UASt sequences regulate expression of Delta in which the extracellular domain has been replaced in its entirety by Tag:LIG(FSHb) and the intracellular domain has been mutated so that all 12 Lys residues downstream of the stop transfer peptide have been changed to Arg residues. The coding sequence is tagged with HRP immediately upstream of the Delta transmembrane domain. A single FRT site is present in between the UASt and coding sequences.