The L1L2_Pgk_P cassette was inserted at position 20679037 of Chromosome 14 upstream of exon 3. The cassette is composed of an FRT site followed by lacZ sequence and a loxP site. This first loxP site is followed by neomycin resistance gene under the control of the PGK promoter, SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of exon 3 at position 20679926. A null allele was created by flp and cre recombinase expression in mice, resulting in the deletion of the lacZ sequences, the neomycin selection cassette and exon 3.