A targeting construct was designed to introduce an IRES-iCre-GSG-2A-mTFP1 cassette in the 3 untranslated region of the Xcr1gene, 29base pair (bp) downstream of the stop codon. mTFP1 is the sequence coding for a monomeric, bright, and photostable version of Clavularia cyan fluorescent protein. After germline transmission, excision of the frt-neor-frt cassette was achieved through crossing with mice expressing an FLP recombinase (J:327136)