Part of the hh first exon (including the ATG site and all the coding sequence of this exon) has been deleted. The following sequence has been inserted in place of the deleted hh sequence: a single attP site and a loxP cassette which itself contains an mFRT71 cassette followed by Scer\GAL4 coding sequence and a polyadenylation signal (this GAL4 sequence is non-functional). The mFRT71 cassette contains 1: the mCherry coding region tagged with a membrane-targeting signal (Tag:Myr(Unk)) and followed by a polyadenylation signal, 2: a w+* marker. The mCherry coding region is expressed under the control of the endogenous hh regulatory sequences.