EGFP (enhanced green fluorescent protein) cDNA was knocked into the second exon of the gene immediately after the endogenous start codon. A loxP-flanked neomycin resistance cassette was also inserted right after the EGFP sequence. The targeting vector was introduced to an embryonic stem cell line derived from albino C57BL/6 mice. A cross with a C57BL/6 background EIIa-Cre mouse excised the neomycin cassette. (J:156990)