A T583M mutation (ACA to ATG) was created in exon 16 using site-directed mutagenesis and then knocked into the open reading frame. A floxed neo cassette used for ES cell selection was removed by cre-mediated recombination via a cross to a deleter Cre line (not specified). Insertion of the point mutations was confirmed by sequencing exon 16 in ES cells. Comparable protein expression to wild-type was confirmed by western blot and RT-PCR of 3 week old growth plate cartilage.