An ADAM family member with expression in thymic epithelial cells and related tissues

We have analyzed the tissue-specific expression, mRNA isoforms, and genomic structure of murine ADAM28, an ADAM family member recently discovered in human and mouse. While human ADAM28 is expressed in lymphocytes (J. Biol. Chem. 274 (1999) 29251), we observe expression of murine ADAM28 in thymic epithelial cells and developmentally related tissues including the trachea, thyroid, stomach, and lung, but not in lymphocytes. The expression patterns in adult and day 15.5 embryos are similar. We have detected multiple mRNA isoforms varying in the cytoplasmic domain coding sequence and 3prime prime or minute untranslated region due to alternative polyadenylation and splicing events that occur in the final four exons and three introns. The entire ADAM28 gene spans 55 kb and contains 23 exons. The protein sequence contains all conserved residues required for metalloprotease activity, indicative of a role in ectodomain shedding and extracellular matrix modeling. Given its unique expression pattern and potential functions, murine ADAM28 may play a role in organogenesis and organ-specific functions such as thymic T cell development.