Sequence encoding the wls 5'UTR, coding region and 3'UTR, with the coding region tagged between amino acid residues 506 and 507 with GFP (resulting in GFP being expressed on the luminal side), has been inserted into the attP site present in TI{TI}wlsKO.attP. This allows expression of the GFP-tagged wls sequence under the control of endogenous wls regulatory sequences.