A cDNA encoding amino acids 198-695 with a deletion of amino acids 341 to 348, an amino acid substitution of leucine for proline at position 542 (L542P) and a floxed neo cassette were knocked into exon d. The neo cassette was removed by cre-mediated recombination following a cross to a cre deleter strain (Tg(CMV-cre)1Cgn). The modification to the coding region is thought to interfere with protein-protein interactions with Grb2. Expression of the mutant protein confirmed by western blot analysis on protein extracts from E12 embryos was reduced by 40% to 50% relative to levels in wild-type mice.