This hypomorphic allele was generated by nucleotide substitution in exon 2 that results in the amino acid substitution of alanine for serine at positions 2, 4, 7, 12 and 13(S2A/S4A/S7A/S12A/S13A). Cre-mediated recombination removed the floxed neo cassette inserted upstream of the translation start site in exon 2. (J:180517)