A knock-in allele, in which Tag:OLLAS is inserted in the active domain of the otherwise wild-type dpp protein, in the ligand domain immediately after the most C-terminal proconvertase cleavage site. The mutagenesis method took advantage of two transposable elements (Mi{MIC}dppMI03752 and PBac{RB}e00178) flanking the second (last) coding exon of dpp.