonstrated expression of CD97 mRNA in leukocytes and several other tissues. In each cell type, CD97 mRNA encoding the shortest isoform, CD97 (EGF 1,2,5), was detected at the highest level, which was consistent with the cell surface expression of a 90-kDa polypeptide precipitated from lysates of peripheral blood mononuclear cells.