UAS regulatory sequences drive expression of Dl, with a Tag:MYC tag inserted in the extracellular domain between EGF-like repeats 3 and 4. The tag has been inserted in a BglII site to give a protein with amino acids E331 and I332 repeated before and after the Tag:MYC tag, i.e. N-terminus to E331-I332-Tag:MYC tag-E331-E332-Y333 to C-terminus.