The targeting vector was designed with, from 5' to 3', a floxed-STOP cassette that contains a neomycin cassette, a constitutively active mutant form of the mouse ret proto-oncogene cDNA, a viral T2A sequence, and a human histone H2B fused to a constitutively active red enhanced green fluorescence protein (tdTomato). The mutation in Ret is found in patients with multiple endocrine neoplasia type 2A. (J:305439)